HK1126894B - Low optical loss electrode structures for leds - Google Patents

Description

Low light loss electrode structure of light emitting diode

Technical Field

The present invention relates to Light Emitting Diodes (LEDs). More particularly, the present invention relates to an electrode structure capable of reducing light loss and improving the brightness and/or efficiency of a light emitting diode.

Background

It is well known to use Light Emitting Diodes (LEDs) as indicators. For this purpose, LEDs have been widely used in consumer electronics. For example, red LEDs are often used to indicate power to certain devices, such as radios, televisions, recorders, etc.

Although current LEDs have generally proven to meet their intended goals, some of the drawbacks inherent in LEDs have reduced their overall efficiency and availability. For example, the light output of these current LEDs is sometimes not as large as expected. These inherent disadvantages limit the functionality of LEDs in certain applications, such as providing general lighting, e.g., ambient lighting. Even the highest power LEDs currently do not provide sufficient illumination for these applications.

At least some of the problems associated with insufficient brightness are due to the poor efficiency of current LEDs. The efficiency of LEDs is a comparison of the amount of light emitted and the amount of power consumed. The reason for the poor efficiency of LEDs is currently because the light generated is lost by internal absorption. This internal absorption limits the amount of light that can be extracted from an LED and reduces its luminous efficiency.

Thus, while current LEDs have generally proven to meet their intended goals, some of the drawbacks inherent in LEDs have reduced their overall efficiency and availability. Accordingly, it is desirable to provide LEDs with increased brightness and/or efficiency.

Disclosure of Invention

The systems and methods disclosed herein provide brighter and/or more efficient light emitting diodes. For example, according to one embodiment of the present invention, a light emitting diode includes a reflective electrode structure including a metal electrode.

In particular, the electrode may be formed on a semiconductor material that emits light having a central wavelength λ. The light is emitted in various directions. A relatively thick, transparent dielectric material may be formed over the semiconductor material. A portion of the electrode may be formed on the relatively thick dielectric material. Another portion of the electrode is in electrical contact with the semiconductor material. The electrode and the thick dielectric material cooperate to enhance reflection so that light directed toward the electrode is reflected back into the semiconductor material, thereby providing additional opportunity to extract light from the light emitting diode.

The term "wavelength (λ)" as used herein refers to the wavelength of light propagating within the material. Thus, if light propagates within a semiconductor material, the wavelength of the light is the propagation wavelength of the light within the semiconductor material.

The thick dielectric material may have a thickness greater than λ/2, where λ is the wavelength of light in the thick dielectric material. The thick dielectric material may have a refractive index less than the refractive index of the semiconductor material and greater than or equal to 1. The light emitting semiconductor material may comprise, for example, aluminum gallium arsenide (AlGaAs), aluminum indium gallium phosphide (AlInGaP), aluminum indium gallium nitride (AlInGaN), and/or gallium arsenic phosphide (GaAsP). Other materials are equally suitable.

The light-transmissive thick dielectric material layer may be a relatively thick material such as silicon dioxide, silicon monoxide, magnesium fluoride (MgF)₂) And siloxane polymers, and/or air. Other materials are equally suitable.

The metal electrode and the semiconductorThere may be an ohmic contact layer therebetween. The ohmic contact layer may comprise, for example, Indium Tin Oxide (ITO), nickel oxide, and/or rhodium dioxide (RuO)₂). Other materials may also be suitable. The ohmic contact layer may be a portion of the semiconductor element having a heavily doped layer.

A current spreading layer may be disposed between the metal electrode and the semiconductor. The current-distributing layer is made of, for example, Indium Tin Oxide (ITO), nickel oxide or rhodium dioxide (RuO)₂) And (4) forming. Other materials may also be suitable.

One or more pairs of Distributed Bragg Reflector (DBR) dielectric layers in series may be formed between the thick dielectric layer and the metal electrode, each of the DBR dielectric layers of the pair being light transmissive and composed of layers of materials of different refractive index and/or thicknesses that approach an odd multiple of λ/4.

Each layer of the pairs of distributed Bragg reflectors may comprise, for example, titanium dioxide (TiO)₂) Titanium oxide (Ti)₃O₅) Titanium oxide (Ti)₂O₃) Titanium oxide (TiO), zirconium dioxide (ZrO)₂)、TiO₂ZrO₂Nb₂O₅Cerium oxide (CeO)₂) Zinc sulfide (ZnS), aluminum oxide (Al)₂O₃) Silicon nitride (SiN), Indium Tin Oxide (ITO), niobium pentoxide (Nb)₂O₅) Tantalum pentoxide (Ta)₂O_s) Siloxane polymers, silicon monoxide (SiO), silicon dioxide (SiO)₂) And/or magnesium fluoride (MgF)₂). Other materials are equally suitable.

The metal electrode may comprise one or more metal layers, wherein each metal layer is selected from the group consisting of: aluminum (Al), silver (Ag), rhodium (Rh), lead (Pd), copper (Cu), gold (Au), chromium (Cr), titanium (Ti), platinum (Pt), nickel/gold alloys, chromium/gold alloys, silver/aluminum mixtures, and combinations thereof. Other materials are equally suitable.

The LED may have a lateral or vertical structure. A portion of the metal electrode may form a wire bond region. A portion of the metal electrode may electrically contact the semiconductor material along an edge of the thick dielectric material. A portion of the metal electrode electrically contacts the semiconductor material through the opening in the thick dielectric material.

According to one embodiment of the present invention, a reflective electrode structure of a light emitting diode includes a metal electrode. A gallium nitride (GaN) material emits light having a central wavelength of about λ. A relatively thick silicon dioxide material may be formed on the gallium nitride (GaN) material. A portion of the electrode is formed over the thick dielectric material. Another portion of the electrode is in ohmic contact with a semiconductor material. The thick dielectric material has a thickness greater than λ/2. The dielectric material and the metal electrode are in physical contact with the semiconductor through an Indium Tin Oxide (ITO) layer or other material. Other materials are equally suitable.

According to one embodiment of the present invention, a reflective electrode structure includes a metal electrode and a gallium nitride (GaN) material that emits light having a center wavelength of about λ. A thick silicon dioxide material may be formed on the gallium nitride (GaN) material. At least one distributed bragg reflector pair is formed on the thick silicon dioxide material.

A portion of the electrode is formed over the thick dielectric material and the dbr pairs. Another portion of the electrode is in ohmic contact with the semiconductor material. The thick dielectric material may have a thickness greater than λ/2.

Each of the distributed bragg reflector pairs is light transmissive, each layer has a different refractive index, and the thickness of each distributed bragg reflector pair is an odd multiple of approximately λ/4. The dielectric material and the metal electrode are in physical contact with the semiconductor through an Indium Tin Oxide (ITO) layer.

Thus, according to one or more embodiments of the present invention, a brighter and/or more efficient LED is provided. Increasing the brightness and/or efficiency of LEDs may allow LEDs to be used in more applications, including general lighting.

The present invention will become more fully understood from the detailed description and the accompanying drawings.

Drawings

FIG. 1 is a schematic diagram showing the concept of critical angle (critical angle);

FIG. 2 is a perspective semi-schematic view of a present day side-view LED structure;

FIG. 3 is a perspective semi-schematic view of a conventional vertical LED structure;

FIG. 4A is a semi-schematic diagram showing the light reflection of a current GaN/Cr/Au (GaN/Cr/Au) interface;

FIG. 4B is a graph showing the reflectivity of FIG. 4A at different incident angles at the GaN/Cr/Au (GaN/Cr/Au) interface;

FIG. 5A is a semi-schematic diagram illustrating a present day electrode structure with an ohmic contact layer;

FIG. 5B is a semi-schematic diagram illustrating a present day electrode structure having an ohmic contact/current distribution layer;

FIG. 6A is a top semi-schematic view of a portion of a conventional LED die, showing a circular contact that may also be used as a bond pad;

FIG. 6B is a top half schematic view of a portion of a conventional LED die, showing a cross-shaped contact with a circular bond pad;

FIG. 6C is a top semi-schematic view of a portion of a conventional LED die, showing exemplary contact geometries suitable for use with larger LEDs and having a circular contact that may also be used as a bond pad;

FIG. 7A is a side semi-schematic view of a present day low aspect ratio electrode structure;

FIG. 7B is a side semi-schematic view of a high aspect ratio electrode structure;

FIG. 8A is a semi-schematic diagram of the light reflection of a present day silver interface;

FIG. 8B is a graph showing the reflectance of the silver interface of FIG. 8A at different angles of incidence;

FIG. 9A shows GaN/silicon dioxide/silver (GaN/SiO) of a vertical structure LED₂/Ag) semi-schematic of interfacial light reflection;

FIG. 9B shows the structure of FIG. 9A on GaN/silicon dioxide/silver (GaN/SiO)₂Ag) interface reflectivity chart under different incident angles;

FIG. 10A is a semi-schematic diagram showing the reflection of light at the present gallium nitride/Air (GaN/Air) interface;

FIG. 10B is a graph showing the reflectivity of FIG. 10A at different angles of incidence at the gallium nitride/Air (GaN/Air) interface;

FIG. 11A is a graph showing the results of the above-described process on gallium nitride/silicon dioxide (GaN/SiO)₂) Semi-schematic of interface light reflection, wherein the thick dielectric material is thick according to one embodiment of the present invention;

FIG. 11B shows the structure of FIG. 11A on a gallium nitride/silicon dioxide (GaN/SiO)₂) A reflectivity chart of the interface at different incident angles;

FIG. 12A is a semi-schematic view showing light reflection at a gallium nitride/Air/aluminum (GaN/Air/Al) interface according to one embodiment of the invention;

FIG. 12B shows the GaN/silicon dioxide/aluminum (GaN/SiO) film of FIG. 12A₂Al) interface, wherein the thickness of the silicon dioxide layer is less than or equal to 1.75 times the wavelength of the incident light according to one embodiment of the invention;

FIG. 12C shows the GaN/silicon dioxide/aluminum (GaN/SiO) film of FIG. 12A₂Al) interface with a reflectivity at different angles of incidence, wherein the thickness of the silicon dioxide layer is greater than 1.75 times according to one embodiment of the inventionThe wavelength of the incident light;

FIG. 13A is a semi-schematic diagram showing light reflection at a DBR formed from alternating layers of silicon dioxide (SiO)₂) Layer and titanium dioxide (TiO)₂) Layer composition;

FIG. 13B is a graph showing the reflectivity of the DBR of FIG. 13A at different incident angles according to one embodiment of the invention;

FIG. 14 is a graph showing reflectivity for different materials and different angles of incidence, according to one embodiment of the present invention;

FIG. 15A is a semi-schematic view showing a first exemplary embodiment of a floating electrode according to the present invention;

FIG. 15B is a semi-schematic view illustrating a second exemplary embodiment of a floating electrode in accordance with the present invention;

FIG. 15C is a semi-schematic view showing a third exemplary embodiment of a floating electrode in accordance with the present invention;

FIG. 15D is a semi-schematic view showing a fourth exemplary embodiment of a floating electrode in accordance with the present invention;

FIG. 15E is a semi-schematic view showing a fifth exemplary embodiment of a floating electrode in accordance with the present invention;

FIG. 15F is a semi-schematic view illustrating a sixth exemplary embodiment of a floating electrode in accordance with the present invention;

FIG. 16A is a semi-schematic view showing a first exemplary embodiment of a floating electrode with an ohmic contact layer according to the present invention;

FIG. 16B is a semi-schematic view showing a second exemplary embodiment of a floating electrode with an ohmic contact layer according to the invention;

FIG. 16C is a semi-schematic view showing a third exemplary embodiment of a floating electrode with an ohmic contact layer according to the invention;

FIG. 16D is a semi-schematic view showing a fourth exemplary embodiment of a floating electrode with an ohmic contact layer according to the invention;

FIG. 16E is a semi-schematic view showing a fifth exemplary embodiment of a floating electrode with an ohmic contact layer according to the invention;

FIG. 16F is a semi-schematic view showing a sixth exemplary embodiment of a floating electrode with an ohmic contact layer according to the invention;

FIG. 17A is a schematic cross-sectional view of a conventional side-structure LED;

FIGS. 17B to 17D are perspective semi-schematic views showing respective structures of some steps of the method of fabricating the LED in FIG. 17A;

FIG. 18A is a schematic cross-sectional view of a vertical structure light emitting diode according to one embodiment of the present invention;

FIGS. 18B to 18E are perspective semi-schematic views showing respective structures of some steps of the method for fabricating the LED in FIG. 18A;

FIG. 19A is a schematic cross-sectional view of a light emitting diode in a lateral configuration in accordance with one embodiment of the present invention;

FIGS. 19B to 19E are perspective semi-schematic views showing respective structures of some steps of the method for fabricating the LED in FIG. 19A;

FIG. 20A is a perspective semi-schematic view of another embodiment of a suspended structure according to one embodiment of the invention;

FIG. 20B is a perspective semi-schematic view of another embodiment of a suspended structure according to one embodiment of the invention;

FIG. 21A is a semi-schematic view of an exemplary embodiment of an elongated LED of the present invention;

FIG. 21B is a semi-schematic view of an exemplary embodiment of an elongated LED of the present invention;

FIG. 22A is a semi-schematic view of an exemplary embodiment of the present invention in an elongated LED;

FIG. 22B is a semi-schematic view of an exemplary embodiment of the present invention in an elongated LED;

FIG. 22C is a semi-schematic view of an exemplary embodiment of the invention in an elongated LED;

FIG. 23A is a semi-schematic view of an exemplary embodiment of an elongated LED of the present invention;

FIG. 23B is a semi-schematic view of an exemplary embodiment of an elongated LED of the present invention;

FIG. 23C is a semi-schematic view of an exemplary embodiment of an elongated LED of the present invention; and

fig. 24 is a semi-schematic view of an exemplary embodiment of the invention in an elongated led.

Reference numerals:

10-light emitting diode

11- -high refractive index medium

12- -medium of low refractive index

20-light emitting diode

21- - -p type layer

22-n type layer

23- -electrode

24- -electrode

26- -active zone

27-light-transmitting non-conductive substrate

28- -cutting out space

30-light emitting diode

31- -p type layer

32-n type layer

33- -electrode

36- -active zone

37- -conductive substrate

41- - -gallium nitride

42-chromium electrode

43- -gold electrode

44-gold/chromium metal electrode structure

46- -reflectance curve

47- -reflectance curve

48- -reflectivity curve

51-semiconductor material

52-ohmic contact

53- -metal contact

54- -contact structure

55-semiconductor

56-ohmic contact/current distribution layer

57-metal electrode

61-semiconductor

62- -electrode

63- -Cross contact

71-gallium nitride

72- -chromium electrode

73- -gold electrode

74-gold/chromium metal electrode structure

75- - -gallium nitride

76-chromium electrode

77- -gold electrode

81- -gallium nitride

82- -silver electrode

83- -reflectance curve

84- -reflectance curve

85- -reflectance curve

101-conductive support substrate

102- -silver metal layer

103-lambda/4 dielectric material

104-gallium nitride semiconductor

121-gallium nitride semiconductor material

131-gallium nitride semiconductor material

132- -silicon dioxide layer

141-gallium nitride (GaN) substrate

142 a-electrode

142b- -electrode

142c- -electrode

142d- -electrode

142e- -electrode

142f- - -electrode

143 a-air gap

143b- -air gap

143c- -thick air gap

143d- -thick silicon dioxide layer

143e- - -Thick SiO₂Block

143f- - -thick SiO₂Block

144-Indium Tin Oxide (ITO) layer

151- -reflectivity curve

152- -reflectivity curve

153- -reflectivity curve

161-semiconductor

162- -metal electrode

163- -thick dielectric layer

171-gallium nitride substrate

172- -thick dielectric silicon dioxide layer

173- -electrode

181-semiconductor material

182- -silicon dioxide layer

183- -layer of titanium dioxide

184- -electrode

185- -thick dielectric layer

191- -reflectivity curve

192- -reflectivity curve

193- -reflectivity curve

1001- -conductive extended electrode

1002- -thick dielectric layer

1003- -thick dielectric layer

1004- -cutting out space

1005- -electrically conductive extended electrode

1006- -wire bond pad

1007-routing bonding pad

1008- -semiconductor material

1091- -wire bonding pad

1091a- -wire bonding pad

1092- -wire bonding pad

1092 a-wire bonding pad

1092b- -wire bond pad

1093- -semiconductor layer

1094- -active zone

1096- -substrate

1097- -p type layer

1098-n type layer

1099- -cutting out space

1099a- -cutting space

1101- -thick dielectric layer

1102- -thick dielectric layer

1102 a-thick dielectric layer

1192b- -bonding pad

1201- -semiconductor material

1202- -thick dielectric layer

1203- -p type wire extension wire

1204- -Thick dielectric layer

1205- -extension wire

1217- -wire bonding pad

1218-wire bonding pad

1219- -wire bonding pad

1280-semiconductor material

1281- -cutting space

1283- -end

1220- -gap

1501-thick p-type pad dielectric layer

1502- -extension wire

1503- -thick n-type pad dielectric layer

1504- -to cut out space

1505- -extension conductor

1507-n type welding pad

1511- -bonding pad

1512-wire bond pad

1701-thick dielectric layer

1702- -extension wire

1801- -reflectivity Curve

1802- -reflectance Curve

1803- -reflectivity Curve

1804- -reflectivity curve

1805- -reflectivity Curve

1806- -reflectivity Curve

1807- -reflectivity Curve

1901- -reflectance Curve

1902- -reflectance curve

1903- -reflectance Curve

1951- -reflectivity Curve

1952- -reflectivity Curve

1953- -reflectivity Curve

1954- -reflectivity Curve

1955- -reflectivity Curve

2401-semiconductor material

2402- -cutting out a space

2403- -n type welding pad

2404- -p type bonding pad

2406- -thick dielectric layer

2407- -Thick dielectric layer

Detailed Description

Light Emitting Diodes (LEDs) radiate light in response to excitation caused by electrical current. A typical LED utilizes organometallic vapor phase epitaxy or similar techniques to grow a heterostructure (heterostructure) on a substrate. An LED heterostructure includes n-type and p-type semiconductor layers sandwiching a light emitting layer such as an active region. An exemplary active region may be a quantum well surrounded by a barrier layer. Typically, electrical contacts are attached to the n-type and p-type semiconductor layers. When a forward bias is applied across the electrical contacts, electrons and holes flow out of the n-type and p-type layers to generate light in the active region.

The electrical conversion efficiency of an LED is determined by the product of internal quantum efficiency, light extraction efficiency and losses due to resistance. The internal quantum efficiency is determined by the quality of the semiconductor layer and the band structure of the device. Both of which are determined by the deposition of the semiconductor layer.

The light extraction efficiency is the ratio of the light leaving the LED chip to the light generated by the active region. The light extraction efficiency is determined by the geometry of the LED, the light absorption of the semiconductor layers by self-absorption, the light absorption of the electrical contacts, and the light absorption of the materials used to encapsulate a device in contact with the LED.

The semiconductor layers tend to have relatively high refractive indices. Thus, most of the light generated from the LED active region undergoes multiple internal reflections at the wafer surface before leaving the wafer. To improve light extraction efficiency, it is important to reduce the absorption of the semiconductor layer and the absorption due to electrical connections to the wafer. While these layers can be made to have very low light absorption, by having optical transparency or high reflectivity, substantially the overall LED light extraction efficiency can be improved.

Referring to fig. 1, light is directed from within a high refractive index medium 11 to the interface with a low refractive index medium 12. The light rays may have different angles of incidence. When the light encounters an interface with a low-refractive-index medium 12 from a high-refractive-index medium 11, the light either penetrates into the low-refractive-index medium 12 or is reflected back into the high-refractive-index medium 11.

According to Snell's law, a portion of a light ray propagates from a material with refractive index n1 into a material with lower refractive index n2, where the light ray can enter the material with lower refractive index at an incident angle less than the critical angle θ c. The arrows on the left indicate that the light is continuous from the material with refractive index n1 into the material with the lower refractive index n 2.

Conversely, according to Snell's law, light travels from a material with refractive index n1 into a material with a lower refractive index n2, and at incident angles greater than the critical angle θ c, all of the light is reflected back into the material with the higher refractive index. This mechanism is known as Total Internal Reflection (TIR), and the right arrow indicates that light is not continuous from a material with a high refractive index n1 into a material with a lower refractive index n2, but instead extends back into the material with the high refractive index.

Light is totally internally reflected within a high refractive index material having a higher refractive index than the external material (e.g., light in a semiconductor material, air or an epoxy encapsulation being the external material) when it strikes the interface at an angle of incidence greater than the critical angle thetac. Typical semiconductor materials have a refractive index that is higher than that of ambient air (refractive index equal to 1) or epoxy encapsulation (which may have a refractive index close to 1.5).

In an LED, light reflected back to the LED chip is further absorbed by other materials. This undesired absorption reduces the amount of light that the LED can provide and reduces the efficiency of the LED.

With conventional LEDs, most of the light generated within the structure undergoes total internal reflection when it leaves a semiconductor wafer. For gallium nitride (GaN) LEDs, which are conventionally fabricated on sapphire substrates, approximately 70% of the light is confined between the sapphire substrate and the outer surface of the GaN (GaN). The light rays are repeatedly reflected by total internal reflection and are thus absorbed multiple times by the metal electrodes or other materials. It is therefore highly desirable to create a structure that minimizes this absorption.

As used herein, an electrode refers to a conductor (e.g., a metal conductor) that provides current to the semiconductor material of an LED. Thus, the electrode may electrically contact the semiconductor material. However, not all parts of the electrode need to be in electrical contact with the semiconductor material. In fact, according to one or more embodiments of the present invention, a portion of the electrodes is used to electrically contact the semiconductor material, and another portion of the electrodes is not electrically contacted with the semiconductor material.

Referring now to fig. 2, there is shown a present day side-structure LED. Electrodes 23 and 24 are formed on the surfaces of a p-type layer 21 and an n-type layer 22 of the light emitting diode 20 by metallization. A p-n junction or active region 26 is between the p-type layer 21 and the n-type layer 22. The electrodes 23 and 24 provide a path for providing electrical energy to the led 20. The semiconductor of the device structure may be supported by a light-transmissive non-conductive substrate 27, the substrate 27 comprising a material such as sapphire, and the electrical contacts for the p-type layer 21 and the n-type layer 22 must be made at the top surface of the device.

In the structure shown in fig. 2, the p-type layer 21 has been exposed on the top surface of the structure, on which electrical contacts can be easily made. However, the n-type layer 22 is buried under the p-type layer 21 and the active region 26. To make electrical contact to the n-type layer 22, a portion of the p-type layer 21 and the active region 26 (the removed portion is shown by the dotted lines) are removed to form a divot space 28 to expose the underlying n-type layer. After the cut-out space 28 is made, the n-type layer electrical contact or electrode 24 may be formed.

Such a device structure as shown in fig. 2 causes current to flow substantially in the lateral direction. This is why they are called lateral structures. One disadvantage of this lateral structure is that a portion of the light emitting region must be removed to create the cutout space 28 so that the n-type electrode 24 can be formed. Of course, this reduces the area of the active region and thus the ability of the led 20 to generate light.

Referring now to fig. 3, another alternative led 30 structure is shown in which the semiconductor, including a p-type layer 31 and an n-type layer 32 together defining an active region 36, is supported by a conductive substrate 37. The substrate 37 may be made of a light-transmitting conductive material such as silicon carbide (silicon carbide), or an opaque conductive material such as copper or molybdenum. The light emitting diode can be fabricated with the n-type layer or the p-type layer in contact with the substrate.

In the light emitting diode, the conductive substrate 37 may be provided as one electrode, and the other electrode 33 may be easily formed on the top surface, for example, the top surface of the p-type layer 30. Because the contacts or electrodes are on opposite surfaces of the led 30, current flows in a substantially vertical direction. Such a device structure is therefore referred to as a vertical structure.

The same requirements are satisfied for the metal electrodes, whether they are vertical or lateral led structures. These requirements include good adhesion, the ability to have ohmic contacts to the semiconductor, good conductivity, and good reliability. Generally, these requirements can be met by using two or more layers of material. For example, a first metal layer such as chromium or titanium may provide good adhesion and ohmic contact. A second metal layer such as silver or gold may provide good conductivity.

While chromium has good adhesion and gold is a good conductor, neither of these materials has good light reflectivity in the visible range. The light reflectivity and its corresponding light absorption can be calculated from the refractive indices of the structures and their corresponding thicknesses.

Here, no thickness of material is provided, which can be assumed to be sufficiently large, so that the optical interference phenomenon may be disregarded. For example, the reflectivity calculation typically assumes that the entrance and exit media are semi-infinite (semi-infinite). In the case of metal reflective layers of unspecified thickness, it is assumed that they are thick enough, typically thousands of nanometers, so that very little light will reach the other side of the metal. The index values of Table one are used to calculate all the reflectance curves of the present invention.

Table one

The thickness of the materials disclosed herein may be expressed in absolute units, TABS, such as microns or nanometers. Alternatively, the thickness of the material can also be expressed as a relative multiple of the wavelength of light in the medium, TlRel. This parameter specifically corresponds to the wavelength of light in a given material when the thickness of the material is a multiple of a wavelength (λ). The absolute thickness can be calculated by dividing the parameter by the refractive index of the material by equation one below. For example. A lambda/4 silica will be 76.8 nm (0.25.450/1.465) at 450 nm.

TABS ═ λ Rel/N λ (formula one)

The light reflectance curve has two components as a function of incident angle, P-polarized light and S-polarized light. P-polarized light is sensitive to Brewster' S angle, and therefore has a lower overall reflectance than S-polarized light.

Referring now to fig. 4A, a present semiconductor and electrode structure diagram shows an electrode 44 reflecting light from the semiconductor 41. The electrode is formed on a gallium nitride (GaN) semiconductor 41 using a typical electrode combination of chromium 42 and gold 43. Light incident at 45 degrees produces a reflection, with only 25% of the P-polarized and S-polarized light being reflected on average, and 75% being absorbed. Thus, the current electrode assembly structure has undesirably high absorption.

Although fig. 4A shows a gold/chromium metal electrode structure formed on gallium nitride (GaN), other metal or semiconductor materials may alternatively be utilized.

Referring now to fig. 4B, a graph shows the reflectivity of the device of fig. 4A at different angles of incidence at the gallium nitride/chromium/gold (GaN/Cr/Au) interface.

Referring now to FIG. 5A, a more general present day contact structure is shown. According to this more general contact structure, an ohmic contact and/or current spreading layer (52) may be interposed between a metal contact 53 and a semiconductor material 51. The metal contact 53 may have multiple layers for adhesion, diffusion barrier, solder ball, conductivity, and ohmic contact purposes. The layers may be made of various metals or combinations of metals including nickel, platinum, titanium, silver, aluminum, gold, tin, lead, and chromium. The semiconductor 51 may be derived from material systems such as aluminum gallium arsenide (AlGaAs), aluminum gallium indium phosphide (AlInGaP), aluminum gallium indium nitride (AlInGaN), and gallium arsenic phosphide (GaAsP). The ohmic contact layer may be part of the metal electrode layers such as nickel oxide.

Referring now to fig. 5B, a conductive metal oxide such as Indium Tin Oxide (ITO) or nickel oxide may be deposited over the entire surface of the semiconductor 55 to define an ohmic contact/current distribution layer 56 on which a metal electrode 57 is formed. In this case, the ohmic contact/current distribution layer 56 is used as an ohmic contact and a current distribution layer. There may be a layer that allows ohmic contact to be made to the top surface of the led semiconductor material, such as a heavily doped region.

Despite the precise metal electrode configuration, semiconductor material, or led structure, current metal electrodes may undesirably absorb some light. Furthermore, the metal contacts are not transparent to light, and they block a portion of the surface area from which light is removed. Thus, the current electrode has a dual effect. They not only directly absorb part of the incident light, but the rest of the reflected light is reflected back into the element and is absorbed again by other materials. The amount of light absorption is highly dependent on the actual structure of the electrode and tends to be proportional to the size of the electrode contact area.

Referring now to fig. 6A-6C, a current distribution principle for alleviating the current crowding problem will be discussed. The p-type and n-type layers of current leds are thin and have relatively low conductivity. Thus, these layers do not uniformly distribute current to all regions of the p-n junction, such as the active region. For larger areas, a portion of the active region is away from the electrode, so that less current flows in the more distant regions than in the less distant regions. This results in an uneven current distribution and an uneven emitted light. To reduce current crowding, the geometry of the metal electrodes is extended to the entire surface of the semiconductor. However, these extensions can lead to additional unwanted light absorption.

Referring to fig. 6A, a circular contact or electrode 62 may be formed on a semiconductor 61 and may be considered a wire bond pad. Referring to fig. 6B, a cross-shaped contact 63 may be combined with the electrode 62 to enhance current distribution. Referring to fig. 6C, other different geometries 63 may also be incorporated with the electrodes 62 to facilitate current distribution, particularly over larger size led dies.

Generally, wire bonding is used as a means to provide electrical power to the leds. However, the minimum dimension of the wire bond pad area is approximately 100 microns x100 microns. The size of each wire bond pad is fixed regardless of the device size, and the light-absorbing and light-impermeable wire bond pad area occupies a large portion of the surface area of the led.

One way to reduce the undesirable absorption of light by the electrodes is to minimize the contact area or electrode width. If electrical connection to the led semiconductor material is the only consideration, the width of the contact may be relatively small, e.g., on the order of a few microns. However, reducing the cross-sectional area increases the unwanted resistance. In high power applications, the electrode may carry a current of 1 amp or more. This requires a cross-sectional size with a width (W) x a thickness (T) with a certain minimum value to minimize the resistance value. Therefore, it is not possible to merely reduce the contact area or the width of the electrode without compensating for the increased electrode resistivity.

Referring now to fig. 7A, a gold electrode typically measures 20 microns W and 2 microns T and has a total cross-sectional area of 40 square microns. In theory, increasing the thickness and decreasing the width in the proper proportion is one way to maintain a constant cross-sectional area and constant resistance, as discussed below with reference to FIG. 7B.

Referring now to fig. 7B, according to one embodiment of the invention, the aspect ratio (aspect ratio) of electrode 77 may be increased. The height of the electrode 77 may be increased relative to its width. For example, the height may be increased to provide a thickness greater than 2.5 microns. In this manner, the area of the electrode 74 that contacts the semiconductor 75 (and thus causes light absorption) is reduced resulting in a similar reduction in light absorption. Increasing the height of the electrode 77 maintains the desired conductivity. The contact area is reduced and the thickness of the electrode is increased to maintain the desired conductivity. However, manufacturing costs and practical process considerations typically limit the thickness of the electrode to 2.5 microns or less. If the electrode is used only as an electrical contact for the semiconductor material, the electrode contact area and its accompanying absorption will become much larger than actually required.

Another way to reduce the absorption of the electrode is to increase the reflectivity of the electrode. Some prior art approaches have been used to fabricate the reflective electrodes of light emitting diodes. The simplest approach is to use a metal with high reflectivity. These metals include aluminum, silver, rhenium, and other metals known to those skilled in the art.

The metal selected is not only required to have a high reflectivity but also an acceptable low resistance ohmic contact to the semiconductor material. In the case of p-type indium gallium nitride aluminum (AllnGaN), only silver has a low resistance value and a high reflectance.

Referring to fig. 8A, a metal electrode structure of silver is shown. A silver electrode 82 is formed on a semiconductor substrate 81. Unfortunately, silver is tarnished during device operation and suffers from electron migration (electron migration) causing reliability problems. Also, the contact resistance of the silver-based material contact sometimes increases with time during the operation of the element.

Referring now to fig. 8B, the reflectance of the silver electrode of fig. 8A at different angles of incidence is shown. Even with highly reflective metal electrodes, silver, the absorption per reflection near normal incidence is nearly 10%. It would therefore be highly desirable to further reduce the absorption to below 10%.

Referring now to fig. 9A, it is known to use a layer of λ/4 dielectric material 103, such as silicon dioxide, to increase the reflectivity of a vertical structure led. The dielectric material 103 is formed between a gallium nitride (GaN) semiconductor 104 and a silver metal layer 102, both of which are formed on a conductive support substrate 101. However, as discussed below, the use of a λ/4 dielectric material does not substantially increase the reflectivity.

Referring now to fig. 9B, it can be seen that the use of the λ/4 dielectric material layer does provide increased reflectivity for incident S-polarized light, as shown by curve 153. However, the reflection curve for P-polarized light incident on the dielectric material layer at about 47 degrees has a depth drop, as indicated by curve 152. Curve 151 indicates the average reflectivity for S-polarized light and P-polarized light, and this depth reduction substantially reduces the overall reflectivity. Therefore, the use of a λ/4 dielectric material layer is not a suitable solution to the problem of light absorption by the led electrodes.

According to one embodiment of the present invention, a reflective electrode structure minimizes the contact area between the electrode and the led semiconductor material. A relatively thick dielectric material is disposed between a conductive electrode and the semiconductor material to electrically insulate portions of the electrode while allowing other portions of the electrode to electrically contact. The dielectric material may have a lower refractive index than the semiconductor and a sufficient thickness such that total internal reflection (total internal reflection) may occur at an angle of incidence greater than the critical angle Θ c, as discussed below.

Total internal reflection of the dielectric material provides the desired reflectivity of approximately 100%. Total internal reflection occurs above the critical angle Θ c. In the case of gallium nitride and air interfaces, the critical angle is close to 24 degrees. In the case of an interface of gallium nitride and silicon dioxide, the critical angle is close to 37 degrees.

Referring now to FIG. 10A, a semi-schematic view of light reflected at the GaN/air interface is shown. Since the incident angle is larger than the critical angle Θ c, a light ray is reflected back to the gan semiconductor material 121 at the interface.

Referring now to fig. 10B, the reflectance at different light incidence angles for the gallium nitride/air interface of fig. 10A is shown.

Referring now to fig. 11A, shown is a semi-schematic diagram of light reflection at a gallium nitride/silicon dioxide interface in accordance with one embodiment of the present invention. Since the incident angle is larger than the critical angle Θ c, the light is reflected back to the gan semiconductor material 131 at the interface between the semiconductor material 131 and the silicon dioxide.

Referring now to FIG. 11B, the reflectivity of FIG. 11A at different angles of incidence of the GaN/silicon dioxide interface is shown, in accordance with one embodiment of the present invention.

Referring now to FIG. 12A, a diagram illustrating light in gallium nitride/silicon dioxide/aluminum (GaN/SiO) is shown, in accordance with one embodiment of the present invention₂Al) semi-schematic of the interface reflection. A portion of the electrode 173 is suspended above the gan substrate 171 and a thick dielectric material, silicon dioxide (SiO)₂) With layer 172 formed therebetween. Another portion of the electrode 173 is formed directly on the gan layerOn a substrate 171.

Referring now to fig. 12B, there is shown the reflectance at different angles of incidence of the gallium nitride/silicon dioxide/aluminum interface of fig. 12A for a thickness of the silicon dioxide layer less than or equal to 1.75 times the wavelength of the incident light, in accordance with one embodiment of the present invention. There is no total internal reflection in the case of lambda/16 silica and the reflectivity is slightly worse than without this silica layer. In the case of lambda/4 silicon dioxide, there is no total internal reflection and its reflectivity is rather poor. In the case of λ/2 silica, there is a total internal reflection at high angles of incidence, but a substantial reduction in reflectivity occurs near 38 degrees. At 1.75 λ, total internal reflection occurs at high angle incidence without significant reduction in reflectivity. Because total internal reflection begins to occur at λ/2 silicon dioxide, the "thick" dielectric material refers to all dielectric materials having a thickness greater than λ/2 or equal to λ/2.

Referring now to fig. 12C, the reflectivity at different incident angles of the gan/si/al interface of fig. 12A is shown for a silicon dioxide layer thickness greater than 1.75 times the wavelength of the incident light according to one embodiment of the present invention.

Once the dielectric layer is greater than the minimum thickness for total internal reflection, its exact thickness is no longer as critical as conventional optical coatings based on the principle of interference, allowing a greater range in the manufacturing process. FIG. 12C shows the reflectance curve for a thick dielectric layer at two different thicknesses, one at 1.75 λ and the other at 1.85 λ. The angle of total internal reflection is not changed.

Referring now to FIG. 13A, a semi-schematic diagram of light reflection at a DBR formed from alternating layers of silicon dioxide (SiO)₂) Layer 182 and titanium dioxide (TiO)₂) Layer 183 is compositionally formed on the thick silicon dioxide dielectric substrate layer 185. An electrode 184 electrically contacts the semiconductor material 181 and is the last layer above the dbr layer. The thick dielectric layer 185 is between the dbr stack and the semiconductor material 181.

The thick dielectric layer acts as an effective reflector at large angles. However, it does not substantially enhance the reflectivity at incident angles below the critical angle. A Distributed Bragg Reflector (DBR) may be added to increase light reflection at lower angles of incidence. Distributed Bragg Reflectors (DBRs) are typically made using a series of alternating high/low index dielectric materials. As shown in FIG. 13A, a series of two pairs of λ/4 silicon dioxide (SiO)₂) And lambda/4 titanium dioxide (TiO)₂) Over a 1.75 lambda thick layer of silicon dioxide to increase reflection at low incidence. DBRs use the principle of optical interference to affect reflections so that the accuracy of their thickness is more important than the thickness of the thick layer of silicon dioxide below it.

Table two below provides more information on electrode materials according to one or more embodiments of the present invention. The reference wavelength of the thickness of the plating film was 0.45 μm. The phase and delay values are in degrees. The coating has six layers. The incident medium is gallium nitride (GaN). The wavelength of light used was 0.45 microns.

Table two

Material	Thickness of
		Al1	1.000000
SiO2	0.250000
		TiO2	0.250000
SiO2	0.250000
		TiO2	0.250000
SiO2	0.750000

Referring now to FIG. 13B, therein is shown the reflectivity of FIG. 13A at different angles of incidence of the DBR compared to a design with only a thick dielectric layer and compared to a design without a thick dielectric layer and without a DBR, in accordance with one embodiment of the present invention.

Referring now to FIG. 14, therein is shown reflectivity for different materials and different angles of incidence compared to the prior art, in accordance with one embodiment of the present invention. A gold metal layer having a chromium layer with the worst reflectivity below it is shown by the lowest curve 1951. The reflectivity of aluminum is substantially better as shown by curve 1952. The reflectance of silver is better as shown by curve 1953. A silver metal layer has a thick dielectric layer of silicon dioxide under which there is substantially better reflectivity than silver, although curve 1954 has a lower sag in some places than curve 1953. A silver metal layer with two DBR pairs with a thick layer of silicon dioxide with optimal reflectivity is shown in curve 1955.

Referring now to fig. 15A, a semi-schematic view of a first exemplary embodiment of a suspended electrode according to the present invention is shown. The electrode 142a is suspended above a gallium nitride (GaN) substrate 141 with a thick air gap 143a formed therebetween. The electrode 142a is supported on both sides thereof.

Referring now to FIG. 15B, a semi-schematic view of a second exemplary embodiment of a floating electrode according to the present invention is shown. The electrode 142b is suspended above a gallium nitride (GaN) substrate 141 such that a plurality of air gaps 143b are formed therebetween. The electrode 142a is supported on both sides and in the middle thereof.

Referring now to FIG. 15C, a semi-schematic view of a third exemplary embodiment of a floating electrode according to the present invention is shown. The electrode 142c is suspended above a gallium nitride (GaN) substrate 141 such that a thick air gap 143c is formed therebetween. The electrode 142c is supported only on one side thereof.

Referring now to FIG. 15D, a semi-schematic view of a fourth exemplary embodiment of a floating electrode according to the present invention is shown. The electrode 142d is suspended above a gan substrate 141 with a thick silicon dioxide layer 143d formed therebetween. The electrode 142d is supported on both sides thereof.

Referring now to FIG. 15E, a semi-schematic view of a fifth exemplary embodiment of a floating electrode according to the present invention is shown. Electrode 142e is suspended above a GaN substrate 141 and has a plurality of thick SiO layers₂The block 143e is formed therebetween. The electrode 142e is supported on both sides and in the middle thereof.

Referring now to FIG. 15F, a semi-schematic view of a sixth exemplary embodiment of a floating electrode according to the present invention is shown. Electrode 142f is suspended above a gallium nitride (GaN) substrate 141 such that a thick SiO layer is formed₂With a layer 143f formed therebetween. The electrode 142d is supported on only one side thereof.

Referring now to FIG. 16A, a semi-schematic view of a first exemplary embodiment of a floating electrode having an ohmic contact layer is shown. The electrode structure of fig. 16A is similar to that of fig. 15A, except that an Indium Tin Oxide (ITO) layer 144 is added.

Referring now to FIG. 16B, a semi-schematic view of a second exemplary embodiment of a floating electrode having an ohmic contact layer is shown. The electrode structure of fig. 16B is similar to that of fig. 15B, except that an Indium Tin Oxide (ITO) layer 144 is added.

Referring now to FIG. 16C, a semi-schematic view of a third exemplary embodiment of a floating electrode with an ohmic contact layer is shown. The electrode structure of fig. 16C is similar to that of fig. 15C, except that an Indium Tin Oxide (ITO) layer 144 is added.

Referring now to FIG. 16D, a semi-schematic view of a fourth exemplary embodiment of a floating electrode with an ohmic contact layer is shown. The electrode structure of fig. 16D is similar to that of fig. 15D, except that an Indium Tin Oxide (ITO) layer 144 is added.

Referring now to FIG. 16E, a semi-schematic view of a fifth exemplary embodiment of a floating electrode having an ohmic contact layer is shown. The electrode structure of fig. 16E is similar to that of fig. 15E, except that an Indium Tin Oxide (ITO) layer 144 is added.

Referring now to FIG. 16F, a semi-schematic view of a sixth exemplary embodiment of a floating electrode having an ohmic contact layer is shown. The electrode structure of fig. 16F is similar to that of fig. 15F, except that an Indium Tin Oxide (ITO) layer 144 is added.

Referring now to fig. 17A-17D, a conventional lateral led structure and process steps are shown.

Referring to fig. 17A, a pair of wire bond pads 1091 and 1092 facilitate current flow to a semiconductor 1093. The semiconductor 1093 is formed on a substrate 1096. The semiconductor 1093 includes a p-layer 1097 and an n-layer 1098 (n-layer 1098 and p-layer 1097 are typically interchanged). The current causes the active region 1094 to generate light in accordance with known principles.

Referring to fig. 17B, the led fabrication of fig. 9A includes forming a semiconductor layer 1093 on a substrate 1096. The semiconductor layer 1093 includes an n-layer 1098 and a p-layer 1097 (shown in fig. 17A).

Referring to fig. 17C, a portion of the p-type layer 1097 is removed, such as by an etching technique. A sufficiently large portion of p-layer 1097 is removed to expose an underlying portion of n-layer 1098. The removed portion of the p-type layer defines a cut-out space (cut out portion) 1099. The cut-out space 1099 is formed to expose the n-type layer 1098.

Referring to fig. 17D, wire bond pad 1091 is formed on p-layer 1097 and wire bond pad 1092 is formed on n-layer 1098. Wire bond pad 1091 and wire bond pad 1092 cover a substantial portion of the surface area of semiconductor 1093. For example, the electrode bonding pads of a current led can be 100 microns x100 microns. They absorb a significant amount of light generated from the active region 1094. Further, the larger cut-out space 1099 is used for a wire bond pad 1092 to reduce the size of the active region 1094 and further reduce the light output of the conventional led. The dimensions of the electrode are fixed regardless of the size of the element, and the aforementioned undesirable light absorption may be a large fraction of the total surface area, particularly for smaller size leds.

It is noted that the electrode structure with a portion of the electrode inside the cutout space and a portion of the electrode outside the cutout space provides substantial advantages even if the electrode is not light reflective. For example, the electrode structure as described in fig. 18A-18B below provides sufficient wire bond area while minimizing the amount of the cut-out space so that less active area is removed and more light is generated.

Referring now to fig. 18A-18E, an exemplary present day lateral light emitting diode structure and process thereof is shown, in accordance with one embodiment of the present invention. A thick dielectric layer 1101 and 1102 is formed under wire bond pads 1091a and 1092a, respectively. Thick dielectric layers 1101 and 1102 enhance the reflectivity of wire bond pads 1091a and 1092a so that undesirable light absorption can be substantially reduced. A portion of each wire bond pad 1091a and 1092a remains in contact with semiconductor 1093 to facilitate current flow.

As used herein, a thick dielectric layer refers to a dielectric layer having a sufficient thickness such that interference is not critical. Furthermore, a thick dielectric layer used herein may have a thickness greater than λ/4. For example, a thick dielectric layer may have a thickness equal to or greater than λ/2, or close to 1.5 λ, or close to 1.75 λ, or greater than 1.75 λ.

Referring to fig. 18B and 18C, a semiconductor 1093 is formed over the substrate 1096 and cut-out spaces 1099 are formed in the semiconductor 1093 as shown in fig. 187 and 17C.

Referring to fig. 18D, thick dielectric layers 1101 and 1102 are formed on p-type layer 1097 and n-type layer 1098, respectively. Thick dielectric layers 1101 and 1102 may be formed according to known principles.

Referring to fig. 18E, wire bond pad 1091a is formed at least partially overlying thick dielectric layer 1101, and wire bond pad 1092a is formed at least partially overlying thick dielectric layer 1102. As noted above, a portion of wire bond pads 1091a and 1092a contact underlying semiconductor 1093.

Referring now to fig. 19A-19E, therein are shown exemplary lateral light emitting diode structures and processes thereof, according to one embodiment of the invention.

Referring now to fig. 19A, a thick dielectric layer 1101 and 1102a is formed under wire bond pads 1091a and 1092b, respectively. Thick dielectric layers 1101 and 1102a enhance the reflectivity of wire bond pads 1091a and 1092b such that the unwanted light absorption can be substantially reduced. Each wire bond pad 1091a and 1092b remains in contact with semiconductor 1093 to facilitate current flow.

Referring to fig. 19B and 19C, a semiconductor 1093 is formed over the substrate 1096 and a cutout 1099a is formed in the semiconductor 1093 as shown in fig. 17B and 17C. However, in this embodiment, the cut-out space 1099a is formed in an L-shaped configuration to reduce the surface area thereof. In this way, the cut-out space 1099a is formed such that less active area is sacrificed and the brightness of the led is increased.

Referring to fig. 19D, a thick dielectric layer 1101 is formed on the p-type layer 1097. Another thick dielectric layer 1102a is formed partially on p-layer 1097 and partially on n-layer 1098. Thick dielectric layers 1101 and 1102a may be formed according to known principles. In this example, thick dielectric layer 1102a extends down the edges of p-layer 1097 and active region 1094 to electrically isolate wire bond pad 1092 b. That is, thick dielectric layer 1102a is formed on and at the interface between p-type layer 1097 and n-type layer 1098, such as active region 1094. Thick dielectric layer 1102a is stepped down from p-layer 1097 to n-layer 1098. The structure of thick dielectric layer 1102a can be clearly seen in the cross-sectional structure of fig. 19A.

Referring to fig. 19E, wire bond pad 1091a is formed at least partially over thick dielectric 1101 and wire bond pad 1092b is formed at least partially over thick dielectric 1102 a. As mentioned above, a portion of wire bond pad 1091a contacts p-layer 1097 and a portion of wire bond pad 1092b contacts n-layer 1098. In this case, wire bond pad 1092b is formed down and separated by thick dielectric 1102a and covers thick dielectric 1102a and electrically contacts n-layer 1098. The configuration of wire bond pad 1092b is best seen in fig. 19A.

In this embodiment, thick dielectric layers 1101 and 1102a substantially reduce the light absorption of wire bond pads 1091a and 1092b, thereby increasing the brightness of the led. Reducing the size of the cut-out space 1099a provides a larger active region 1094, thereby further increasing the brightness of the led.

According to the present invention, a thick dielectric layer may be formed between at least a portion of each wire bond pad and/or electrode and the semiconductor material. The thick dielectric material enhances reflectivity such that unwanted light absorption by the bond pads and/or electrodes is substantially reduced.

Referring now to fig. 20A, a perspective semi-schematic view of one embodiment of a floating electrode structure in accordance with one embodiment of the present invention. A metal electrode 162 is formed on a semiconductor 161. A thick dielectric layer 163 is formed between the metal electrode 162 and the semiconductor 161. A portion of electrode 162 is formed on thick dielectric layer 163 and a portion of electrode 162 contacts semiconductor 161 so that electrode 162 electrically contacts semiconductor 161.

Referring now to FIG. 20B, shown is a perspective semi-schematic view of another floating electrode configuration in accordance with one embodiment of the present invention. This structure is substantially similar to that of fig. 20A except that the thick dielectric layer 163 is segmented so as to contact the semiconductor at a different location than the partial electrode 162 of fig. 20A. As shown in fig. 20B, the electrode 162 makes multiple contacts with the semiconductor 161. As will be appreciated by those skilled in the art, different configurations of the electrode 162 and the thick dielectric layer 163 are possible to have the electrode 162 contact the semiconductor 161 at various locations.

Fig. 21A-24 illustrate an exemplary electrode structure utilizing a thick dielectric layer in accordance with one or more embodiments of the present invention. For example, one or more insulating dielectric layers may be formed under the wire bond pads. The advantages of this structure include: current crowding is reduced, thereby facilitating a simple design; since the dielectric layer(s) under the electrodes can form a mirror, light absorption is minimized; the light emitting region can be utilized more efficiently by reducing the cutting space; for a wide range of grain sizes, a design that changes size more easily; a lower forward bias; more uniform current distribution.

The exemplary embodiment of fig. 21A-24 is an elongated wafer (elongated chip) embodiment. The elongated chip provides enhanced brightness and better efficiency.

Referring now to fig. 21A, an electrode design for an elongated wafer is shown. Thick dielectric layers 1002 and 1003 can be formed under wire bond pad 1006 (e.g., the p-pad) and under wire bond pad 1007 (e.g., the n-pad). An n-type pad 1007 and an n-type electrode extension electrode 1001 are formed on the etch-removed portion or cut-out space 1004 of semiconductor material 1008.

Thick dielectric layers 1002 and 1003 insulate bond pads 1006 and 1007 from semiconductor material 1008 to alleviate current crowding. Such an improved geometry may result in more uniform current flow. Hot spots that cause uneven brightness and may damage the led are substantially reduced.

The thick dielectric layers are not formed under the conductive extension electrodes 1001 and 1005 that define the n-type and p-type conductive lines, respectively. The conductive extension electrodes 1001 and 1005 can thus more evenly distribute current to the entire semiconductor 1008. According to an aspect of the present invention, the distance between the electrodes providing current to the light emitting diode can be more uniform.

It is noted that total internal reflection provides a substantial advantage in increasing the light extraction efficiency of one or more embodiments of the present invention. According to at least one embodiment of the present invention, a DBR structure may be optionally used to further increase the light extraction rate.

The use of total internal reflection and/or DBR structures as described above substantially reduces the unwanted absorption of light by wire bond pads 1006 and 1007. Such insulators (e.g., insulating layers 1002 and 1003) may be formed under bond pads 1006 and 1007 rather than under extension electrodes 1001 and 1005 so that the current flowing through the semiconductor (and its active region) is more evenly distributed.

As shown in fig. 21A and 21B, wire bond pads 1006 and 1007 are not precisely located at an end of the conductive lines or extension electrodes 1001 and 1005. The wire bond pads 1006 and 1007 can be placed at any location along the conductive lines. Thus, bond pads 1006 and 1007 can be disposed at the ends, near the ends, and/or in the middle of extension electrodes 1001 and 1005. The present invention can be used with any location where bond pads 1006 and 1007 are located.

Referring to fig. 21B, a possible modification of the structure of fig. 21A is shown. The area of the cut out space 1104 is reduced by placing the n-type bond pad on the p-type surface and separating it from the p-type surface by the thick dielectric layer. That is, at least a portion of the n-type pad is not located in the cut-out space 1104, and therefore the cut-out space 1104 may be smaller than the cut-out space of fig. 21A. This thick dielectric layer must also cover the edges of the cut-out space to keep the n-type pad insulated from the p-type layer. That is, the area of the cut-out space is reduced to increase the area of the active region. Utilizing a smaller cutout 1004 to produce a larger light emitting area may allow for greater power output.

In some applications, the distance between the n-type and p-type electrodes may be too large, resulting in an undesirably high forward bias. In these cases, it is advantageous to use a plurality of electrodes. FIGS. 22A-23C illustrate various exemplary implementations of three electrode designs that reduce the unwanted high forward bias.

Referring now to fig. 22A-22C, the n-type bond pad is shown separated into two electrically independent bond pads 1217 and 1218. In principle, they can be in contact with each other (and thus electrically) and thus form a single wire bond pad. The present invention may have two separate wire bonds, one for each of wire bond pads 1217 and 1218. However, if gap 1220 between bond pads 1217 and 1218 is small enough, a single bond pad can be used to electrically connect bond pads 1217 and 1218 together. Under this rule, any desired number of electrodes may be used.

Referring to fig. 22A, two n-type bond pads 1217 and 1218 and a single p-type bond pad 1219 are shown as being used. Two thick dielectric layers 1204 and 1283 may be formed between a wire bond pad 1219 and the underlying semiconductor material 1280. Similarly, a thick dielectric layer 1202 can be formed between wire bond pads 1217 and 1218 and the semiconductor material 1201 in the cut-out space 1281. As mentioned above, this structure results in a more uniform current distribution. This is more realistic to see in larger and/or higher current leds.

Referring to fig. 22B, the area of the cutout space 1201 is shown to be reduced relative to the cutout space of fig. 22A in a manner similar to fig. 21B. Furthermore, two thick dielectric layers 1204 and 1283 may be formed between wire bond pad 1219 and the underlying semiconductor material 1280. Similarly, a thick dielectric layer 1202 can be formed between wire bond pads 1217 and 1218 and the semiconductor material 1201 in the cut-out space 1281.

Referring to fig. 22C, the p-type wire extension 1203 extends under the n-type pad thick dielectric layer 1202 such that an end 1230 of the p-type wire extension is extended to the right side of the thick dielectric layer 1202. Furthermore, two thick dielectric layers 1204 and 1283 may be formed between wire bond pad 1219 and the underlying semiconductor material 1280. Similarly, a thick dielectric layer 1202 can be formed between wire bond pads 1217 and 1218 and the semiconductor material 1201 in the cut-out space 1281.

Referring to fig. 23A-23C, the positions of the p-type layer and the n-type layer can be interchanged (with the result that the positions of the wire bond pads, insulators, etc. are also interchanged), showing that the structures of fig. 22A-22C are suitable for use in any device. Thus, n-pad 1507 and thick n-pad dielectric 1503 are formed over the cut-out 1504, while p-bond pads 1511 and 1512 and thick p-bond pad dielectric 1501 are not formed over the cut-out 1504 (the reverse of the structure shown in fig. 22A-22C). Accordingly, the electrodes are reversed relative to those shown in fig. 22A-22C.

Referring to fig. 24, a two-electrode led is shown, which can promote more uniform current distribution. An n-type bond pad 2403 and a p-type bond pad 2404 are formed on a semiconductor material 2401. n-type bond pad 2403 has a thick dielectric layer 2406 formed between itself and semiconductor material 2401. Similarly, p-pad 2404 has a thick dielectric layer 2407 formed between itself and semiconductor material 2401.

A cut-out 2402 facilitates n-type bond pad 2403 to contact the n-type layer of the semiconductor 2401. A portion of n-type wire bond pads 2403 can be formed outside of cut out 2402 (and thus above the p-type layer of semiconductor material 2401) and a portion of n-type wire bond pads 2403 can be formed inside of cut out 2402 (providing the n-type layer electrical contact). Likewise, a portion of the thick dielectric layer 2406 can be formed outside of the moat 2402 (and thus above the p-type layer of the semiconductor material 2401) and a portion of the thick dielectric layer 2406 can be formed inside of the moat 2402.

n-type wire bond pad 2403 and thick dielectric layer 2406 thus extend down the n-type layer of semiconductor material 2401 to its p-type layer along one side of the cut out 2402, in a manner similar to that shown in fig. 21B. This configuration minimizes the size of the cut-out 2402, which, as discussed above, increases the brightness and efficiency of the led.

p-type wires or p-type extension wires 2407 extend from p-type bond pads 2404 so as to more evenly distribute current flowing through the active region of semiconductor 2401. A portion of p-type bond pad 2404 and all of extension wire 2407 can be formed directly over semiconductor material 2401 (without a thick dielectric layer therebetween).

Although fig. 15-24 only show a single thick dielectric layer, a series of one or more Distributed Bragg Reflector (DBR) pairs may be disposed between the thick dielectric layer and the electrode. Similarly, although fig. 15-24 show the electrode directly contacting the semiconductor material, the contact may be through an ohmic contact layer or a current distribution layer.

In accordance with one or more embodiments of the present invention, the thick dielectric layer may be non-perforated (non-perforated). That is, the cross-sectional structure of the dielectric layer is continuous and can be fabricated without any holes or perforations that would cause the cross-sectional structure of the thick dielectric layer to be discontinuous.

The dielectric material may be porous. Thus, the thick dielectric material may be too dense (having a high reflectance) to effectively reduce its density (and thus the reflectance) by making the dielectric material porous or discontinuous.

In view of the foregoing, one or more embodiments of the present invention provide a brighter and/or more efficient light emitting diode. Increasing the brightness of a light emitting diode increases its utility, making it more suitable for use in a wide range of applications. For example, brighter light emitting diodes are well suited for use in general lighting applications. Further, more efficient leds are desirable because they can be used to reduce costs (e.g., reduce the amount of power required to provide sufficient illumination).

The above-described embodiments do not limit the present invention. It should be understood that many modifications or variations are possible in light of the above teaching. The scope of the invention is defined by the claims.

Claims (32)

1. A semiconductor light emitting diode structure comprises a semiconductor and an electrode structure for providing a potential to the semiconductor, the electrode structure comprising:

a metal electrode; and

a light-transmissive dielectric material layer is formed on a semiconductor, the dielectric material having a refractive index greater than or equal to 1 and less than the refractive index of the semiconductor and a thickness greater than 1/2 of a wavelength λ of light in the dielectric material, the light being emitted by the semiconductor, the dielectric material being formed in a single layer corresponding to the metal electrode to increase total internal reflection of the light.

2. The led structure of claim 1, wherein the transparent dielectric layer is non-perforated and further comprises an ohmic contact layer contacting the metal electrode and the semiconductor and ohmically coupling the metal electrode to the semiconductor.

3. The electrode structure of the semiconductor light emitting diode according to claim 1, wherein:

a part of the metal electrode is electrically conducted with the semiconductor; and

another part of the metal electrode is arranged on the top surface of the dielectric material layer.

4. The structure of claim 1, wherein the dielectric material has a thickness of approximately 1.75 λ.

5. The light emitting diode structure of claim 1, wherein:

the metal electrode is formed on a semiconductor; and

the dielectric material layer is formed intermediate a portion of the metal electrode and the semiconductor.

6. The light emitting diode structure of claim 1, wherein:

the semiconductor comprises at least one material selected from the group consisting of:

aluminum gallium arsenide;

aluminum gallium indium phosphide;

aluminum gallium indium nitride; and

gallium arsenic phosphide.

7. The led structure of claim 1, wherein the dielectric material layer comprises at least one material selected from the group consisting of:

silicon dioxide;

silicon monoxide;

magnesium fluoride;

a siloxane polymer; and

air.

8. The led structure of claim 1, further comprising an ohmic contact layer formed between said metal electrode and said semiconductor.

9. The light emitting diode structure of claim 1, further comprising:

an ohmic contact layer formed between the metal electrode and the semiconductor; and wherein the ohmic contact layer comprises at least one material selected from the group consisting of:

indium tin oxide;

nickel oxide; and

rhodium dioxide.

10. The light emitting diode structure of claim 1, further comprising:

an ohmic contact layer formed between the metal electrode and the semiconductor; wherein the ohmic contact layer is a portion of the semiconductor; and wherein the ohmic contact layer comprises a heavily doped layer.

11. The led structure of claim 1, further comprising a current distribution layer formed between said metal electrode and said semiconductor.

12. The light emitting diode structure of claim 1, further comprising:

a current distribution layer formed between the metal electrode and the semiconductor; and wherein the current-distributing layer comprises at least one material selected from the group consisting of:

indium tin oxide;

nickel; and

rhodium dioxide.

13. The light emitting diode structure of claim 1, further comprising:

at least one pair of dielectric layers forms a distributed Bragg reflector structure and is arranged between the metal electrode and the dielectric material layer, wherein each pair of dielectric layers of the distributed Bragg reflector is substantially transparent and consists of a plurality of material layers with different refractive indexes, and the thickness of each pair of dielectric layers is approximate to a plurality of times of lambda/4.

14. The light emitting diode structure of claim 1,

wherein each of the DBR dielectric layers comprises at least one material selected from the group consisting of:

titanium dioxide;

titanium pentoxide;

titanium sesquioxide;

titanium oxide;

zirconium dioxide;

TiO₂ZrO₂Nb₂O₅；

cerium oxide;

zinc sulfide;

aluminum oxide;

silicon nitride;

indium tin oxide;

niobium pentoxide;

tantalum pentoxide;

a siloxane polymer; silicon oxide; silicon dioxide, or magnesium fluoride.

15. The led structure of claim 1, wherein the metal electrode comprises at least one metal layer.

16. The light emitting diode structure of claim 15,

wherein the metal layer is selected from the group:

aluminum;

silver;

(ii) rhodium;

lead;

copper;

gold;

chromium;

platinum;

titanium;

a nickel/gold alloy;

chromium/gold alloys;

a silver/aluminum mixture; and combinations thereof.

17. The led structure of claim 1, wherein the led defines a lateral structure having both the metal electrode and a second metal electrode formed on a single side of the semiconductor.

18. The led structure of claim 1, wherein the led defines a vertical structure having both the metal electrode and a second metal electrode formed on an opposite side of the semiconductor.

19. The led structure of claim 1, wherein a portion of the metal electrode forms a wire bonding area.

20. The led structure of claim 1, wherein a portion of the metal electrode electrically contacts the semiconductor along an edge of the dielectric material layer.

21. The led structure of claim 1, wherein a portion of the metal electrode electrically contacts the semiconductor through an opening in the dielectric material layer.

22. The light emitting diode structure of claim 1, wherein the dielectric material is porous.

23. The led structure of claim 1, wherein the dielectric material comprises porous indium tin oxide.

24. The led structure of claim 1, wherein the dielectric material is porous silica.

25. The led structure of claim 1, wherein the porosity of the dielectric material is sufficient to reduce the effective refractive index of the dielectric material such that total reflection occurs within the semiconductor.

26. A light emitting diode comprising an aluminum gallium indium nitride material configured to emit light having a center wavelength of about λ and a reflective electrode structure, the reflective electrode structure comprising:

a metal electrode;

a silicon dioxide dielectric material layer is formed on the aluminum gallium indium nitride material in a single layer, and the thickness of the dielectric material layer is more than or equal to lambda/2; and

wherein at least a portion of the metal electrode is formed over the silicon dioxide dielectric material layer, and another portion of the metal electrode is in ohmic contact with the aluminum gallium indium nitride material.

27. The light-emitting diode of claim 26, wherein the silicon dioxide dielectric material layer and the metal electrode are in physical contact with the aluminum gallium indium nitride material through an indium tin oxide layer.

28. A reflective electrode structure for a gallium nitride material configured to emit light having a center wavelength of about λ, comprising:

a metal electrode;

a layer of silicon dioxide dielectric material is formed as a single layer on the gallium nitride material, the layer of silicon dioxide dielectric material having a thickness of approximately 1.75 λ;

at least one pair of distributed Bragg reflectors is formed on the silicon dioxide material; and wherein a portion of the metal electrode is formed over the silicon dioxide dielectric material layer and the pair of distributed Bragg reflectors, and another portion of the metal electrode is in ohmic contact with the gallium nitride material.

29. The reflective electrode structure of claim 28, wherein each layer of the dbr pair is transparent to light, each layer has a different refractive index, and the thickness of each dbr pair is approximately a multiple of λ/4.

30. The reflective electrode structure of claim 28, wherein the silicon dioxide dielectric material and the metal electrode are in physical contact with the gallium nitride material through an indium tin oxide layer.

31. A method of forming an electrode structure for a light emitting diode, the method comprising forming a layer of dielectric material having a thickness greater than 1/2 a wavelength λ of light in the dielectric material as a single layer on a semiconductor material, and forming a conductive electrode such that the dielectric material isolates at least a portion of the conductive electrode from the semiconductor material and such that another portion of the conductive electrode electrically contacts the semiconductor material.

32. An electrode structure for a light emitting diode, the light emitting diode comprising a semiconductor material having an n-type portion and a p-type portion, the electrode structure comprising:

a metal n-type electrode electrically connected to the n-type portion of the semiconductor material;

a metal p-type electrode electrically connected to the p-type portion of the semiconductor material;

a layer of light-transmissive dielectric material formed in a single layer relative to at least one of the n-type electrode and the p-type electrode to enhance total internal reflection of light, the layer of dielectric material having a thickness of approximately 1.75 times a wavelength λ of light in the dielectric material; and wherein the semiconductor material, the n-type electrode and the p-type electrode cooperate to define a lateral light emitting diode structure.