KR100576847B1 - Gallium nitride based semiconductor light emitting device and manufacturing method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride-based semiconductor light emitting device, comprising: a substrate for growing a gallium nitride-based semiconductor material, a lower clad layer formed on the substrate and including a first conductivity type GaN-based semiconductor material; An active layer including an undoped GaN semiconductor material, an upper clad layer formed on the active layer and including a second conductivity type GaN semiconductor material, and formed on the upper clad layer; Provided is a gallium nitride based semiconductor light emitting device comprising a metal layer made of one metal selected from the group consisting of Ni, Ti, Pt, Au, Mg, Se, Pd, and W, and an ITO layer formed on the metal layer.

According to the present invention, the transmittance can be improved compared to the conventional transparent electrode made of Ni / Au, and the contact resistance can be reduced by forming an ohmic contact as well as bonding the ITO film and the GaN layer more firmly. As a result, it is possible to provide a light emitting device having improved luminance at the same driving voltage.

Transparent electrode, indium tin oxide (ITO), ohmic contact

Description

GALLIUM NITRIDE BASED SEMICONDUCTOR LIGHT EMITTING DIODE AND METHOD OF PRODUCING THE SAME}

1 is a cross-sectional view showing the structure of a conventional gallium nitride-based semiconductor light emitting device.

2 is a cross-sectional view showing the structure of a gallium nitride semiconductor light emitting device according to an embodiment of the present invention.

3A and 3B are plan views of a light emitting device having a mesh metal layer according to another embodiment of the present invention.

4A to 4E are process perspective views for explaining a method of manufacturing a gallium nitride based semiconductor light emitting device according to the present invention.

<Code Description of Main Parts of Drawing>

31,111: Sapphire substrate 33,113: First conductivity type GaN cladding layer

34, 114: active layer 35, 115: second conductivity type GaN cladding layer

116: photoresist 37,117: barrier metal layer

38, 118: ITO layer 41, 121: first bonding electrode

42,112: second bonding electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride based semiconductor light emitting device, and more particularly, to a semiconductor light emitting device capable of obtaining high brightness characteristics at the same driving voltage by reducing contact resistance and improving light transmittance in the vicinity of an electrode, and a method of manufacturing the same. It is about.

In recent years, full-color implementations have been possible by developing light emitting devices capable of emitting blue, green, and ultraviolet light using gallium nitride (GaN) -based compound semiconductors.

Since such a gallium nitride compound semiconductor can be grown on a sapphire substrate which is generally an insulating substrate, electrodes cannot be provided on the back of the substrate as in GaAs-based light emitting devices, and both electrodes must be formed on the crystal-grown semiconductor layer side. . The structure of such a conventional GaN-based light emitting device is illustrated in FIG.

Referring to FIG. 1, a GaN light emitting device 20 includes a first conductive cladding layer 13, an active layer 14, and a second conductive type sequentially formed on a sapphire growth substrate 11 and the sapphire substrate 11. The cladding layer 15 is included.

The first conductive cladding layer 13 may be formed of an n-type GaN layer 13a and an n-type AlGaN layer 13b, and the active layer 14 may be undoped with a multi-quantum well structure. It may be made of an InGaN layer. In addition, the second conductivity-type cladding layer 15 may be composed of a p-type GaN layer 15a and a p-type AlGaN layer 15b. In general, the semiconductor crystal layers 13, 14, and 15 may be grown using a process such as MOCVD. At this time, in order to improve lattice matching with the sapphire substrate 11 before growing the n-type GaN layer 13a, a buffer layer such as AlN / GaN (not shown) may be formed in advance.

As described above, since the sapphire substrate 11 is an electrically insulating material, in order to form both electrodes on the upper surface, the n-type p-type cladding layer 15 and the active layer 14 corresponding to a predetermined region are etched. A part of the top surface of the clad layer 13 (specifically, the n-type GaN layer 13a) is exposed, and the first electrode 21 is formed on the exposed top surface of the n-type GaN 13a.

On the other hand, since the p-type GaN layer 15a has a relatively high resistance, an additional layer capable of forming an ohmic contact with a conventional electrode is required. To this end, U.S. Patent No. 5,563,422 (Applicant: Nichia, Japan, published on October 8, 1996), before forming the second electrode 22 in the p-type GaN layer 15a, Ni / to form an ohmic contact A method of forming a transparent electrode composed of Au is proposed. The transparent electrode 18 has an effect of lowering the forward voltage V _f by forming an ohmic contact while increasing the current injection area.

However, the transmittance of the transparent electrode 18 composed of Ni / Au is only about 60%, which is relatively low. Such low transmittance lowers the overall luminous efficiency when the light emitting device is packaged by wire bonding.

In order to overcome the low transmittance problem, a method of forming an indium tin oxide (ITO) layer known to have a transmittance of about 90% or more in place of the Ni / Au layer has been proposed. However, ITO has a weak adhesion to GaN crystals, and the work function of p-type GaN is 7.5 eV, whereas the work function of ITO is 4.7-5.2 eV, so when ITO is deposited directly on the p-type GaN layer, ohmic contact It is not formed. Therefore, in order to alleviate the difference in work function to form an ohmic contact, a conventional thin Zn or C doped Ni / Au layer had to be additionally formed.

However, Zn or C of the Ni / Au layer has high mobility and can diffuse into the p-type GaN layer when used for a long period of time, thereby lowering the reliability of the device. In addition, in order to obtain a desired ohmic contact, not only the formation of the layer, but also the growth temperature and speed at the time of p-type GaN crystal growth have a burden of appropriate control.

As a result, even if ITO is used, only the transmittance is improved, and in order to form an ohmic contact, it is necessary to take a bad influence on device reliability due to diffusion of Zn or the like, and the GaN crystal growth process has been complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above technical problem, and an object thereof is to provide a gallium nitride-based semiconductor light emitting device which improves the problem of contact resistance with a p-type GaN layer while using an ITO film having a high transmittance as a transparent electrode.

Another object of the present invention is to provide a method for manufacturing the semiconductor light emitting device.

In order to achieve the above technical problem, the present invention,

A substrate for growing a gallium nitride-based semiconductor material, a lower clad layer formed on the substrate and including a first conductive GaN-based semiconductor material, and a portion of the lower conductive clad layer, and undoped GaN An active layer including a semiconductor material, an upper cladding layer formed on the active layer and including a second conductivity type GaN-based semiconductor material, and formed on the upper cladding layer, and including Ni, Ti, Pt, Au, Mg, Se, A gallium nitride based semiconductor light emitting device comprising a metal layer made of one metal selected from the group consisting of Pd and W, and an ITO layer formed on the metal layer.

The thickness of the metal layer is preferably about 100 kPa or less. In addition, to improve the transmittance, the metal layer and the ITO layer may be formed in a mesh shape, preferably, the total area of the metal layer and the ITO layer is formed to occupy at least 5% of the upper surface of the upper clad layer. do.

Furthermore, the present invention provides a method of manufacturing a gallium nitride-based semiconductor light emitting device. The method includes providing a substrate for growing a gallium nitride based semiconductor material, forming a lower clad layer with a first conductivity type GaN based semiconductor material on the substrate, and forming a lower clad layer on the lower conductive clad layer. Forming an active layer from an undoped GaN-based semiconductor material, forming an upper cladding layer of a second conductivity type GaN-based semiconductor material on the active layer, and removing the partial region of the at least the upper cladding layer and the active layer Exposing a portion of the lower clad layer, forming a metal layer on the upper clad layer from a metal selected from the group consisting of Ni, Ti, Pt, Au, Mg, Se, Pd, and W; Forming an ITO layer.

In a preferred embodiment, the forming of the metal layer and the forming of the ITO layer may be the step of forming the metal layer and the ITO layer in a mesh shape, respectively.

At this time, the total area of the metal layer and the ITO layer is preferably formed to occupy at least 5% of the upper surface of the upper clad layer.

In an embodiment for forming a mesh-shaped metal layer and an ITO layer, forming the metal layer includes forming a photoresist on an upper surface of the upper clad layer and an exposed upper surface of the lower clad layer, and the upper cladding. The photoresist formed on the layer may be patterned into an inverse mesh shape, and the metal layer may be formed on the upper clad layer using the photoresist. In this embodiment, the step of forming the ITO layer is also formed using the photoresist to form the same mesh-shaped ITO layer on the metal layer, and after forming the ITO layer, it is preferable to remove the photoresist. Do.

In addition, it is preferable that the metal layer and / or the ITO layer be grown by an E-beam evaporator.

Furthermore, in order to improve the properties of the ITO layer, the method may further include heat treating the ITO layer. The heat treatment step of the ITO layer is preferably carried out for at least 30 seconds at a temperature of about 200 ℃ or more in a nitrogen atmosphere.

Hereinafter, with reference to the accompanying drawings will be described the present invention in more detail.

2 is a cross-sectional view showing a structure of a gallium nitride based semiconductor light emitting device according to an embodiment of the present invention.

Referring to FIG. 2, the GaN light emitting device 40 includes a sapphire substrate 31 for growing a gallium nitride based semiconductor material, a first conductive cladding layer 33, and an active layer sequentially formed on the sapphire substrate 31. 34) and the second conductive cladding layer 35.

The first conductive cladding layer 33 may be formed of an n-type GaN layer 33a and an n-type AlGaN layer 33b, and the active layer 34 may be undoped with a multi-quantum well structure. It may be made of an InGaN layer. In addition, the second conductivity type cladding layer 35 may be composed of a p-type GaN layer 35a and a p-type AlGaN layer 35b. In general, the semiconductor crystal layers 33, 34 and 35 may be grown using a process such as MOCVD. At this time, in order to improve lattice matching with the sapphire substrate 31 before growing the n-type GaN layer 33a, a buffer layer such as AlN / GaN (not shown) may be formed in advance.

A portion of the upper surface of the first conductive clad layer 35 is exposed to a region where the second conductive clad layer 35 and the active layer 34 corresponding to a predetermined region are removed. The first electrode 41 is disposed on the exposed top surface of the first conductive cladding layer 33 (which is an n-type GaN layer 33a in FIG. 2).

In addition, the second electrode 42 is formed on an ITO layer (Indium Titanium Oxide layer) 38. Since the p-type GaN layer 35a has a relatively high resistance and a large work function (about 7.5 eV) compared to the n-type GaN layer 33a, the barrier metal layer (I) may be used to form an ohmic contact with the ITO layer 38. 37) is further formed. The barrier metal layer 37 employed in the present invention is composed of one metal selected from the group consisting of Ni, Ti, Pt, Au, Mg, Se, Pd and W.

The barrier metal layer 37 is an intermediate layer for solving the problem in employing the ITO layer 38 having excellent transmittance. That is, the metal layer 37 made of the material not only improves the adhesion between the ITO layer 38 and the GaN layer 35a, but also intermediate the work function of the p-type GaN layer 35a and the ITO layer 38. Since it is formed of a metal having a phosphorus work function, the contact resistance can be reduced.

Accordingly, the ITO layer 38 and the metal layer 37 may be formed firmly, and the forward voltage V _f may be lowered by forming an ohmic contact while increasing the current injection efficiency.

In addition, since the metal layer 37 has a lower transmittance relative to the ITO layer 38, in order to further improve the overall transmittance, the thickness is preferably about 100 GPa or less, more preferably about 50 GPa. Form.

The semiconductor light emitting device according to the present invention can be implemented to be suitable for the wire bonding method in which the semiconductor crystal growth surface is the main light emitting direction. In this manner, in order to further improve the luminous efficiency toward the semiconductor crystal growth surface side, it is preferable to employ the metal layer and the ITO layer in a mesh shape for further improving the transmittance. The mesh type metal layer and the ITO layer that can be employed in the present invention will be described by way of example with the light emitting device shown in Figs. 3A and 3B.

Fig. 3A is a top plan view of a light emitting device including a metal layer and an ITO layer 68 in a mesh form having rectangular holes h as a preferred embodiment of the present invention.

Referring to Fig. 3A, there is shown a light emitting device having a p-type GaN cladding layer 65 and a portion of the n-type GaN cladding layer 63 removed.

A first electrode 71 is disposed on the n-type cladding layer 63, and a metal layer (not shown) and an ITO layer 68 having the same mesh shape are sequentially disposed on the p-type cladding layer 65, The second electrode 72 is disposed in a predetermined region of the ITO layer 68.

The metal layer and the ITO layer 68 may have a net-like shape in the upper surface region of the p-type cladding layer 65, and may be formed in the p-type GaN cladding layer 65 through a plurality of regularly arranged rectangular holes h. Some may be exposed. Accordingly, the metal layer and the ITO layer 68 maintain the actual current injection area at the same level as the conventional one, while directly emitting light generated from the active layer (not shown) through the regions exposed through the regularly arranged holes. The luminous efficiency can be improved.

As such, the mesh type metal layer and the ITO layer for improving the luminous efficiency by exposing a part of the p-type cladding layer while maintaining the current injection efficiency may be implemented in various forms.

FIG. 3B is a top plan view of a light emitting device including another ITO layer 88 and another mesh-like metal layer composed of a plurality of circular portions 88a connected to each other in FIG. 3A.

Referring to FIG. 3B, a first electrode 91 is disposed on the exposed n-type cladding layer 83, and a metal layer (not shown) and an ITO layer 88 having the same mesh shape on the p-type cladding layer 85. ) Are sequentially arranged, and the second electrode 92 is disposed in a predetermined region of the ITO layer 88.

The metal layer and the ITO layer 88 basically have a net-like shape as shown in FIG. 3A, but have a shape formed by a circularly arranged circular portion 88a and a portion 88b connecting thereto. The metal layer and the ITO layer 88 having such a shape also maintain a substantial current injection area at the same level as conventionally, and simultaneously emit light generated from an active layer (not shown) directly through the exposed p-type cladding layer region. The efficiency can be improved.

In order to maintain the current injection efficiency as in the prior art, the mesh-type metal layer and the ITO layer 68, which are entirely meshed on the upper surface of the p-type cladding layer 65, are formed to occupy at least 5% of the surface area of the upper surface. It is desirable to.

In the embodiment shown in Figs. 3A and 3B, it is preferable to form the total area of the mesh metal layer and the ITO layers 68 and 88 in a predetermined area or more in order to maintain the current injection efficiency as in the prior art. That is, the mesh type metal layer and the ITO layers 68 and 88, which are entirely meshed on the upper surfaces of the p-type cladding layers 65 and 85, are preferably formed to occupy at least 5% of the surface area of the upper surface.

4A to 4E are process perspective views for explaining a method of manufacturing a gallium nitride based semiconductor light emitting device according to the present invention.

First, as shown in FIG. 4A, the first conductivity type GaN cladding layer 113, the active layer 114, and the second conductivity type GaN cladding layer 115 are sequentially formed on the substrate 111 for growing a gallium nitride semiconductor material. To form. The growth substrate 111 may be a sapphire substrate, and the first conductive cladding layer 113 and the second conductive cladding layer 115 may each have a GaN layer and an AlGaN layer as shown in FIG. 2. It may be formed by, and may be formed by the MOCVD process.

Next, as shown in FIG. 4B, at least a portion of the second conductivity-type cladding layer 115 and the active layer 114 are removed to expose the partial region 113a of the lower cladding layer 113. The exposed region 113a of the lower clad layer 113 is provided as a region where the electrode is to be formed. The shape of the structure according to the present removal process may be changed in various forms according to the position to form the electrode, and the shape and size of the electrode may also be variously modified. For example, the present process may be implemented by removing an area in contact with one edge, and in order to disperse current density, the shape of the electrode may be formed to extend along the side.

Next, a process of forming the barrier metal layer and the ITO layer is performed. This embodiment is a process for forming the metal layer and the ITO layer of the shape shown in Fig. 3B, which is illustrated in Figs. 4C and 4D.

As shown in FIG. 4C, a photoresist 116 is formed on an upper surface of the second conductive cladding layer 115 and an exposed upper surface 113a of the first conductive cladding layer 13. The photoresist 116 formed on the clad layer 115 is patterned onto an inverse mesh, which is the inverse of the desired mesh shape. The shape of the metal layer and the ITO layer that can be employed in the present invention is distributed over the entire area so as to be interconnected like a mesh, thereby uniformly forming a current distribution, while part of the second conductive cladding layer 115 is formed through the voids. It is a mesh shape that can be exposed. In this process, the photoresist 116 is formed to have a thickness greater than at least the thickness of the metal layer and the ITO layer to be formed.

Subsequently, as shown in FIG. 4D, the metal layer 117 and the ITO layer 118 of the mesh shape are sequentially deposited on the second conductive cladding layer 115 using the photoresist (116 of FIG. 4C). The photoresist 116 is removed through a lift-off process. Thus, the metal layer 117 and the ITO layer 118 having the desired mesh phase can be obtained through the photoresist 116 patterned in the reverse mesh phase. In the present invention, the barrier metal layer 117 deposited on the second conductive cladding layer 115 is a group consisting of Ni, Ti, Pt, Au, Mg, Se, Pd, and W for improving transmittance and forming ohmic contact. It is deposited with one metal selected from. The deposition process of the metal layer 117 and / or ITO layer 118 is preferably carried out by an electron beam evaporator (E-beam evaporator) in order to prevent an increase in contact resistance by hydrogen ions.

Finally, as shown in FIG. 4E, first and second electrodes 121 and 122 are formed in the exposed region of the ITO layer 118 and the first conductive clad layer 117 as a bonding metal. Prior to the electrode process of FIG. 4E, the step of heat-treating the ITO layer may be additionally performed to always maintain characteristics such as transmittance. The heat treatment of the ITO layer is preferably performed at a temperature of about 200 ° C. or more for at least 30 seconds in a nitrogen atmosphere.

4A and 4E correspond to specific embodiments of the present invention, and the present invention is not limited thereto. That is, the process of forming the metal layer and the ITO layer on the mesh illustrated in FIGS. 4C and 4D may be selectively employed. For example, the barrier metal layer may be formed on the entire second conductive type cladding layer at a thickness (about 100 GPa) that may have an appropriate transmittance, and in this case, the barrier metal layer may be higher than the transmittance (about 60%) of the conventional Ni / Au layer. Transmittance (about 70% or more).

Also, in the case of forming the metal layer and the ITO layer on the mesh, unlike in FIGS. 4C and 4D, after forming the metal layer and the ITO layer in the entire area of the second conductive cladding layer, a photoresist patterned into a desired mesh is realized. By etching to obtain a metal layer and an ITO layer of the same shape.

As such, the present invention is not limited by the above-described embodiments and the accompanying drawings, and is intended to be limited by the appended claims, and various forms of substitution may be made without departing from the technical spirit of the present invention described in the claims. It will be apparent to one of ordinary skill in the art that modifications, variations and variations are possible.

As described above, according to the present invention, before forming the ITO film having a high transmittance as a transparent electrode, the barrier metal layer made of one metal selected from the group consisting of Ni, Ti, Pt, Au, Mg, Se, Pd and W is p; By forming on the type GaN layer in advance, it is possible to strengthen the adhesive force and form a desired ohmic contact. In addition, by implementing the metal layer and the ITO film in a mesh form, it is possible to significantly improve the transmittance while maintaining excellent current injection efficiency.

Claims (14)

A substrate for growing a gallium nitride based semiconductor material; A lower clad layer formed on the substrate and including a first conductivity type GaN semiconductor material; An active layer formed on a portion of the lower conductive clad layer and including an undoped GaN-based semiconductor material; An upper clad layer formed on the active layer and including a second conductivity type GaN semiconductor material; A p-side electrode formed on the upper clad layer and comprising a metal layer made of one metal selected from the group consisting of Ni, Ti, Pt, Au, Mg, Se, Pd, and W, and an ITO layer formed on the metal layer; And said p-side electrode structure has a mesh shape. The method of claim 1, The metal layer has a gallium nitride-based semiconductor light emitting device, characterized in that having a thickness of less than 100Å. delete The method of claim 1, And a total formation area of the metal layer and the ITO layer is 5% or more of the upper surface of the upper clad layer. Providing a substrate for growing a gallium nitride based semiconductor material; Forming a lower clad layer of a first conductivity type GaN semiconductor material on the substrate; Forming an active layer of an undoped GaN-based semiconductor material on the lower conductive clad layer; Forming an upper clad layer of a second conductivity type GaN semiconductor material on the active layer; Exposing a portion of the lower clad layer by removing a portion of the at least upper clad layer and the active layer; Forming a metal layer on the upper clad layer with one metal selected from the group consisting of Ni, Ti, Pt, Au, Mg, Se, Pd and W; Forming the ITO layer on the metal layer; And A method of manufacturing a gallium nitride-based semiconductor light emitting device, comprising: patterning the metal layer and the ITO layer in a mesh shape. The method of claim 5, The metal layer has a thickness of less than 100 GPa manufacturing method of a gallium nitride-based semiconductor light emitting device. delete The method of claim 5, The total formation area of the metal layer and the ITO layer is at least 5% of the upper surface of the upper clad layer manufacturing method of the gallium nitride-based semiconductor light emitting device. The method of claim 5, Patterning the metal layer and the ITO layer, Forming the photoresist; Patterning the inverse mesh shape; And etching the exposed portions of the metal layer and the ITO layer using the photoresist. delete The method of claim 5, Forming the metal layer, A method of manufacturing a gallium nitride-based semiconductor light emitting device, characterized in that for growing the ITO layer on the upper cladding layer by an E-beam evaporator. The method of claim 5, Forming the ITO layer, And growing an ITO layer on the metal layer by an electron beam evaporation method. The method of claim 5, The method of manufacturing a gallium nitride-based semiconductor light emitting device further comprising the step of heat-treating the ITO layer. The method of claim 13, The heat treatment of the ITO layer, A method of manufacturing a gallium nitride-based semiconductor light emitting device, characterized in that the step of heat-treating the ITO layer for 30 seconds or more at a temperature of 200 ℃ or more in a nitrogen atmosphere.

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