HK1144614A - Light-emitting diode chip with high extraction and method for manufacturing the same - Google Patents

Description

Light-emitting diode chip with high light extraction and method for the production thereof

Prior Art

Priority of taiwan patent application No.96135296, filed on 21/9/2007, is hereby incorporated by reference in its entirety as if fully set forth herein.

Technical Field

The present invention relates to a chip, and more particularly, to a light emitting diode chip having high light extraction efficiency.

Background

Referring to fig. 1, a conventional led chip 1 is shown. Fig. 1 includes a substrate 11, an epitaxial layer structure 12 on the substrate 11, and an electrode unit 13 composed of an N-type electrode 131 and a P-type electrode 132.

As one example, the epitaxial-layer structure 12 is formed of a GaN-based material, and has a first N-type cladding layer 121, an active layer 122 formed on the first cladding layer 121, and a second P-type cladding layer 123. The first cladding layer 121 and the second cladding layer 123 are opposite to each other, and form a carrier injector with respect to the active layer 122. Thus, when power is supplied to the epitaxial-layer structure 12, electrons and holes recombine in the active layer 122, and then release energy in the form of light.

For example, the N-type electrode 131 and the P-type electrode 132 are composed of Au, Ni, Pt, Ag, Al, etc. and/or alloys thereof. The N-type electrode 131 is disposed on the first cladding layer 121 of the epitaxial-layer structure 12 and forms an ohmic contact with the first cladding layer 121 of the epitaxial-layer structure 12. The P-type electrode 132 is disposed on the second cladding layer 123 and forms an ohmic contact with the second cladding layer 123 such that the N-type electrode 131 and the P-type electrode 132 supply power to the epitaxial layer structure 12.

When electric energy is supplied to the N-type electrode 131 and the P-type electrode 132, current diffuses and flows through the epitaxial layer structure 12, and electrons and holes are injected into the active layer 122, and the electrons and holes recombine with each other and then release energy in the form of light.

The refractive index of the GaN-based material is about 2.6 and the refractive index of its surrounding material (typically air) is 1, or surrounded by a transparent encapsulation material for packaging and having a refractive index of 1.4. The top surface 124 of the second cladding layer 123 of the epitaxial-layer structure 12 of the light-emitting diode chip 1 is planar. Due to their direction of propagation, some of the light generated from epitaxial layer structure 12 will follow Snell's law and will not escape epitaxial layer structure 12. Therefore, the light extraction of the light emitting diode chip 1 is not good.

Referring to fig. 2, there are numerous documents and patents that propose roughening the top surface 124 'of the led chip 1' such that light impinging on the roughened top surface 124 'has various possible angles of incidence with respect to the roughened top surface 124'. Therefore, the probability of light escaping the epitaxial-layer structure 12' is increased, and the light extraction efficiency is improved.

However, light generated from the epitaxial-layer structure 12 'does not propagate entirely toward the top surface 124'. Light propagating towards the substrate 11 'faces a similar situation as at the top surface and cannot escape the epitaxial layers 12' to enter the surrounding environment. Therefore, the light extraction is still low.

Some document proposes forming a mirror layer connected to the epitaxial layer structure 12' capable of reflecting light. It is desirable that light propagating toward the substrate 11 ' may be reflected toward the top surface 124 ' to increase the likelihood that light generated from the epitaxial layer structure 12 ' escapes the epitaxial structure and enters the ambient environment. However, light propagating towards the substrate 11 ' will be confined in the epitaxial-layer structure 12 ' due to its propagation direction and cause total internal reflection inside the epitaxial-layer structure 12 '. Also, the active layer may absorb light. The mirror layer on the substrate 11' substantially does not improve the light extraction of the led chip.

It is intended to improve the structure of the light emitting diode 1, 1' to increase light extraction and brightness.

Disclosure of Invention

The light emitting diode chip includes a substrate, a transparent refractive layer having a predetermined thickness and having a refractive index greater than that of air and less than that of an epitaxial layer structure, and an electrode unit.

The electrons and holes recombine and release energy in the form of light. The epitaxial layer structure has a bottom surface connected to the transparent refractive layer and a top surface opposite to the bottom surface. The bottom surface and the top surface are roughened to have a roughness of not less than 100nm root mean square (rms).

The electrode unit has a pair of electrodes that are separately disposed on the epitaxial layer structure and form ohmic contacts with the epitaxial layer structure to supply current to the electrodes.

A method for manufacturing a light emitting diode chip with high light extraction (high light extraction) of the present invention includes the steps of: the method includes the steps of forming an epitaxial layer structure, performing a first roughening step, forming a pair of electrodes, forming a temporary substrate, performing a second roughening step, forming a substrate, and removing the temporary substrate.

The step of forming the epitaxial layer structure includes: a GaN-based epitaxial layer structure having a first N-type clad layer, an active layer, and a second P-type clad layer is formed on a substrate.

The first roughening step is to roughen a top surface of the second cladding layer of the epitaxial-layer structure to have a roughness of not less than 100nm rms.

The step of forming the pair of electrodes includes separately forming a pair of electrodes on the first clad layer and the roughened top surface of the second clad layer, respectively, and forming ohmic contacts therewith.

The step of forming the temporary substrate is to separately form the temporary substrate on the second cladding layer and remove the substrate under the epitaxial-layer structure to expose the bottom surface of the first cladding layer.

The second roughening step is to roughen the bottom surface of the first clad layer to have a roughness of not less than 100 nmrms.

The step of forming the substrate is attaching the substrate to the bottom surface of the first cladding layer with glue having a predetermined refractive index and being transparent to light generated from the epitaxial-layer structure.

When the step of removing the temporary substrate is completed, the fabrication of the light emitting diode chip having high light extraction efficiency is completed.

Another method for manufacturing a light emitting diode chip having high light extraction efficiency includes the steps of: the method includes the steps of forming an epitaxial layer structure, performing a first roughening step, forming a pair of electrodes, forming a temporary substrate, performing a second roughening step, forming a transparent refractive layer, forming a substrate, and removing the temporary substrate.

The step of forming the epitaxial layer structure includes: a GaN-based epitaxial layer structure having a first N-type clad layer, an active layer, and a second P-type clad layer is formed on a substrate.

The first roughening step is to roughen a top surface of the second cladding layer of the epitaxial-layer structure to have a roughness of not less than 100 nm.

The step of forming the pair of electrodes includes separately forming a pair of electrodes on the first clad layer and the roughened top surface of the second clad layer, respectively, and forming ohmic contacts therewith.

The step of forming the temporary substrate is to separately form the temporary substrate on the second cladding layer and remove the substrate under the epitaxial-layer structure to expose the bottom surface of the first cladding layer.

The second roughening step is to roughen the bottom surface of the first clad layer to have a roughness of not less than 100 nmrms.

The step of forming the transparent refractive layer is to form a transparent refractive layer having a refractive index greater than that of air and less than that of the epitaxial-layer structure, and having a thickness of not more than 5 μm, the transparent refractive layer being connected to the first cladding layer of the epitaxial-layer structure.

The step of forming the substrate is to form a substrate having a high thermal conductivity coefficient connected to the transparent refractive layer.

The step of removing the temporary substrate produces a light emitting diode chip with high light extraction efficiency.

The present invention provides a manufacturing process for producing a light emitting diode chip having an epitaxial layer structure including a top surface and a bottom surface having a predetermined roughness. Light generated from the epitaxial layer structure can be efficiently extracted from the diode chip through the roughened top and bottom surfaces of the epitaxial layer structure. In addition, the transparent refractive layer forms an interface between the epitaxial layer structure and the substrate, and can effectively reflect light traveling toward the substrate back toward the top surface of the diode chip to improve light extraction efficiency.

Drawings

Fig. 1 is a schematic cross-sectional view of a conventional light emitting diode chip;

fig. 2 is a schematic cross-sectional view of another conventional light emitting diode chip;

fig. 3 is a schematic cross-sectional view of a light-emitting diode chip according to a first aspect of the invention;

fig. 4 is a process flow for manufacturing the light emitting diode chip of the first aspect of the present invention;

FIGS. 5-10 are schematic cross-sectional views corresponding to stages of the process flow of FIG. 4;

fig. 11 is a schematic cross-sectional view of a light-emitting diode chip according to a second aspect of the invention;

fig. 12 is a process flow of the light emitting diode chip of the second aspect of the present invention; and

fig. 13 is a schematic cross-sectional view of a light-emitting diode chip according to a third aspect of the present invention.

Detailed Description

The light emitting diode chip with high light extraction efficiency provided by the present invention will be described and explained in detail by the following aspects in conjunction with the accompanying drawings. It should be noted that in the following description, like elements are denoted by like reference numerals.

Referring to fig. 3, a cross-sectional view of a light emitting diode chip according to a first aspect of the invention is shown. The light emitting diode chip includes a substrate 21, a transparent refractive layer 22, an epitaxial layer structure 23, and an electrode unit 24.

The substrate 21 includes a base substrate 211 and a mirror layer 212. The mirror layer is connected to the base substrate 211 and on the base substrate 211. The base substrate 211 is made of a material including silicon, high thermal conductive ceramic, or high thermal conductive metallic material. The base substrate 211 serves to support the transparent refractive layer 22 and the epitaxial layer structure 23, etc. The mirror layer 212 may be formed of Al, Ag, Au, Pt, Pd, Rb, or a combination thereof. The mirror layer 212 may also be formed of high refractive index dielectric layers and low refractive index dielectric layers alternately arranged with each other. The mirror layer 212 serves to reflect light generated from the outer pressure layer structure 23 traveling toward the substrate 21.

The transparent refractive layer 22 has a thickness of not more than 5 μm and is a glue formed of a polymer or a dielectric material, wherein the polymer has a high thermal conductivity of up to 0.2W/m.k or more and has a refractive index between 1 and 2. The transparent refractive layer 22 serves to reflect light traveling toward the substrate 21, thereby improving light extraction.

The epitaxial layer structure 23 is formed of a GaN-based material, and includes a first N-type clad layer 231, an active layer 232 connected to the first N-type clad layer 231, and a second P-type clad layer 233 connected to the active layer 232 and opposite to the first N-type clad layer 231. The first cladding layer 231 and the second cladding layer 233 form a carrier injector with respect to the active layer 232 so that electrons and holes can recombine and release energy in the form of light emission. The bottom surface 235 of the epitaxial-layer structure 23 (i.e., the bottom surface of the first cladding layer 231) and the top surface 234 of the epitaxial-layer structure 23 (i.e., the top surface of the second cladding layer 233) are roughened by epitaxial growth, or wet etching, or inductively coupled plasma etching or photo-assisted chemical etching to become a non-continuous roughened surface having a roughness of not less than 100nm root mean square (rms). Root mean square means the average between the height deviation and the mean line/surface taken over the evaluation length/area. The epitaxial layer structure 23 is attached to the substrate 21 by a transparent refractive layer 22 (as glue between the epitaxial layer structure 23 and the substrate 21).

The electrode unit 24 includes N-type electrodes 241 and P-type electrodes 242 formed of, for example, Au, Ni, Pt, Ag, Al, or the like, or an alloy thereof. The N-type electrode 241 is disposed on the first cladding layer 231 and in ohmic contact with the first cladding layer 231. The P-type electrode 242 is disposed on the second cladding layer 233 and in ohmic contact with the second cladding layer 233. The N-type electrode 241 and the P-type electrode 242 supply electric power to the epitaxial-layer structure 23 and generate light.

When electrical energy is supplied to the N-type electrode 241 and the P-type electrode 242, current flows through the epitaxial layer structure 23, so that electrons and holes are recombined in the epitaxial layer structure 23 and energy is released in the form of light emission. Light propagating through the top surface 234 of the epitaxial-layer structure 23 (i.e., the top surface of the second cladding layer 233) will have various angles of incidence with respect to the top surface 234 to minimize reflection of light back into the epitaxial-layer structure 23 and significantly increase the likelihood of light entering the ambient environment. Likewise, since the roughness of the bottom surface 235 is not less than 100nmrms, light generated from the epitaxial-layer structure 23 traveling toward the bottom surface 235 (i.e., the bottom surface of the first cladding layer 231) will have various incident angles with respect to the bottom surface 235, thereby increasing the chance of light entering the transparent refractive layer 22. At this time, since the transparent refractive layer 22 has a thickness of less than 5 μm and a refractive index between 1 and 2, the transparent refractive layer 22 is an intermediate between the epitaxial layer structure 23 and the mirror layer 212 of the substrate 21. Light is reflected omnidirectionally at the interface between the transparent refractive layer 22 and the mirror layer 212 and then passes through the transparent refractive layer 22 and the epitaxial layer structure 23 into the surrounding environment. Therefore, the brightness of the LED chip is effectively improved.

For a light emitting diode chip having high light extraction efficiency, the electrode unit 24 and the epitaxial-layer structure 23 constitute a current path and effectively dissipate excessive heat generated by the epitaxial-layer structure 23 when light is generated. Conducting heat and current in different paths. The resistance of the device is not affected by the heat dissipation path. Therefore, the present light emitting diode chip is stable in operation and has a long life.

The method for manufacturing the light emitting diode chip 2 of the present invention will be described and explained in detail below.

Referring to fig. 4, the method for manufacturing the light emitting diode chip 2 includes: a step 41 of forming an epitaxial layer structure, a step 42 of performing a first roughening step, a step 43 of forming a pair of electrodes, a step 44 of forming a temporary substrate and removing the substrate under the epitaxial layer structure, a step 45 of performing a second roughening step, a step 46 of forming the substrate under the bottom surface of the first cladding layer of the epitaxial layer structure, and a step 47 of removing the temporary substrate. Thus, the light emitting diode chip 2 having high light extraction is manufactured.

Referring to fig. 5, in step 41, an epitaxial layer structure 23 is formed, where the epitaxial layer structure 23 includes: a GaN-based semiconductor material may be epitaxially grown on the substrate 51, the first clad layer 231, the active layer 232, and the second clad layer 233 on the substrate 51.

Subsequently, in step 42, a first roughening step is performed by an inductively coupled plasma etching method to roughen a surface of the second cladding layer 233 of the epitaxial-layer structure 23 (i.e., the top surface 234 of the epitaxial-layer structure 23) to have a roughness of not less than 100nm rms. In this step, the epitaxial growth method may also be used to directly grow the roughened top surface 234 of the epitaxial-layer structure 23. The first roughening step may also be performed by wet etching or photo-assisted chemical etching methods.

Referring to fig. 4 and 6, step 43 is performed to remove a portion of the epitaxial layer structure 23 to form a mesa thereon. Then, the N-type electrode 241 and the P-type electrode 242 are formed on the first cladding layer 231 and the second cladding layer 233, respectively, and are in ohmic contact with the first cladding layer 231 and the second cladding layer 233, respectively.

Please refer to fig. 4, fig. 7 and fig. 8. When step 44 is performed, a temporary substrate 52 is attached under the second cover layer 233 with wax or removable glue, respectively, as shown in fig. 7. Then, the substrate 51 is removed by a laser lift-off technique, etching, smart cut (smart cut), or the like to expose the bottom surface of the first cladding layer 231 of the epitaxial-layer structure 23, as shown in fig. 8.

Referring to fig. 4 and 9, in step 45, a second roughening step is performed by wet etching to roughen the exposed surface of the first cladding layer 231 to have a roughness of not less than 100nm rms (i.e., to form the bottom surface 235 of the epitaxial-layer structure 23). Likewise, the second roughening step may be performed by wet etching or photo-assisted chemical etching.

Referring to fig. 4 and 10, step 46 is performed to attach the substrate 21 to the roughened surface (i.e., to the bottom surface 232 of the first cladding layer 235 with a glue having a refractive index and transparent to the light generated from the epitaxial-layer structure 23). The glue is cured to become the transparent refractive layer 22, and its thickness is controlled to be not more than 5 μm to obtain optimum optical and thermal properties. The mirror layer 212 may also be first coated on the base silicon substrate 211 to form the substrate 21.

Referring to fig. 3 and 4, finally, in step 47, temporary substrate 52 is removed and residues left on epitaxial layer structure 23, such as wax residues used to attach temporary substrate 52 to epitaxial layer structure 23, are cleaned. Thereby obtaining the light emitting diode chip 2 having high light extraction efficiency.

In the second aspect of the light emitting diode chip of the present invention, glue is applied on the substrate 21 having a U-shaped cross section, and then the epitaxial-layer structure 23 is attached to the substrate 21 having a U-shaped cross section with the glue. The glue is cured to become the transparent refractive layer 22. In addition, the light-emitting diode chip of the second aspect with high light extraction can be manufactured according to the process flow of fig. 12. In step 61, an epitaxial layer structure 23 is formed on an epitaxial substrate. In step 62, the surface of the second cladding layer 233 of the epitaxial-layer structure 23 is roughened to have a roughness of not less than 100nm rms. Mesa portions are formed on the epitaxial-layer structure 23. Then, an N-type electrode 241 and a P-type electrode 242 are separately formed on the epitaxial-layer structure 23. A temporary substrate is attached to the roughened top surface 234 of the epitaxial-layer structure 23. Then, the epitaxial substrate is separated from the epitaxial-layer structure 23. Thereafter, the surface of the first clad layer 231 is roughened by wet etching to have a roughness of not less than 100nm rms. A partially completed light emitting diode chip is shown in fig. 9.

Subsequently, in step 66, a transparent refractive layer 22 is deposited on the bottom surface of the epitaxial-layer structure 23, which transparent refractive layer is transparent to the light generated by the epitaxial-layer structure 23 and has a refractive index between air and the epitaxial-layer structure. The transparent refractive layer 22 has a thickness of not more than 5 μm rms.

Then, in step 67, a seed layer is deposited on the transparent refractive layer 22. Then, an electroplating process is performed to form the substrate 21 from the seed layer. When the seed layer is deposited only on the bottom surface of the transparent refractive layer 22, the substrate 21 is formed as shown in fig. 3. When the seed layer is deposited on the bottom surface and the sidewall of the transparent refractive layer 22, the substrate 21 is formed into a cup holding a chip, as shown in fig. 11. Also, the substrate 21 may include a base substrate 211 and a mirror layer 212, in which a seed layer made of a predetermined material is formed. Then, the seed layer is thickened to form the mirror layer 212. A base substrate 211 is formed under the mirror layer 212. The manufacturing process for forming the substrate 21 including the base substrate 211 and the mirror layer 212 is well known and will not be described here.

Finally, in step 68, the temporary substrate is removed. The epitaxial layer structure 23 is cleaned of residue left thereon (e.g., residue of wax used to attach the temporary substrate to the epitaxial layer structure 23). Thereby, a light emitting diode chip having high light extraction efficiency is obtained.

Fig. 13 is a schematic cross-sectional view of a light-emitting diode chip according to a third aspect of the present invention. The third aspect is different from the above two aspects in that a transparent conductive layer 25 capable of uniformly diffusing current is formed on the top surface 234 of the epitaxial-layer structure 23 to improve the external quantum efficiency of the diode chip. The surface of the transparent conductive layer 25 may be flat or roughened to substantially improve light extraction from the diode chip.

The process for manufacturing the light emitting diode chip of the third aspect differs from the two processes described above in that a transparent conductive layer 25 of Indium Tin Oxide (ITO) is deposited on the roughened top surface 234 of the epitaxial-layer structure 23 after the first roughening steps 42, 62 are performed but before the step 43, 63 of forming a pair of electrodes. The transparent conductive layer 25 of Indium Tin Oxide (ITO) may also be roughened by the above-described method.

The led chip employs the roughened top 234 and bottom 235 surfaces of the epitaxial-layer structure 23 to enhance light extraction from the diode chip. The lenticular refractive layer 22 having a predetermined thickness (as an interface between the epitaxial layer structure 23 and the substrate 21) may more effectively reflect light propagating toward the substrate 21 back toward the top surface 234 to further improve light extraction. The brightness of the diode chip is improved. The present light emitting diode chip and the method of manufacturing the same can actually improve light extraction as compared with the conventional light emitting diode chip 1, 1 'in which light propagating toward the substrate 11, 11' cannot be extracted from the diode chip and is wasted.

The examples given above serve only as aspects of the invention. These examples should not be construed as limiting the scope of practical application of the present invention and, therefore, all modifications and variations (including other aspects) that do not depart from the spirit of the invention and the appended claims should fall within the protected scope of the invention and the claims.

Claims (36)

1. A light emitting diode chip, comprising:

a substrate;

a transparent refractive layer formed on the substrate, the transparent refractive layer having a refractive index greater than that of air;

an epitaxial layer structure having a bottom surface connected to the transparent refractive layer and a top surface opposite to the bottom surface, the epitaxial layer structure generating light and having a refractive index greater than the transparent refractive layer, the bottom surface and the top surface each having a roughness not less than 100nm root mean square rms; and

an electrode unit having a pair of electrodes spaced apart on the epitaxial layer structure to form an ohmic contact with the epitaxial layer structure and to provide electrical energy to the epitaxial layer structure.

2. The light-emitting diode chip as claimed in claim 1, wherein the transparent refractive layer has a thickness of not more than 5 μm rms and the refractive index is between 1 and 2.

3. The light emitting diode chip of claim 1, wherein the transparent refractive layer is formed of a polymer or dielectric material having a thermal conductivity of up to 0.2W/m.k or more.

4. The light emitting diode chip of claim 2, wherein the transparent refractive layer is formed of a polymer or dielectric material having a thermal conductivity of up to 0.2W/m.k or more.

5. The light-emitting diode chip as claimed in claim 1, further comprising a mirror layer having a reflection efficiency of not less than 50% and formed between the substrate and the transparent refractive layer.

6. The light emitting diode chip of claim 1, wherein the substrate is formed of silicon, ceramic, or a metallic material.

7. The light emitting diode chip of claim 5, wherein the mirror layer has a material selected from the group consisting of Al, Ag, Au, Pt, Pd, Rb, and combinations thereof.

8. The light-emitting diode chip as claimed in claim 5, wherein the mirror layer is formed of high-refractive-index dielectric layers and low-refractive-index dielectric layers alternately arranged with each other.

9. The light emitting diode chip of claim 1, wherein the epitaxial layer structure is formed of a GaN-based material and includes an N-type first cladding layer having the bottom surface, a P-type second cladding layer having the top surface, and an active layer sandwiched between the first cladding layer and the second cladding layer.

10. The light-emitting diode chip of claim 1, further comprising: a transparent conductive layer formed on the top surface of the epitaxial layer structure.

11. The light emitting diode chip of claim 10, wherein the transparent conductive layer has a roughened top surface.

12. The light emitting diode chip of claim 1, the substrate being around the transparent refractive layer.

13. A method for manufacturing a light emitting diode chip having high light extraction efficiency, the method comprising:

forming an epitaxial layer structure for generating light by a photoelectric effect on a substrate, the epitaxial layer structure having a first cladding layer of a first conductivity type, a second cladding layer of a second conductivity type, and an active layer sandwiched between the first cladding layer and the second cladding layer;

performing a first roughening step for making a top surface of the second clad layer have a roughness of not less than 100nm rms;

forming a pair of electrodes in ohmic contact with the first clad layer and the second clad layer, respectively;

separately forming a temporary substrate on the second cladding layer and removing the substrate under the epitaxial layer structure to expose a bottom surface of the first cladding layer;

performing a second roughening step for making the bottom surface of the first clad layer have a roughness of not less than 100nm rms;

forming a substrate under the bottom surface of the first cladding layer; and

and removing the temporary substrate.

14. The method for manufacturing a light-emitting diode chip as claimed in claim 13, further comprising: a transparent conductive layer is formed on a top surface of the second cladding layer.

15. The method for manufacturing a light-emitting diode chip as claimed in claim 14, wherein said step for forming said transparent conductive layer further comprises roughening a top surface of said transparent conductive layer.

16. The method for manufacturing a light-emitting diode chip as claimed in claim 13, wherein the first roughening step and the second roughening step are performed by epitaxial growth, wet etching, inductively coupled plasma etching, or photo-assisted chemical etching.

17. The method for manufacturing a light-emitting diode chip as claimed in claim 13, wherein said temporary substrate is attached on said second cladding layer with wax or removable glue.

18. The method for manufacturing a light-emitting diode chip as claimed in claim 13, wherein said substrate is removed by chemical etching, laser lift-off technique or smart cut.

19. The method for manufacturing a light-emitting diode chip as claimed in claim 13, wherein said step for forming a substrate under the bottom surface of said first cladding layer comprises attaching said substrate to said first cladding layer with a glue having a refractive index larger than that of air and smaller than that of said epitaxial-layer structure.

20. The method for manufacturing a light-emitting diode chip as claimed in claim 19, wherein said glue is transparent to light emitted from said epitaxial-layer structure.

21. The method for manufacturing a light-emitting diode chip as claimed in claim 19, wherein the paste has a thickness of not more than 5 μm rms.

22. The method for manufacturing a light-emitting diode chip as claimed in claim 20, wherein the paste has a thickness of not more than 5 μm rms.

23. The method for manufacturing a light-emitting diode chip as claimed in claim 13, wherein the first conductivity type is an N-type or a P-type.

24. A method for manufacturing a light emitting diode chip having high light extraction efficiency, the method comprising:

forming an epitaxial layer structure for generating light by a photoelectric effect on a substrate, the epitaxial layer structure having a first cladding layer of a first conductivity, a second cladding layer of a second conductivity, and an active layer sandwiched between the first cladding layer and the second cladding layer;

performing a first roughening step for making a top surface of the second clad layer have a roughness of not less than 100nm rms;

forming a pair of electrodes in ohmic contact with the first clad layer and the second clad layer, respectively;

separately forming a temporary substrate on the second cladding layer and removing the substrate under the epitaxial layer structure to expose a bottom surface of the first cladding layer;

performing a second roughening step for making the bottom surface of the first clad layer have a roughness of not less than 100nm rms;

forming a transparent refractive layer having a refractive index greater than that of air and less than that of the epitaxial-layer structure, and connected to the first cladding layer;

forming a substrate connected to the transparent refractive layer; and

and removing the temporary substrate.

25. The method for manufacturing a light-emitting diode chip as claimed in claim 24, further comprising: a transparent conductive layer is formed on a top surface of the second cladding layer.

26. The method for manufacturing a light-emitting diode chip as claimed in claim 25, wherein said step for forming said transparent conductive layer further comprises roughening said top surface of said transparent conductive layer.

27. The method for manufacturing a light-emitting diode chip as claimed in claim 24, wherein said first roughening step and said second roughening step are performed by epitaxial growth, wet etching, inductively coupled plasma etching, or photo-assisted chemical etching.

28. The method for manufacturing a light-emitting diode chip as claimed in claim 24, wherein said temporary substrate is attached to said second cladding layer with wax or removable glue.

29. The method for manufacturing a light-emitting diode chip as claimed in claim 24, wherein said substrate is removed by chemical etching, laser lift-off technique or smart cut.

30. The method for manufacturing a light-emitting diode chip as claimed in claim 24, wherein said transparent refractive layer is formed by film deposition.

31. The method for manufacturing a light-emitting diode chip as claimed in claim 24, wherein said step for forming a substrate comprises: a seed layer is formed on the transparent refractive layer using a thin film deposition process, and then an electroplating process is performed to form the substrate from the seed layer.

32. The method for manufacturing a light-emitting diode chip as claimed in claim 24, wherein the first conductivity type is N-type or P-type.

33. The method for manufacturing a light-emitting diode chip as claimed in claim 24, wherein said transparent refractive layer has a thickness of not more than 5 μm rms.

34. The method for manufacturing a light-emitting diode chip as claimed in claim 24, wherein the method further comprises: forming a mirror layer on the transparent refractive layer before the step of forming the substrate.

35. The method for manufacturing a light-emitting diode chip as claimed in claim 34, wherein said mirror layer comprises an electrically conductive material, an electrically insulating material or a combination thereof.

36. The method for manufacturing a light-emitting diode chip as claimed in claim 34, wherein said mirror layer is formed of high-refractive-index dielectric layers and low-refractive-index dielectric layers alternately arranged with each other.