TWI427831B - Led epitaxial structure and manufacturing method - Google Patents

Description

LED epitaxial structure and manufacturing method

The invention relates to an LED epitaxial structure and a manufacturing method thereof, in particular to an LED epitaxial structure and a manufacturing method thereof with better light extraction efficiency.

LED industry is one of the most watched industries in recent years. Since its development, LED products have the advantages of energy saving, power saving, high efficiency, fast response time, long life cycle, mercury free, and environmental benefits. However, since the structure of the LED is epitaxially grown on the sapphire substrate, the lattice constant and the thermal expansion coefficient of the epitaxial and sapphire substrates are greatly different, so a high density Thread Dislocation is generated, and such a high density line difference is generated. The arrangement limits the luminous efficiency of the LED. In addition, in the structure of the LED, in addition to the light absorption layer (Active Layer) and other epitaxial layers will absorb light, the high refractive index of the semiconductor will also limit the light generated by the LED, and often produce total internal reflection for most of the The light emitted from the luminescent layer is confined inside the semiconductor, and this limited light may be absorbed by the thicker substrate. Therefore, how to extract the light source from the luminescent layer of the semiconductor and increase the light extraction efficiency is a problem that the LED industry is currently striving for.

In view of the above, it is necessary to provide an LED epitaxial structure and a manufacturing method with good light extraction efficiency.

LED epitaxial structure and manufacturing method, comprising a substrate, an epitaxial layer and a light Extraction layer. The epitaxial layer is grown on a top surface of the substrate, and the light extraction layer is formed on a surface layer of the epitaxial layer. The light extraction layer has a light extraction surface microstructure layer and a protective layer. The light extraction surface microstructure layer is formed between the light emitting layer and the surface layer of the epitaxial layer, and the protective layer is formed in the structure of the light extraction surface microstructure layer. The surface of the epitaxial layer forms a transparent conductive layer.

A LED epitaxial manufacturing method comprising the steps of: providing a sapphire substrate to grow an epitaxial layer on the sapphire substrate; forming a light extraction surface microstructure layer, wet etching on the surface of the epitaxial layer and illuminating Between the layers; forming a protective layer, forming a light extraction layer in the light extraction surface microstructure layer; forming a transparent conductive layer on the surface of the epitaxial layer; forming electrodes on the epitaxial layer respectively Settings.

In the LED epitaxial structure and the manufacturing method described above, since the light extraction surface microstructure formed by the light extraction layer is caused by a wet etching mechanism etching defect, the microstructure density is denser, and the microstructure can be modulated with the defect. The density, therefore, can effectively improve the light extraction efficiency, and the molding manufacturing method of the light extraction surface microstructure layer has a lower manufacturing cost than the current molding method, and has a competitive advantage.

10, 20‧‧‧LED epitaxial structure

12, 22‧‧‧ substrate

14, 24‧‧‧ epitaxial layer

16, 26‧‧‧Light extraction layer

18‧‧‧ Buffer layer

30‧‧‧ lattice defects

122, 222‧‧‧ top

124, 224‧‧‧ bottom

142, 246‧‧‧N type epitaxial layer

144, 244‧‧ ‧ luminescent layer

146, 242‧‧‧P type epitaxial layer

148‧‧‧Transparent conductive layer

162, 262‧‧‧ light extraction surface microstructure layer

164, 264‧‧ ‧ protective layer

1422, 2462‧‧‧N type electrode

1462‧‧‧P type electrode

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view showing a first embodiment of the LED epitaxial structure of the present invention.

Figure 2 is a cross-sectional view showing a second embodiment of the LED epitaxial structure of the present invention.

3 is a flow chart showing the steps of the LED epitaxial structure and the manufacturing method of the present invention.

4 is a cross-sectional view corresponding to the step of growing the epitaxial layer of the substrate of FIG. 3.

Figure 5 is a cross-sectional view showing the steps of forming a light extraction surface microstructure layer corresponding to Figure 3.

Figure 6 is a cross-sectional view showing the steps of forming a protective layer corresponding to Figure 3.

Figure 7 is a cross-sectional view showing the step of forming a transparent conductive layer corresponding to Figure 3.

The present invention will be specifically described below with reference to the accompanying drawings.

Referring to FIG. 1 , a cross-sectional view of a first embodiment of an LED epitaxial structure according to the present invention is shown. The LED epitaxial structure 10 includes a substrate 12 , an epitaxial layer 14 , and a light extraction layer 16 . The substrate 12 includes a top surface 122 and a bottom surface 124. The substrate 12 is a sapphire substrate, and the epitaxial layer 14 is grown on the top surface 122. The epitaxial layer 14 is sequentially grown from the top surface 122 to have an N-type epitaxial layer 142, a light-emitting layer 144, and a P-type epitaxial layer 146, wherein the top surface 122 and the epitaxial layer 14 are There is further a buffer layer 18. The buffer layer 18 can adjust the difference in lattice matching between the epitaxial layer 14 and the substrate 12, so that the epitaxial structure 10 causes lattice defects 30 due to stress factors of lattice difference (as shown in FIG. 4). The density can be adjusted. The lattice defect 30 reduces the electron-hole combination probability and reduces the luminous efficiency in the light-emitting layer 144, so that the lattice defect density of the epitaxial structure 10 needs to be adjusted to avoid affecting the light-emitting efficiency of the epitaxial structure 10. . In this embodiment, in addition to the buffer layer 18 adjusting the density of the lattice defects 30 of the epitaxial structure 10, the light extraction layer 16 is formed on the surface layer of the epitaxial layer 14 for increasing the luminous efficacy. The light extraction layer 16 has a light extraction surface microstructure layer 162 and a protective layer 164. The light extraction surface microstructure layer 162 is formed between the light emitting layer 144 of the epitaxial layer 14 and the surface layer. In this embodiment, the surface layer of the epitaxial layer 14 is a P-type epitaxial layer 146. In other words, the light extraction surface microstructure layer 162 is formed on the light emitting layer 144 and the P-type Lei Between the layers 146. The light extraction surface microstructure of the light extraction surface microstructure layer 162 is deep down to the light emitting layer 144 by the surface of the epitaxial layer 14 (P-type epitaxial layer 146) in an inverted cone shape (not shown). Forming a concave-convex surface layer. The uneven surface layer can destroy the total reflection inside the epitaxial structure 10 to extract light to increase the luminosity. The protective layer 164 is formed in the concave-convex surface layer of the light extraction surface microstructure layer 162. The material of the protective layer 164 may be cerium oxide SiO2, cerium nitride SiN or germanium oxynitride SiOxNy. The surface of the epitaxial layer 14 is further formed with a transparent conductive layer 148 for assisting current dispersion. The material of the transparent conductive layer 148 may be ITO (Indium Tin Oxide), nickel/gold Ni/Au or the like. The transparent conductive layer 148 has a P-type electrode 1462. The N-type epitaxial layer 142 has an N-type electrode 1422 for guiding the power required for the LED epitaxial structure 10 to emit light.

Referring to FIG. 2, a cross-sectional view of a second embodiment of the LED epitaxial structure of the present invention is shown. The LED epitaxial structure 20 includes a substrate 22, an epitaxial layer 24, and a light extraction layer 26. The substrate 22 includes a top surface 222 and a bottom surface 224. The substrate 22 is a metal substrate. The epitaxial layer 24 is disposed on the top surface 222 of the metal substrate 22. The epitaxial layer 24 can be separately formed by laser, chemical, mechanical, or the like, and bonded to the metal substrate 22 via electroplating or other bonding to form a vertical light emitting diode structure. The top surface 222 is sequentially grown to have a P-type epitaxial layer 242, a light-emitting layer 244, and an N-type epitaxial layer 246. The surface layer of the epitaxial layer 24 forms a light extraction layer 26. The light extraction layer 26 has a light extraction surface microstructure layer 262 and a protective layer 264. The light extraction surface microstructure layer 262 is formed between the light emitting layer 244 of the epitaxial layer 24 and the surface layer, which is the same as the light extraction layer 16 of the first embodiment. The difference is that the surface layer of the epitaxial layer 24 is an N-type epitaxial layer 246. Therefore, in the embodiment, the light extraction surface microstructure layer 262 is formed between the light emitting layer 244 and the N type epitaxial layer 246. The N-type epitaxial layer 246 has a small resistance value, so this embodiment may not require forming a transparent conductive layer. The N-type Lei The crystal layer 246 has an N-type electrode 2462 thereon, and the metal substrate 22 constitutes a vertical structure of the LED epitaxial structure 20.

The LED epitaxial manufacturing method of the present invention (shown in FIG. 3) comprises the following steps: S11 provides a sapphire substrate to grow an epitaxial layer on the sapphire substrate; S12 forms a light extraction surface microstructure layer, in a wet manner Etching is performed between the surface of the epitaxial layer and the light-emitting layer; S13 forms a protective layer, and a light extraction layer is formed in the light extraction surface microstructure layer; S14 forms a transparent conductive layer in the epitaxial layer Surfaces; and S15 to form electrodes, which are respectively disposed on the epitaxial layer.

The step S11 provides a sapphire substrate 12 (shown in FIG. 4). The epitaxial layer 14 is grown on the sapphire substrate 12. The epitaxial layer 14 includes the N-type epitaxial layer 142, the luminescent layer 144, and the P-type Lei. The crystal layer 146, wherein the buffer layer 18 is formed between the sapphire substrate 12 and the epitaxial layer 14. The buffer layer 18 can adjust the density of the defects 30 of the epitaxial layer 14. This step S12 forms a light extraction surface microstructure layer 162 (shown in FIG. 5), which can be performed by wet chemical etching using potassium KOH hydroxide or H3PO4 phosphoric acid. In this embodiment, KOH potassium hydroxide wet chemistry is used. Etching, using the defect 30 of the epitaxial layer 14 to perform a bonding reaction, not only to remove the defect 30 of the epitaxial layer 14, but the buffer layer 18 can adjust the density of the defect 30 to form the light. The etching density of the extraction surface microstructure layer 162 also increases. The increased etching density of the light extraction surface microstructure layer 162 can increase the light extraction efficiency. The etching depth of the light extraction surface microstructure layer 162 reaches the light emitting layer 144 from the surface of the epitaxial layer 14. Then, in step S13, a protective layer 164 (shown in FIG. 6) is formed. In the light extraction surface microstructure layer 162, the light extraction surface is micro-junctioned. The layer 162 forms the light extraction layer 16. Immediately after the step S14, a transparent conductive layer 148 is formed (as shown in FIG. 7). The protective layer 164 on the surface of the epitaxial layer 14 is removed by chemical mechanical polishing or chemical etching, and the transparent conductive layer 148 is formed. The surface of the epitaxial layer 14 is in contact with the P-type epitaxial layer 146. Finally, the step S15 is performed to form the electrodes 1462 and 1422, and the P-type electrode 1462 is disposed on the transparent conductive layer 148 of the P-type epitaxial layer 146 by a yellow lithography process, and the P-type electrode 1462 is disposed on the N-type epitaxial layer 142. N-type electrode 1422. The electrode 1462, 1422 material may be chromium/gold Cr/Au or the like.

In summary, in the LED epitaxial structure and manufacturing method of the present invention, the surface layer of the epitaxial layer 14 forms the light extraction layer 16. The light extraction layer 16 is performed by wet chemical etching, and has good performance at a low cost and a high microstructure density on the light extraction surface. The epitaxial layer 14 may affect the defect 30 part of the luminous efficacy, and may also disappear due to the wet chemical etching manufacturing method and the mechanism for the protective layer to fill the dangling bond, and may add additional light in and out and change the light angle to effect Improve luminous efficiency.

It should be noted that the above-described embodiments are merely preferred embodiments of the present invention, and those skilled in the art can make other changes within the spirit of the present invention. Such changes in accordance with the spirit of the invention are intended to be included within the scope of the invention.

10‧‧‧LED epitaxial structure

12‧‧‧Substrate

14‧‧‧ epitaxial layer

16‧‧‧Light extraction layer

18‧‧‧ Buffer layer

122‧‧‧ top surface

124‧‧‧ bottom

142‧‧‧N type epitaxial layer

144‧‧‧Lighting layer

146‧‧‧P type epitaxial layer

148‧‧‧Transparent conductive layer

162‧‧‧Light extraction surface microstructure layer

164‧‧ ‧ protective layer

1422‧‧‧N type electrode

1462‧‧‧P type electrode

Claims (13)

An LED epitaxial structure includes a substrate, an epitaxial layer, and a light extraction layer, wherein the epitaxial layer is grown on a top surface of the substrate, wherein the light extraction layer is formed on a surface layer of the epitaxial layer, The light extraction layer has a light extraction surface microstructure layer and a protective layer formed between the light emitting layer and the surface layer of the epitaxial layer and the light extraction surface of the light extraction surface microstructure layer The surface of the epitaxial layer is inverted from the surface of the epitaxial layer into the luminescent layer to form a concave-convex surface layer. The protective layer is formed in the structure of the light-extracting surface microstructure layer, and the surface of the epitaxial layer forms a transparent conductive layer. Floor. The LED epitaxial structure according to claim 1, wherein the substrate comprises a top surface and a bottom surface, and the top surface and the epitaxial layer further have a buffer layer. The LED epitaxial structure according to claim 2, wherein the substrate is a sapphire substrate. The LED epitaxial structure according to claim 1, wherein the epitaxial layer has an N-type epitaxial layer, the luminescent layer and a P-type epitaxial layer sequentially grown from a top surface thereof. The P-type epitaxial layer is the surface layer of the epitaxial layer. The LED epitaxial structure according to claim 1, wherein the material of the protective layer is cerium oxide SiO2, cerium nitride SiN or germanium oxynitride SiOxNy. The LED epitaxial structure according to claim 1, wherein the transparent conductive layer has a P-type electrode thereon. The LED epitaxial structure according to claim 6, wherein the transparent conductive layer is made of ITO (Indium Tin Oxide) or nickel/gold Ni/Au. The LED epitaxial structure according to claim 1, wherein the substrate is a metal substrate having an epitaxial layer on a top surface thereof, and a surface layer of the epitaxial layer forms a light extraction layer. The LED epitaxial structure according to claim 8, wherein the top surface of the epitaxial layer has a P-type epitaxial layer, a light-emitting layer and an N-type epitaxial layer. The LED epitaxial structure according to claim 8, wherein the light extraction surface microstructure layer of the light extraction layer is formed between the light emitting layer and the N-type epitaxial layer, the N-type epitaxial layer There is an N-type electrode on it. An epitaxial fabrication method comprising the steps of: providing a sapphire substrate to grow an epitaxial layer on the sapphire substrate; etching from the surface layer of the epitaxial layer to the luminescent layer by wet etching to expose the epitaxial layer Forming a concavo-convex surface layer from the surface of the layer and the light-emitting layer to the surface of the epitaxial layer with an inverted cone shape down into the light-emitting layer; forming a protective layer, forming a light in the microstructure layer of the light extraction surface An extraction layer is formed on the surface of the epitaxial layer; electrodes are formed on the epitaxial layer. The LED epitaxial manufacturing method according to claim 11, wherein the epitaxial layer is grown on the sapphire substrate, the epitaxial layer comprises the N-type epitaxial layer, the luminescent layer, and the P-type epitaxial layer The buffer layer is formed between the sapphire substrate and the epitaxial layer. The LED epitaxial manufacturing method according to claim 11, wherein the step of forming the light extraction surface microstructure layer is wet chemical etching using KOH potassium hydroxide.