Semiconductor light-emitting device with selectively formed buffer layer on substrate

The invention discloses a semiconductor light-emitting device and a method of fabricating the same. The semiconductor light-emitting device according to the invention includes a substrate, a buffer layer, a multi-layer structure, and an ohmic electrode structure. The buffer layer is selectively formed on an upper surface of the substrate such that the upper surface of the substrate is partially exposed. The multi-layer structure is formed to overlay the buffer layer and the exposed upper surface of the substrate. The multi-layer structure includes a light-emitting region. The buffer layer assists a bottom-most layer of the multi-layer structure in lateral and vertical epitaxial growth. The ohmic electrode structure is formed on the multi-layer structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor light-emitting device and, more particularly, to a semiconductor light-emitting device with an enhanced external quantum efficiency and a good epitaxy quality.

2. Description of the Prior Art

The current semiconductor light-emitting devices, such as light-emitting diodes, have been used for a wide variety of applications, e.g. illuminations and remote controls. To ensure high functional reliability as great as possible and a low power requirement of the semiconductor light-emitting devices, the external quantum efficiency is required for the devices.

In principle, the external quantum efficiency of a semiconductor light-emitting device is determined both by the internal quantum efficiency and extraction efficiency. The internal quantum efficiency is determined by the material property and quality. The extraction efficiency refers to the proportion of radiation emitted from the interior of the device into the surrounding air or encapsulating epoxy. The extraction efficiency is determined by the losses occurred when radiation leaves the interior of the device. One of the main causes for such losses is the high refractive index of the semiconductor material so the radiation cannot be emitted outside at the semiconductor surface on account of total reflection.

Please refer toFIG. 1. To enhance the external quantum efficiency of the semiconductor light-emitting device, a sapphire substrate1with a patterned surface10has been disclosed and applied to the manufacture of the semiconductor light-emitting device.FIG. 1illustrates a schematic view of a conventional sapphire substrate1with a patterned surface10. The patterned surface10is for scattering light emitted out from the semiconductor light-emitting device to reduce the probability of a total reflection, and further to enhance the external quantum efficiency of the semiconductor light-emitting device.

Although a semiconductor material layer, e.g. a GaN layer, can be formed on the patterned surface10of the sapphire substrate1through a good lateral epitaxial growth, the GaN layer can not be grown on the patterned surface10of the sapphire substrate1directly, i.e. a poor vertical epitaxial growth. Therefore, the quality of the GaN semiconductor material layer formed on the patterned surface10of the sapphire substrate1is still required for improvement.

Inside the semiconductor light-emitting device of the prior art, a buffer layer can be formed between a semiconductor material layer and an ordinary substrate to improve the quality of the semiconductor material layer. As a result, the external quantum efficiency of the semiconductor light-emitting device will further be enhanced by the buffer layer.

Accordingly, the main scope of the invention is to provide a semiconductor light-emitting device with an enhanced external quantum efficiency and a good epitaxy quality.

SUMMARY OF THE INVENTION

One scope of the invention is to provide a semiconductor light-emitting device and a fabricating method thereof.

According to an embodiment of the invention, the semiconductor light-emitting device includes a substrate, a buffer layer, a multi-layer structure, and an ohmic electrode structure.

The buffer layer is selectively formed on an upper surface of the substrate such that the upper surface of the substrate is partially exposed. The multi-layer structure is formed to overlay the buffer layer and the exposed upper surface of the substrate. The multi-layer structure includes a light-emitting region. The buffer layer is formed to assist a bottom-most layer of the multi-layer structure in lateral and vertical epitaxial growth. The ohmic electrode structure is formed on the multi-layer structure.

According to another embodiment of the invention, it is related to a method of fabricating a semiconductor light-emitting device.

First, a substrate is prepared. Subsequently, a buffer layer is formed on an upper surface of the substrate selectively such the upper surface of the substrate is partially exposed. Then, a multi-layer structure is formed to overlay the buffer layer and the exposed upper surface of the substrate. The multi-layer structure includes a light-emitting region, and the buffer layer is formed to assist a bottom-most layer of the multi-layer structure in lateral and vertical epitaxial growth. Finally, an ohmic electrode structure is formed on the multi-layer structure.

Compared to the prior art, the buffer layer of the semiconductor light-emitting device according to the invention is selectively formed on the substrate and is for scattering light emitted from the semiconductor light-emitting device to reduce the total reflection and further enhance the external quantum efficiency of the semiconductor light-emitting device. Furthermore, the buffer layer can assist a bottom-most layer of the multi-layer structure in lateral and vertical epitaxial growth to increase the epitaxy quality of the semiconductor light-emitting device.

DETAILED DESCRIPTION OF THE INVENTION

Please refer toFIG. 2.FIG. 2illustrates a sectional view of a semiconductor light-emitting device2according to an embodiment of the invention. As shown inFIG. 2, the semiconductor light-emitting device2includes a substrate20, a buffer layer22, a multi-layer structure24, and an ohmic electrode structure26.

The buffer layer22is selectively formed on an upper surface200of the substrate20such that the upper surface200of the substrate20is partially exposed. The multi-layer structure24is formed to overlay the buffer layer22and the exposed upper surface200of the substrate20. The multi-layer structure24includes a light-emitting region242. The buffer layer22is formed to assist a bottom-most layer240of the multi-layer structure24in lateral and vertical epitaxial growth. In one embodiment, the bottom-most layer240can be made of GaN. The ohmic electrode structure26is formed on the multi-layer structure24.

In practical applications, the buffer layer22can be made of ZnO, MgxZn1-xO, AlN or Al2O3, where 0<x≦1. In addition, the buffer layer22can have a thickness in a range of 10 nm to 500 nm.

If the buffer layer22is made of ZnO, the precursors of the ZnO buffer layer22can be ZnCl2, ZnMe2, ZnEt2, and H2O, O3, O2plasma, or an oxygen radical. If the buffer layer22is made of MgxZn1-xO, the precursors of the MgxZn1-xO buffer layer22can be ZnCl2, ZnMe2, ZnEt2, MgCp2, Mg(thd)2, and H2O, O3, O2plasma, or an oxygen radical. If the buffer layer22is made of AlN, the precursors of the AlN buffer layer22can be NH3and AlCl3, AlMe3, AlEt3, Me3N:AlH3, or Me2EtN:AlH3. If the buffer layer22is made of Al2O3, the precursors of the Al2O3buffer layer22can be the precursors of Al2O3are AlCl3, AlBr3, AlMe3, AlEt3, and H2O, O3, O2plasma, or an oxygen radical.

In one embodiment, the buffer layer22can be formed by an atomic layer deposition process and/or a plasma-enhanced (or a plasma-assisted) atomic layer deposition process. Moreover, the formation of the buffer layer22can be performed at a processing temperature ranging from room temperature to 1200° C. Further, the buffer layer22can be annealed at a temperature ranging from 400° C. to 1200° C. In another embodiment, the formation of the buffer layer22can be through a selective etching process.

Please refer toFIGS. 3A through 3I.FIGS. 3A through 3Iillustrate sectional views to describe a method of fabricating a semiconductor light-emitting device according to another embodiment of the invention.

First, a substrate20is prepared, as shown inFIG. 3A. Subsequently, as shown inFIG. 3B, a buffer layer22can be formed on an upper surface200of the substrate20by an atomic layer deposition process in one embodiment. Then, an etching-resistant layer (e.g. a photoresist layer)23can be selectively formed on the surface of the buffer layer22as shown inFIG. 3C, and a selective etching process is performed on the surface of the buffer layer22. Accordingly, the buffer layer22can be selectively formed on the upper surface200of the substrate20such that the upper surface200of the substrate20is partially exposed, as shown inFIG. 3D.

In another embodiment, an etching-resistant layer (e.g. a photoresist layer)23can be formed on the upper surface200of the substrate20, as shown inFIG. 3E. Next, a buffer layer22can be formed on the upper surface200of the substrate20by an atomic layer deposition process and/or a plasma-enhanced (or a plasma-assisted) atomic layer deposition process, as shown inFIG. 3F. Then, a lift-off process can be implemented to remove the etching-resistant layer23to selectively form the buffer layer22on the upper surface200of the substrate20such that the upper surface200of the substrate20is partially exposed, as shown inFIG. 3G.

Subsequently, a multi-layer structure24is formed to overlay the buffer layer22and the exposed upper surface200of the substrate20, as shown inFIG. 3H. The multi-layer structure24includes a light-emitting region242, and the buffer layer22is formed to assist a bottom-most layer240of the multi-layer structure24in lateral and vertical epitaxial growth. Finally, the multi-layer structure24can be selectively etched, and then an ohmic electrode structure26is formed on the multi-layer structure24, as shown inFIG. 3I.

Compared to the prior art, the buffer layer of the semiconductor light-emitting device according to the invention is selectively formed on the substrate and for scattering light emitted from the semiconductor light-emitting device to reduce the total reflection and further enhance the external quantum efficiency of the semiconductor light-emitting device. Furthermore, the buffer layer can assist a bottom-most layer of the multi-layer structure in lateral and vertical epitaxial growth to increase the epitaxy quality of the semiconductor light-emitting device.