NITRIDE SEMICONDUCTOR LIGHT-EMITTTING DEVICE AND PROCESS FOR PRODUCING THE SAME
Provided are a nitride semiconductor light-emitting device comprising a polycrystalline or amorphous substrate made of AlN; a plurality of dielectric patterns formed on the AlN substrate and having a stripe or lattice structure; a lateral epitaxially overgrown-nitride semiconductor layer formed on the AlN substrate having the dielectric patterns by Lateral Epitaxial Overgrowth; a first conductive nitride semiconductor layer formed on the nitride semiconductor layer; an active layer formed on the first conductive nitride semiconductor layer; and a second conductive nitride semiconductor layer formed on the active layer; and a process for producing the same.
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1. Field of the Invention
The present invention relates to a nitride semiconductor light-emitting device, and more particularly to a nitride semiconductor light-emitting device having an AlN polycrystalline or amorphous substrate and a process for producing the same.
2. Description of the Related Art
Generally, a great deal of attention has been directed to nitride semiconductor crystals as a material for use in preparing visible and ultraviolet light LEDs and blue-green color optical devices such as light-emitting diodes or laser diodes, because they produce light with a broad spectrum including the entire visible light region and also the ultraviolet light region.
In order to prepare a high efficiency optical device with such nitride semiconductor crystals, there is essentially required a technique which enables a nitride semiconductor to grow into a high quality single crystal thin film. However, the III-A group nitride semiconductors are not suitable for general substrates due to their lattice constant and thermal expansion coefficient and thus have a difficulty in growing a single crystal thin film.
To grow nitride semiconductor crystals, a sapphire (Al2O3) or SiC substrate is limitedly employed only. For example, nitride semiconductor crystals may be grown on the sapphire substrate by heteroepitaxy methods using Metal Organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), and the like.
But, despite use of such a nitride semiconductor single crystal substrate, it is difficult to directly grow a high quality nitride semiconductor single crystal on the substrate due to inconsistency of a lattice constant and a thermal expansion coefficient therebetween, and thus a low temperature nucleus-growth layer and a buffer layer are additionally used.
As shown in
Further, a buffer layer was formed on the sapphire substrate in order to grow high quality nitride semiconductor crystals. As the buffer layer, a low temperature nucleus-growth layer such as AlxGa1-xN wherein x is between 0 and 1, is usually used.
However, even when a nitride semiconductor single crystal was grown on the sapphire substrate after forming the low temperature nucleus-growth layer, the nitride semiconductor single crystal had crystal defects of about 109 to about 1010 cm−2. In particular, these crystal defects propagate in the vertical direction and thus exhibit adverse effects responsible for leakage of electrical current.
On the other hand, the conventional sapphire or SiC substrate may have disadvantages of high cost, lower thermal conductivity, and lower mechanical properties, resulting in increased production costs and deterioration of device characteristics, as compared to an AlN polycrystalline or amorphous substrate. But, the AlN polycrystalline or amorphous substrate is not suitable for growth of the nitride single crystal layer and thus is not usually used as a substrate for the nitride semiconductor light-emitting device.
SUMMARY OF THE INVENTIONTherefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a nitride semiconductor light-emitting device comprising a high quality nitride semiconductor layer grown on an AlN polycrystalline or amorphous substrate by Lateral Epitaxial Overgrowth (LEO).
It is another object of the present invention to provide a process for producing a nitride semiconductor light-emitting device comprising the step of forming a high quality nitride semiconductor layer on an AlN polycrystalline or amorphous substrate by using LEO.
In accordance with the present invention, the above and other objects can be accomplished by the provision of a nitride semiconductor light-emitting device comprising:
a polycrystalline or amorphous substrate made of AlN;
a plurality of dielectric patterns formed on the AlN substrate and having a stripe or lattice structure;
a lateral epitaxially overgrown-nitride semiconductor layer formed on the AlN substrate having the dielectric patterns by Lateral Epitaxial Overgrowth (LEO);
a first conductive nitride semiconductor layer formed on the nitride semiconductor layer;
an active layer formed on the first conductive nitride semiconductor layer; and
a second conductive nitride semiconductor layer formed on the active layer.
Preferably, the AlN substrate has an upper surface having irregularities formed to face in a predetermined direction.
The nitride semiconductor light-emitting device may further include a buffer layer formed on the AlN substrate. Preferably, the buffer layer may be a low temperature nucleus-growth layer made of a material having the formula of AlxGa1-xN wherein x is between 0 and 1.
Preferably, the buffer layer has an upper surface having irregularities formed in a predetermined face direction.
Dielectric patterns used in the present invention may be made of SiO2 or SiN. The lateral epitaxially overgrown-nitride semiconductor layer may be formed of the nitride semiconductor layer containing first conductive impurities and then may be provided as a clad layer having the same conductivity-type as that of the first conductive nitride semiconductor layer.
The first conductive nitride semiconductor layer may be a p-type nitride semiconductor layer. The second conductive nitride semiconductor layer may be an n-type nitride semiconductor layer. In this case, an n-type nitride semiconductor layer with a relatively low electrical resistance is used as a capping layer and thus a transparent electrode layer for ohmic contact may be eliminated.
Further, the present invention provides a process for producing a novel nitride semiconductor light-emitting device.
The above-mentioned process comprises the steps of:
providing a polycrystalline or amorphous substrate made of AlN;
forming a plurality of dielectric patterns having a stripe or lattice structure on the AlN substrate;
forming a lateral epitaxially overgrown-nitride semiconductor layer on the AlN substrate having the dielectric patterns by Lateral Epitaxial Overgrowth (LEO);
forming a first conductive nitride semiconductor layer on the nitride semiconductor layer;
forming an active layer on the first conductive nitride semiconductor layer; and
forming a second conductive nitride semiconductor layer on the active layer.
Preferably, the process may further comprise the step of etching the upper surface of the AlN substrate such that irregularities are formed on the AlN substrate in a predetermined face direction. The etching step may include a step of applying wet etching to the AlN substrate using an etching solution containing NaOH.
The process may further comprise the step of forming a buffer layer on the AlN substrate, prior to forming the dielectric patterns. Preferably, the buffer layer may be a low temperature nucleus-growth layer made of a material having the formula of AlxGa1-xN wherein x is between 0 and 1. In accordance with the present invention, the process may further comprise the step of etching the upper surface of the buffer layer such that irregularities are formed on the buffer layer in a predetermined face direction.
Further, the dielectric patterns may be made of SiO2 or SiN. The lateral epitaxially overgrown-nitride semiconductor layer may be a nitride semiconductor layer containing first conductive impurities. The first conductive nitride semiconductor layer may be a p-type nitride semiconductor layer. The second conductive nitride semiconductor layer may be an n-type nitride semiconductor layer.
Where the lateral epitaxially overgrown-nitride semiconductor layer is a nitride semiconductor layer containing Al, the step of forming the lateral epitaxially overgrown-nitride semiconductor layer may comprise the step of forming the lateral epitaxially overgrown-nitride semiconductor layer by LEO while injecting Cl- or Br-based gas. As the Br- or Cl-based gas, a gas containing at least one selected from the group consisting of Br2, Cl2, CBr4, CCl4, HBr and HCl may be used.
The present invention provides a new type of nitride semiconductor device by forming a nitride semiconductor layer on AlN polycrystalline or amorphous substrate in place of a conventional sapphire or SiC substrate. That is, a high quality nitride semiconductor layer may be grown by Lateral Epitaxial Overgrowth using dielectric patterns having a stripe or lattice structure. More preferably, a higher quality nitride semiconductor layer may be grown by applying a given etching solution such as NaOH to the AlN polycrystalline or amorphous substrate to form irregularities facing a desired direction.
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Now, the present invention will be described in detail with reference to the attached drawings.
A nitride semiconductor light-emitting device 20 includes an AlN polycrystalline substrate 21. The AlN substrate 21 may comprise Ga and/or In, resulting in (GaIn)AlN. The AlN polycrystalline substrate 21 was provided with a plurality of dielectric patterns 23 having a stripe or lattice structure which were arranged side by side. The AlN polycrystalline substrate 21 having the dielectric patterns formed thereon was provided with a lateral epitaxially overgrown-nitride semiconductor layer 24 grown by Lateral Epitaxial Overgrowth (LEO). On the nitride semiconductor layer 24 were sequentially formed an n-type nitride semiconductor layer 25, an active layer 26 having a multiple-well structure and a p-type nitride semiconductor layer 27.
Further, a transparent electrode layer 28 such as Ni/Au was formed on the p-type nitride semiconductor layer 27 in order to decrease contact resistance. Each of p- and n-electrodes 29b and 29a was provided on the transparent electrode layer 28 and the n-type nitride semiconductor layer 25.
The lateral epitaxially overgrown-nitride semiconductor layer 24 formed on the AlN polycrystalline substrate 21 was formed by LEO using dielectric patterns 23 having a stripe or lattice structure. Therefore, since crystals grow onto the dielectric patterns 23 in the lateral direction, defects progressing in the vertical direction, i.e. the potentials occurring between the interface of heterologous materials may be greatly reduced, unlike a conventional growth method. Therefore, by decreasing potentials which propagate to an active layer, leakage of electric current due to the crystal defects may be significantly reduced. These dielectric patterns may be made of SiO2 or SiN.
The lateral epitaxially overgrown-nitride semiconductor layer 24 used in the present invention may be formed of an undoped nitride semiconductor layer. Alternatively, the layer 24 may also be formed of a nitride semiconductor layer having the same conductivity-type as that of the nitride semiconductor layer 25 formed on the upper part thereof.
For example, in this embodiment, the n-type lateral epitaxially overgrown-nitride semiconductor layer 24 may be formed by injecting n-type impurities to cause lateral epitaxial overgrowth, and may constitute an n-clad layer in integrated form with the n-type nitride semiconductor layer 25 formed on the upper part thereof.
Further, unlike this embodiment, a structure having a p-type nitride semiconductor layer disposed between an AlN polycrystalline substrate and an active layer, and the n-type nitride semiconductor layer disposed on the upper part of the active layer may be also provided. In this case, the n-type nitride semiconductor layer has a relatively low electrical resistance compared to the p-type nitride semiconductor layer.
Thus, a transparent electrode structure 28 formed on the upper part of the p-type nitride semiconductor layer 27 as shown in
First, as shown in
As can be seen from
Then, as shown in
Next, as shown in
Thereafter, as shown in
Then, as shown in
Finally, the n-type nitride semiconductor layer 37 and the active layer 36 were mesa etched to expose a portion thereof, a first electrode 39a was formed on a region of the exposed p-type nitride semiconductor layer 35, and then an n- type electrode 39b such as Ni/Au was formed on the upper surface of the n-type nitride semiconductor layer 37.
Alternatively, still another embodiment may be implemented by first forming a p-type nitride semiconductor layer on an AlN polycrystalline substrate, forming an active layer on the p-type nitride semiconductor layer, and then forming an n-type nitride semiconductor layer on the active layer.
As apparent from the above description, the present invention provides an inexpensive nitride semiconductor light-emitting device having superior characteristics, by forming a high quality nitride semiconductor layer on the substrate by LEO using an AlN polycrystalline or amorphous substrate having superior thermal conductivity and mechanical properties.
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
Claims
1-9. (canceled)
10. A process for producing a nitride semiconductor light-emitting device, comprising the steps of:
- providing a polycrystalline or amorphous substrate made of AlN;
- forming a plurality of dielectric patterns having a stripe or lattice structure on the AlN substrate;
- forming a lateral epitaxially overgrown-nitride semiconductor layer on the AlN substrate having the dielectric patterns by Lateral Epitaxial Overgrowth;
- forming a first conductive nitride semiconductor layer on the nitride semiconductor layer;
- forming an active layer on the first conductive nitride semiconductor layer; and
- forming a second conductive nitride semiconductor layer on the active layer.
11. The process as set forth in claim 10, wherein the substrate comprises (GaIn)AlN substrate.
12. The process as set forth in claim 10, wherein the AlN substrate is a polycrystalline substrate, and the process further comprises the step of etching the upper surface of the AlN substrate such that irregularities having a predetermined face direction are formed on the AlN polycrystalline substrate.
13. The process as set forth in claim 10, wherein the etching step is a step of applying wet etching to the AlN substrate using an etching solution containing NaOH.
14. The process as set forth in claim 10, further comprising:
- forming a buffer layer on the AlN substrate, prior to forming the dielectric patterns.
15. The process as set forth in claim 14, wherein the buffer layer is a low temperature nucleus-growth layer made of a material having a formula of AlxGa1-xN wherein x is between 0 and 1.
16. The process as set forth in claim 12, wherein the process further comprises the step of etching the upper surface of the buffer layer such that irregularities having a predetermined face direction are formed thereon.
17. The process as set forth in claim 16, wherein the etching step is a step of applying wet etching to the buffer layer using an etching solution containing NaOH.
18. The process as set forth in claim 10, wherein the dielectric patterns are made of SiO2 or SiN.
19. The process as set forth in claim 10, wherein the lateral epitaxially overgrown-nitride semiconductor layer is a nitride semiconductor layer containing first conductive impurities.
20. The process as set forth in claim 10, wherein the first conductive nitride semiconductor layer is an n-type nitride semiconductor layer, and the second conductive nitride semiconductor layer is a p-type nitride semiconductor layer.
21. The process as set forth in claim 10, wherein the lateral epitaxially overgrown-nitride semiconductor layer is a nitride semiconductor layer containing Al, and the step of forming the lateral epitaxially overgrown-nitride semiconductor layer is a step of forming the lateral epitaxially overgrown-nitride semiconductor layer using Lateral Epitaxial Overgrowth while injecting Cl- or Br-based gas.
22. The process as set forth in claim 20, wherein the Br- or Cl-based gas is gas containing at least one selected from the group consisting of Br2, Cl2, CBr4, CCl4, HBr and HCl.
Type: Application
Filed: Jan 10, 2014
Publication Date: May 8, 2014
Applicant: SAMSUNG ELECTRONICS CO., LTD. (Seoul)
Inventors: Dong Hyun CHO (Dalsung-gun), Masayoshi KOIKE (Suwon), Yuji IMAI (Suwon), Min Ho KIM (Suwon), Bang Won OH (Sungnam), Hun Joo HAHM (Sungnam)
Application Number: 14/152,980