NITRIDE SEMICONDUCTOR STRUCTURE

Abstract

A nitride semiconductor structure and a semiconductor light emitting device including the same are revealed. The nitride semiconductor structure includes a multiple quantum well structure formed by a plurality of well layers and barrier layers stacked alternately. One well layer is disposed between every two barrier layers. The barrier layer is made of Al.sub.xIn.sub.yGa.sub.1-x-yN (0<x<1, 0<y<1, 0<x+y<1) while the well layer is made of In.sub.zGa.sub.1-zN (0<z<1). Thereby quaternary composition is adjusted for lattice match between the barrier layers and the well layers. Thus crystal defect caused by lattice mismatch is improved.

Claims

1. A nitride semiconductor structure comprising: a first type doped semiconductor layer; a light emitting layer, comprising a multiple quantum well (MQW) structure; an InGaN based second type hole supply layer; and a second type doped semiconductor layer, wherein the InGaN based second type hole supply layer is disposed between the second type doped semiconductor layer and the light emitting layer, and the light emitting layer is disposed between the InGaN based second type hole supply layer and the first type doped semiconductor layer, and the MQW structure comprises a plurality of barrier layers and a plurality of well layers stacked alternately, wherein the InGaN based second type hole supply layer is doped with a second type dopant at a concentration larger than 10.sup.18 cm.sup.3 and a Group IV-A element at a concentration large than 10.sup.17 cm.sup.3.

2. The nitride semiconductor structure as claimed in claim 1, wherein a material of each of the well layers comprises a GaN material containing indium.

3. The nitride semiconductor structure as claimed in claim 1, wherein a material of each of the barrier layers of the MQW structure comprises a GaN material containing indium and aluminum.

4. The nitride semiconductor structure as claimed in claim 1, wherein a material of each of the barrier layers of the MQW structure is doped with a first type dopant at a concentration ranging from 10.sup.16 cm.sup.3 to 10.sup.18 cm.sup.3.

5. The nitride semiconductor structure as claimed in claim 1, wherein thickness of each of the well layers of the MQW structure is ranging from 3.5 nm to 7 nm, and thickness of each of the barrier layers is ranging from 5 nm to 12 nm.

6. The nitride semiconductor structure as claimed in claim 1, wherein a band gap of the InGaN based second type hole supply layer is larger than a band gap of each of the well layers of the MQW structure.

7. The nitride semiconductor structure as claimed in claim 1, wherein the second type dopant in the InGaN based second type hole supply layer is magnesium, and the Group IV-A element is carbon.

8. The nitride semiconductor structure as claimed in claim 1, further comprising: an AlGaN based first type carrier blocking layer, disposed between the first type doped semiconductor layer and the light emitting layer.

9. The nitride semiconductor structure as claimed in claim 1, further comprising: an AlGaN based second type carrier blocking layer, disposed between the second type doped semiconductor layer and the light emitting layer.

10. A nitride semiconductor structure comprising: a first type doped semiconductor layer; a light emitting layer, comprising a multiple quantum well (MQW) structure; an InGaN based second type hole supply layer; a second type doped semiconductor layer, wherein the InGaN based second type hole supply layer is disposed between the second type doped semiconductor layer and the light emitting layer, and the light emitting layer is disposed between the InGaN based second type hole supply layer and the first type doped semiconductor layer, and the MQW structure comprises a plurality of barrier layers and a plurality of well layers stacked alternately; an AlGaN based first type carrier blocking layer, disposed between the second type doped semiconductor layer and the light emitting layer; and an AlGaN based second type carrier blocking layer, disposed between the second type doped semiconductor layer and the light emitting layer, wherein the InGaN based second type hole supply layer is doped with a second type dopant at a concentration larger than 10.sup.18 cm.sup.3 and a Group IV-A element at a concentration large than 10.sup.17 cm.sup.3.

11. The nitride semiconductor structure as claimed in claim 10, wherein a material of each of the well layers comprises a GaN material containing indium.

12. The nitride semiconductor structure as claimed in claim 10, wherein a material of each of the barrier layers of the MQW structure comprises a GaN material containing indium and aluminum.

13. The nitride semiconductor structure as claimed in claim 10, wherein a material of each of the bander layers of the MQW structure is doped with a first type dopant at a concentration is ranging from 10.sup.16 cm.sup.3 to 10.sup.18 cm.sup.3.

14. The nitride semiconductor structure as claimed in claim 10, wherein thickness of each of the well layers of the MQW structure is ranging from 3.5 nm to 7 nm, and thickness of each of the barrier layers is ranging from 5 nm to 12 nm.

15. The nitride semiconductor structure as claimed in claim 10, wherein a band gap of the InGaN based second type hole supply layer is larger than a band gap of each of the well layers of the MQW structure.

16. The nitride semiconductor structure as claimed in claim 10, wherein the second type dopant in the InGaN based second type hole supply layer is magnesium, and the Group IV-A element is carbon.

17. A nitride semiconductor structure comprising: a first type doped semiconductor layer; a light emitting layer, comprising a multiple quantum well (MQW) structure; an InGaN based second type hole supply layer; a second type doped semiconductor layer, wherein the InGaN based second type hole supply layer is disposed between the second type doped semiconductor layer and the light emitting layer, and the light emitting layer is disposed between the InGaN based second type hole supply layer and the first type doped semiconductor layer, and the MQW structure comprises a plurality of barrier layers and a plurality of well layers stacked alternately; and an AlGaN based first type carrier blocking layer, disposed between the second type doped semiconductor layer and the light emitting layer, wherein the InGaN based second type hole supply layer is doped with magnesium at a concentration larger than 10.sup.18 cm.sup.3 and carbon at a concentration large than 10.sup.17 cm.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein

[0013] FIG. 1 is a schematic drawing showing a cross section of an embodiment of a nitride semiconductor structure according to the present invention;

[0014] FIG. 2 is a schematic drawing showing a cross section of an embodiment of a semiconductor light emitting device including a nitride semiconductor structure according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] In the following embodiments, when it is mentioned that a layer of something or a structure is disposed over or under a substrate, another layer of something, or another structure, that means the two structures, the layers of something, the layer of something and the substrate, or the structure and the substrate can be directly or indirectly connected. The indirect connection means there is at least one intermediate layer disposed therebetween.

[0016] Referring to FIG. 1, a first type doped semiconductor layer 3 and a second type doped semiconductor layer 7 are disposed over a substrate 1. A light emitting layer 5 is disposed between the first type doped semiconductor layer 3 and the second type doped semiconductor layer 7. The light emitting layer 5 has a multiple quantum well (MQW) structure. The MQW structure includes a plurality of well layers 51 and barrier layers 52 stacked alternately. One well layer 51 is disposed between every two barrier layers 52. The barrier layer 52 is made of quaternary AlxInyGa1-x-yN (0<x<1, 0<y<1, 0<x+y<1) and the well layer 51 is made of material In.sub.zGa.sub.1-zN (0<z<1). The thickness of the well layer 51 is ranging from 3.5 nm to 7 nm, preferably from 4 nm to 5 nm. The thickness of the barrier layer 52 is ranging from 5 nm to 12 nm. The barrier layer 52 is doped with a first type dopant (such as silicon or germanium) at a concentration ranging from 10.sup.16 cm.sup.3 to 10.sup.18 cm.sup.3 so as to reduce carrier screening effect and increase carrier-confinement.

[0017] Moreover, a hole supply layer 8 is disposed between the light emitting layer 5 and the second type doped semiconductor layer 7. The hole supply layer 8 is made of In.sub.xGa.sub.1-xN (0<x<1) and is doped with a second type dopant (such as magnesium or zinc) at a concentration larger than 10.sup.18 cm.sup.3. The hole supply layer 8 is also doped with a Group IV A element whose concentration is ranging from 10.sup.17 cm.sup.3 to 10.sup.20 cm.sup.3. The optimal Group IV A element is carbon. The pentavalent nitrogen is replaced by carbon, so that the hole supply layer 8 has higher concentration of holes and more holes are provided to enter the light emitting layer 5. Thus the electron-hole recombination is increased. The band gap of the hole supply layer 8 is larger than that of the well layer 51 of MQW structure, so that the holes are allowed to enter the well layers and the electrons will not escape into the second type doped semiconductor layer 7.

[0018] Furthermore, a first type carrier blocking layer 4 made of material Al.sub.xGa.sub.1-xN (0<x<1) is disposed between the light emitting layer 5 and the first type doped semiconductor layer 3 while a second type carrier blocking layer 6 made of Al.sub.xGa.sub.1-xN (0<x<1) is disposed between the hole supply layer 8 and the second type doped semiconductor layer 7. Due to the property that the band gap of AlGaN containing aluminum is larger than that of the GaN, not only the range of band gap of the nitride semiconductor is increased, the carriers are confined in the MQW structure. Thus the electron-hole recombination rate is increased and the light emitting efficiency is improved.

[0019] In addition, a buffer layer 2 made of Al.sub.xGa.sub.1-xN (0<x<1) is disposed between the substrate 1 and the first type doped semiconductor layer 3. The buffer layer 2 is for improving lattice mismatch caused by the first type doped semiconductor layer 3 grown on the heterogeneous substrate 1. The materials for the buffer layer 2 can also be GaN, InGaN, SiC, ZnO, etc. The buffer layer is produced by a low-temperature epitaxial growth at the temperature ranging from 400 degrees Celsius ( C.) to 900 C.

[0020] While in use, the material for the substrate 1 can be sapphire, silicon, SiC, ZnO or GaN, etc. The first type doped semiconductor layer 3 is made of Si-doped or Ge-doped GaN-based materials while the second type doped semiconductor layer 7 is made of Mg-doped or Zn-doped GaN-based materials. The first type doped semiconductor layer 3 and the second type doped semiconductor layer 7 are produced by the method such as metalorganic chemical vapor deposition (MOCVD). As to the well layer 51 and the barrier layer 52, they are produced by metal organic chemical vapor deposition or molecular beam epitaxy (MBE) deposition of gas mixture of a lower alkyl group-indium and gallium compound. The barrier layers 52 are deposited at the temperature ranging from 850 C. to 1000 C. while the well layers 51 are formed at the temperature ranging from 500 C. to 950 C. The AlGaInN barrier layers 52 and the InGaN well layers 51 of the MQW structure have the same element-indium so that the lattice constant of the barrier layers 52 and the lattice constant of the well layers 51 are similar. Thus not only crystal defects caused by lattice mismatch between conventional InGaN well layers and GaN barrier layers can be improved, the stress caused by lattice constant mismatch between materials is also improved. The thickness of the well layer 51 of the nitride semiconductor structure is ranging from 3.5 nm to 7 nm, preferably from 4 nm to 5 nm.

[0021] Moreover, the piezoelectric field in the MQW structure is effectively reduced because that the quaternary AlGaInN barrier layers 52 and InGaN well layers 51 can improve the stress caused by lattice mismatch. Thus the tilted and twisted energy band is improved in a certain degree. Therefore the piezoelectric effect is reduced effectively and the internal quantum efficiency is increased.

[0022] The above nitride semiconductor structure is applied to semiconductor light emitting devices. Referring to FIG. 2, a cross section of a semiconductor light emitting device including the nitride semiconductor structure of an embodiment according to the present invention is revealed. The semiconductor light emitting device includes at least: a substrate 1, a first type doped semiconductor layer 3 disposed over the substrate 1 and made of Si-doped or Ge-doped GaN based materials, a light emitting layer 5 disposed over the first type doped semiconductor layer 3 and having a multiple quantum well (MQW) structure, a second type doped semiconductor layer 7 disposed over the light emitting layer 5 and made of Mg-doped or Zn-doped GaN based materials, a first type electrode 31 disposed on and in ohmic contact with the first type doped semiconductor layer 3, and a second type electrode 71 disposed on and in ohmic contact with the second type doped semiconductor layer 7.

[0023] The MQW structure includes a plurality of well layers 51 and barrier layers 52 stacked alternately. One well layer 51 is disposed between every two barrier layers 52. The barrier layer 52 is made of material Al.sub.xIn.sub.yGa.sub.1-x-yN and x and y satisfy the conditions: 0<x<1, 0<y<1, and 0<x+y<1 while the well layer 51 is made of material In.sub.zGa.sub.1-zN and 0<z<1. The thickness of the well layer 51 is ranging from 3.5 nm to 7 nm, preferably from 4 nm to 5 nm.

[0024] The first type electrode 31 and the second type electrode 71 are used together to provide electric power and are made of (but not limited to) the following materials: titanium, aluminum, gold, chromium, nickel, platinum, and their alloys. The manufacturing processes arc well-known to people skilled in the art.

[0025] Moreover, a first type carrier blocking layer 4 made of material Al.sub.xGa.sub.1-xN (0<x<1) is disposed between the light emitting layer 5 and the first type doped semiconductor layer 3 while a second type carrier blocking layer 6 made of material Al.sub.xGa.sub.1-xN (0<x<1) is disposed between the light emitting layer 5 and the second type doped semiconductor layer 7. Due to the property that the band gap of AlGaN containing aluminum is larger than that of GaN, not only the range of the band gap of the nitride semiconductor is increased, the carriers are also confined in the MQW structure. Thus the electron-hole recombination rate is increased and the light emitting efficiency is further improved.

[0026] A buffer layer 2 made of Al.sub.xGa.sub.1-xN (0<x<1) is disposed between the substrate 1 and the first type doped semiconductor layer 3 so as to improve lattice constant mismatch caused by the first type doped semiconductor layer 3 grown on the heterogeneous substrate 1. The buffer layer 2 can also be made of material including GaN, InGaN, SiC, ZnO, etc.

[0027] In summary, due to that both quaternary AlGaInN barrier layers 52 and ternary InGaN well layers 51 have the same element-indium, the quaternary composition of the semiconductor light emitting device of the present invention can be adjusted and improved for providing a lattice matching composition that allows the barrier layers 52 and the well layers 51 to have similar lattice constants. Thus not only crystal defects caused by lattice mismatch between conventional InGaN well layers and GaN barrier layers can be improved, the stress caused by lattice mismatch is also improved. The thickness of the well layer 51 of the nitride semiconductor structure is ranging from 5 nm to 7 nm, preferably from 4 nm to 5 nm. Moreover, the addition of more aluminum (Al) in the harrier layer 52 provides a better carrier confinement and electrons and holes are effectively confined in the well layer 51. Thereby the internal quantum efficiency is increased and the semiconductor light emitting device provides a better light emitting efficiency.

[0028] Furthermore, the quaternary AlGaInN barrier layers and the ternary InGaN well layers can improve the stress caused by lattice mismatch and further reduce the piezoelectric field in the MQW structure effectively. Thus the piezoelectric effect is inhibited and the internal quantum efficiency is improved. Therefore, the semiconductor light emitting device gets a better light emitting efficiency.

[0029] Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.