Group-III nitride semiconductor device
An object of the present invention is to provide a Group III nitride semiconductor element which comprises a thick AlGaN layer exhibiting high crystallinity and containing no cracks, and which does not include a thick GaN layer (which generally serves as a light-absorbing layer in an ultraviolet LED). The inventive Group III nitride semiconductor element comprises a substrate; a first nitride semiconductor layer composed of AlN which is provided on the substrate; a second nitride semiconductor layer composed of Al x1 Ga 1-x1 N (0≦x1≦0.1) which is provided on the first nitride semiconductor layer; and a third nitride semiconductor layer composed of Al x2 Ga 1-x2 N (0<x2<1 and x1+0.02≦x2) which is provided on the second nitride semiconductor layer.
1. A Group III nitride semiconductor element comprising
a substrate;
a first nitride semiconductor layer composed of AlN single crystal having a thickness of 0.005 to 0.5 μm which is provided on the substrate;
a second nitride semiconductor layer composed of Al x1 Ga 1-x1 N(0<x1≦0.05) which is provided on the first nitride semiconductor layer;
a third nitride semiconductor layer composed of Al x2 Ga 1-x2 N(x1+0.02≦x2≦0.5) which is provided on the second nitride semiconductor layer; and
a fourth nitride semiconductor layer which is provided on the third nitride semiconductor layer, the fourth nitride semiconductor layer including:
an n-type contact layer composed of Al a Ga 1-a N (0<a<1),
an n-type cladding layer composed of Al b Ga 1-b N (0<b<0.4) which is provided on the n-type contact layer, and
a light-emitting layer which has a multiple quantum well (MQW) structure including a well layer composed of Ga 1-s In s N (0<s<0.1) and a barrier layer composed of Al c Ga 1-c N c (0≦c<0.3 and c<b) doped with Si, and is provided on the n-type cladding layer.
2. A Group III nitride semiconductor element according to claim 1 , wherein said substrate is selected from a group consisting of sapphire single crystal, Si single crystal, SiC single crystal, AlN single crystal, and GaN single crystal.
3. A Group III nitride semiconductor element according to claim 1 , wherein said second nitride semiconductor layer is formed of an island-like structure in which crystals of different heights are arranged so as to be separated from one another.
4. A Group III nitride semiconductor element according to claim 3 , wherein the Al content of said second nitride semiconductor layer differs from region to region of the island-like structure.
5. A Group III nitride semiconductor element according to claim 4 , wherein the second nitride semiconductor layer has a region having a lower Al content at a position closer to the substrate and a higher Al content at a position farther from the substrate.
6. A Group III nitride semiconductor element according to claim 1 , wherein said second nitride semiconductor layer is composed of Al x1 Ga 1-x1 N(0<x1≦0.02).
7. A Group III nitride semiconductor element according to claim 1 , wherein said second nitride semiconductor layer has a thickness of 1 to 500 nm.
8. A Group III nitride semiconductor element according to claim 7 , wherein said second nitride semiconductor layer has a thickness of 1 to 400 nm.
9. A Group III nitride semiconductor element according to claim 8 , wherein said second nitride semiconductor layer has a thickness of 1 to 300 nm.
10. A Group III nitride semiconductor element according to claim 1 , wherein said second nitride semiconductor layer is composed of an undoped semiconductor.
11. A Group III nitride semiconductor light-emitting device comprising a Group III nitride semiconductor element according to claim 1 , wherein:
the fourth nitride semiconductor layer further includes a p-type layer provided on said a light-emitting layer,
a negative electrode provided on said n-type contact layer; and
a positive electrode provided on said p-type layer.
12. A light-emitting diode comprising a Group III nitride semiconductor light-emitting device according to claim 11 .
13. A laser diode comprising a Group III nitride semiconductor light-emitting device according to claim 11 .
14. A semiconductor device comprising a Group III nitride semiconductor element according to claim 1 .