Gallium nitride-based compound semiconductor multilayer structure and production method thereof
The object of the present invention is to provide a gallium nitride-based compound semiconductor multilayer structure useful for manufacturing a gallium nitride-based compound semiconductor light-emitting device which requires a low operating voltage and from which a good emission output can be obtained. The present gallium nitride-based compound semiconductor multilayer structure comprises a substrate having thereon an n-type layer, a light-emitting layer and a p-type layer, the light-emitting layer having a multiple quantum well structure in which a well layer and a barrier layer are alternately stacked repeatedly and the light-emitting layer being provided between the n-type layer and the p-type layer, wherein the well layers consisting of the multiple quantum well structure comprise a well layer having an ununiform thickness and a well layer having a uniform thickness.
1. A gallium nitride-based compound semiconductor multilayer structure comprising a substrate having thereon a n-type layer, a light-emitting layer and a p-type layer, the light-emitting layer having a multiple quantum well structure in which a well layer and a barrier layer are alternately stacked repeatedly and the light-emitting layer being provided between the n-type layer and the p-type layer, wherein the well layers constituting the multiple quantum well structure comprise a well layer having an ununiform thickness and a well layer having a uniform thickness.
2. The gallium nitride-based compound semiconductor multilayer structure according to claim 1 , wherein the thickness of the well layer closest to the p-type layer is uniform.
3. The gallium nitride-based compound semiconductor multilayer structure according to claim 1 , wherein the thickness of the well layer closest to the n-type layer is uniform.
4. The gallium nitride-based compound semiconductor multilayer structure according to claim 1 , wherein the thickness of a well layer having a uniform thickness is 1.8 to 5 nm.
5. The gallium nitride-based compound semiconductor multilayer structure according to claim 1 , wherein the thickness of a thin part of a well layer having an ununiform thickness is not more than 2.7 nm
6. The gallium nitride-based compound semiconductor multilayer structure according to claim 1 , wherein the multiple quantum well structure comprises 3 to 10 stacks of the well layer and the barrier layer.
7. The gallium nitride-based compound semiconductor multilayer structure according to claim 1 , wherein the barrier layer comprises a gallium nitride-based compound semiconductor selected from the group consisting of GaN, AlGaN and InGaN having a In ratio smaller than that of InGaN which forms the well layer.
8. The gallium nitride-based compound semiconductor multilayer structure according to claim 7 , wherein the barrier layer comprises GaN.
9. The gallium nitride-based compound semiconductor multilayer structure according to claim 1 , wherein the barrier layer contains a dopant.
10. The gallium nitride-based compound semiconductor multilayer structure according to claim 9 , wherein the dopant is at least one selected from the group consisting of C, Si, Ge, Sn, Pb, O, S, Se, Te, Po, Be, Mg, Ca, Sr, Ba and Ra.
11. The gallium nitride-based compound semiconductor multilayer structure according to claim 9 , wherein the concentration of the dopant is from 1×10 17 to 1×10 18 cm −3 .
12. The gallium nitride-based compound semiconductor multilayer structure according to claim 1 , wherein the thickness of the barrier layer is from 7 to 50 nm.
13. The gallium nitride-based compound semiconductor multilayer structure according to claim 12 , wherein the thickness of the barrier layer is at least 14 nm.
14. The gallium nitride-based compound semiconductor multilayer structure according to claim 1 , wherein the well layer contains In.
15. The gallium nitride-based compound semiconductor multilayer structure according to claim 14 , wherein a thin layer containing no In is provided on at least the substrate side of the barrier layer.
16. A gallium nitride-based compound semiconductor light-emitting device, wherein the device has a negative electrode and a positive electrode, the negative electrode and the positive electrode being provided on the n-type layer and the p-type layer of a gallium nitride-based compound semiconductor multilayer structure according to claim 1 .
17. A lamp in which the gallium nitride-based compound semiconductor light-emitting device according to claim 16 is used.
18. A method for manufacturing the gallium nitride-based compound semiconductor multilayer structure according to claim 1 , wherein after a well layer is formed, the layer thus formed is partly decomposed or sublimated to provide an ununiform thickness.
19. The method for manufacturing a gallium nitride-based compound semiconductor multilayer structure, according to claim 18 , wherein the substrate temperature T 1 during forming the well layer and the substrate temperature T 2 during decomposing or sublimating a part of the well layer satisfy the formula: T 1 ≦T 2 .
20. The method for manufacturing a gallium nitride-based compound semiconductor multilayer structure, according to claim 18 , wherein the decomposition or sublimation of a part of the well layer is conducted in an atmosphere containing a nitrogen source and containing no III group metal source.
21. The method for manufacturing a gallium nitride-based compound semiconductor multilayer structure, according to claim 18 , wherein the decomposition or sublimation of a part of the well layer is conducted during forming the barrier layer.