Gallium nitride-based compound semiconductor multilayer structure and production method thereof
An object of the present invention is to provide a gallium nitride compound semiconductor multilayer structure useful for producing a gallium nitride compound semiconductor light-emitting device which operates at low voltage while maintaining satisfactory light emission output. The inventive gallium nitride compound semiconductor multilayer structure comprises a substrate, and an n-type layer, a light-emitting layer, and a p-type layer formed on the substrate, the light-emitting layer having a multiple quantum well structure in which a well layer and a barrier layer are alternately stacked repeatedly, said light-emitting layer being sandwiched by the n-type layer and the p-type layer, wherein the well layer comprises a thick portion and a thin portion, and the barrier layer contains a dopant.
1. A method for producing a gallium nitride compound semiconductor multilayer structure comprising a substrate, and an n-type layer, a light-emitting layer, and a p-type layer formed on the substrate, the light-emitting layer having a multiple quantum well structure in which a well layer and a barrier layer are alternately stacked repeatedly, said light-emitting layer being sandwiched by the n-type layer and the p-type layer, the gallium nitride compound semiconductor multilayer structure being a light-emitting device emitting blue light or green light, wherein the method comprises forming a thick portion and a thin portion in the well layer by doping the barrier layer with a dopant.
2. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 1 , wherein the dopant is contained at a concentration of 1×10 17 cm −3 to 1×10 19 cm −3 .
3. A method for producing a gallium nitride compound semiconductor multilayer structure comprising a substrate, and an n-type layer, a light-emitting layer, and a p-type layer formed on the substrate, the light-emitting layer having a multiple quantum well structure in which a well layer and a barrier layer are alternately stacked repeatedly, the light-emitting layer being sandwiched between the n-type layer and the p-type layer, wherein the well layer comprises a thick portion and a thin portion, and the barrier layer contains a dopant, wherein the method comprises a step of forming the well layer, which step includes a step of growing a gallium nitride compound semiconductor and a step of decomposing or sublimating a portion of the gallium nitride compound semiconductor.
4. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 3 , wherein the step of growing is performed at a substrate temperature of T 1 and the step of decomposing or sublimating is performed at a substrate temperature of T 2 , wherein T 1 and T 2 satisfy the relationship: T 1 ≦T 2 .
5. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 4 , wherein T 1 falls within a range of 650 to 900° C.
6. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 5 , wherein T 2 falls within a range of 700 to 1,000° C.
7. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 4 , wherein the step of decomposing or sublimating is performed while the substrate temperature T 1 is elevated to T 2 .
8. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 7 , wherein the substrate temperature T 1 is elevated to T 2 at a temperature elevation rate of 1° C./min to 100° C./min.
9. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 8 above, wherein the temperature elevation rate is 5° C./min to 50° C./min.
10. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 7 , wherein the substrate temperature T 1 is elevated to T 2 over 30 seconds to 10 minutes.
11. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 10 , wherein the substrate temperature T 1 is elevated to T 2 over one minute to five minutes.
12. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 4 , wherein the barrier layer is grown at T 2 .
13. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 12 , wherein the barrier is grown at T 2 , followed by lowering the substrate temperature to T 3 at which further growth is performed.
14. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 13 , wherein T 3 is equal to T 1 .
15. A method for producing a gallium nitride compound semiconductor multilayer structure according to claim 3 , wherein the step of growing is performed in an atmosphere containing a nitrogen source and a Group III metal source and the step of decomposing or sublimating is performed in an atmosphere containing a nitrogen source but no Group III metal source.