Laser diode and method for fabricating same
A laser diode and method for fabricating same, wherein the laser diode generally comprises an InGaN compliance layer on a GaN n-type contact layer and an AlGaN/GaN n-type strained super lattice (SLS) on the compliance layer. An n-type GaN separate confinement heterostructure (SCH) is on said n-type SLS and an InGaN multiple quantum well (MQW) active region is on the n-type SCH. A GaN p-type SCH on the MQW active region, an AlGaN/GaN p-type SLS is on the p-type SCH, and a p-type GaN contact layer is on the p-type SLS. The compliance layer has an In percentage that reduces strain between the n-type contact layer and the n-type SLS compared to a laser diode without the compliance layer. Accordingly, the n-type SLS can be grown with an increased Al percentage to increase the index of refraction. This along with other features allows for reduced threshold current and voltage operation.
1. A method for fabricating a Group-III nitride laser diode, comprising:
growing an n-type contact layer on a substrate at a temperature within a first growth temperature range;
growing an n-type compliance layer on said n-type contact layer at a temperature within a second growth temperature range that is lower than said first growth temperature;
growing a cap layer on said compliance layer at a temperature in said second temperature range to protect said compliance layer from temperatures in said first temperature range used to grow subsequent layers;
growing an n-type waveguiding element and on said cap layer at a temperature within said first growth temperature range, said waveguiding element grown with a higher index of refraction compared to laser diodes without said compliance layer;
growing an n-type separate confinement heterostructure (SCH) on said n-type waveguiding element;
growing an active region on said n-type SCH;
growing an undoped layer adjacent said active region on said n-type SCH;
growing a p-type SCH on said active region; and
growing a p-type waveguiding element on said p-type SCH.
2. The method of claim 1 , wherein said active region comprises multiple quantum wells.
3. The method of claim 2 , wherein said active region comprises three quantum wells.
4. The method of claim 1 , further comprising growing a p-type contact layer on said p-type SLS at a temperature within said first temperature range.
5. A method for fabricating a Group-III nitride laser diode, comprising:
growing an n-type contact layer on a substrate at a temperature within a first growth temperature range;
growing an n-type compliance layer on said n-type contact layer at a temperature within a second growth temperature range that is lower than said first growth temperature;
growing a cap layer on said compliance layer at a temperature in said second temperature range to protect said compliance layer from temperatures in said first temperature range used to grow subsequent layers;
growing an n-type waveguiding element and on said cap layer at a temperature within said first growth temperature range, said waveguiding element grown with a higher index of refraction compared to laser diodes without said compliance layer;
growing an n-type separate confinement heterostructure (SCH) on said n-type waveguiding element;
growing an active region on said n-type SCH;
growing a p-type SCH on said active region; and
growing a p-type waveguiding element on said p-type SCH, wherein said n-type SCH, active region and p-type waveguiding element are grown at a temperature within said second growth temperature range, and said p-type SCH is grown at a temperature within said first temperature range.
6. The method of claim 1 , wherein said first temperature range is from 1000 to 1100° C.
7. The method of claim 1 , wherein said second temperature range is from 700 to 1000° C.
8. The method of claim 1 , wherein said n-type contact layer comprises GaN grown at a rate in the range of 1.5 to 3 μm/hr and with a silicon doping density in the range of 1E17 to 1E19 cm −3 .
9. The method of claim 1 , wherein said compliance layer comprises In x Ga 1-x N wherein x is in the range of 0 to 0.20 and the Si doping density is in the range of 1E17 to 1E19 cm −3 .
10. The method of claim 1 , wherein said n-type waveguiding element comprises an n-type Al x Ga 1-x N/GaN strained layer superlattice (SLS).
11. The method of claim 10 , wherein said n-type Al x Ga 1-x N/GaN SLS has x in the range of 0.1 to 0.3 and wherein said GaN layers have a Si doping density in the range of 1E17 to 1E19 cm −3 .
12. The method of claim 1 , wherein said n-type SCH comprises GaN grown at a rate in the range of 0.5 to 2 A/s with a Si doping density in the range of 1E17 to 1E18 cm −3 .
13. The method of claim 1 , wherein said n-type SCH has a thickness in the range of 0.07 to 0.15 μm.
14. The method of claim 1 , wherein said active region comprises an In x Ga 1-x N/In y Ga 1-y N multiple quantum well stack with x in the range of 0.8 to 0.12, and y in the range of 0 to 0.04, and a growth rate in the range of 0.3 to 0.6 A/s.
15. The method of claim 1 , wherein said active region comprises three quantum wells with surrounding barrier layers, the width of each said quantum well in the range of 3-5 nm, and each barrier layer width in the range of 4-8 nm.
16. The method of claim 1 , wherein said p-type SCH comprises GaN grown at a rate in the range of 1-2 A/s with a Mg doping density of 1E18 to 5E19 cm-3 and a thickness in the range of 0.07 to 0.15 μm.
17. The method of claim 1 , wherein said p-type waveguiding element comprises a p-type Al x Ga 1-x N/GaN strained layer superlattice (SLS) with x in the range of 0.1 to 0.3 and said GaN is Mg doped at a density in the range of 8E18 to 5E19 cm −3 .
18. The method of claim 17 , wherein the growth rate of said p-type SLS is in the range of 0.5 to 1 A/s.
19. The method of claim 4 , wherein said p-type contact layer comprises p-type GaN doped with a Mg doping density in the range of 1E19 to 5E20 cm −3 , grown at a rate in the range of 0.5 to 2 A/s to a thickness in the range of 20 to 50 nm.
20. The method of claim 4 , wherein said p-type contact layer is grown with a ramp-up in doping density.
21. The method of claim 4 , wherein said p-type contact layer is grown with a ramp-up in doping density.
22. The method of claim 1 , further comprising growing a p-type electron blocking layer on said active region at prior to growing said p-type SCH.
23. The method of claim 22 , wherein said blocking layer comprises p-type Al x Ga 1-x N, where x is in the range of 0.15 to 0.25, having an Mg doping in the range of 7E18 to 3E19 cm −3 and a thickness in the range of 15-25 nm.
24. A method for fabricating a Group-III nitride laser diode, comprising:
growing an n-type contact layer on a substrate at a temperature within a first growth temperature range;
growing an n-type compliance layer on said n-type contact layer at a temperature within a second growth temperature range that is lower than said first growth temperature;
growing a cap layer on said compliance layer at a temperature in said second temperature range to protect said compliance layer from temperatures in said first temperature range used to grow subsequent layers;
growing an n-type waveguiding element and on said cap layer at a temperature within said first growth temperature range, said waveguiding element grown with a higher index of refraction compared to laser diodes without said compliance layer;
growing an n-type separate confinement heterostructure (SCH) on said n-type waveguiding element;
growing an active region on said n-type SCH;
growing a p-type SCH on said active region;
growing a p-type waveguiding element on said p-type SCH; and
growing a p-type electron blocking layer on said active region at prior to growing said p-type SCH, wherein the first 1-10 nm of said blocking layer is grown at a temperature within said second growth temperature range, and the remaining of said blocking layer is grown at a temperature within said first growth temperature range.