Optical device structure using miscut GaN substrates for laser applications
An optical device capable of emitting light having a wavelength ranging from about 490 to about 580 nanometers has a gallium nitride substrate with a semipolar crystalline surface region characterized by an orientation of greater than 3 degrees from (11-22) towards (0001) but less than about 50 degrees. A laser stripe formed on the substrate has a cavity orientation substantially parallel to the m-direction.
1. A semiconductor laser comprising:
a gallium nitride substrate having a semipolar crystalline surface region characterized by and an orientation of greater than about 2 degrees from an (11-22) plane toward a (0001) plane, but less than about 50 degrees, and having an m-direction, and a c-projection direction perpendicular to the m-direction;
a laser region formed over the semipolar crystalline surface region, the laser region having a cavity orientation substantially parallel to the m-direction and extending from a first end to a second end, and having an indium concentration sufficient to cause emission of polarized light of about at least 490 nm wavelength;
a first cleaved m-face facet on the first end; and
a second cleaved m-face facet on the second end;
wherein the laser region emits light polarized substantially parallel to the c-projection direction.
2. The semiconductor laser of claim 1 wherein the first cleaved m-face facet is substantially parallel to the second cleaved m-face facet.
3. The semiconductor laser of claim 2 further comprising a reflective coating over each of the first cleaved m-face facet and the second cleaved m-face facet.
4. The semiconductor laser of claim 3 wherein the reflective coating is selected from silicon dioxide, hafnia, titania, tantalum pentoxide, zirconia, and a combination of any of the foregoing.
5. The semiconductor laser of claim 1 wherein the laser region has a length between about 50 microns and about 3000 microns.
6. The semiconductor laser of claim 1 wherein the laser region has a width between about 0.5 microns and about 50 microns.
7. The semiconductor laser of claim 1 wherein the light polarized substantially parallel to the c-projection direction has a polarization ratio greater than about 0.2 and less than about 1 in the c-projection direction.
8. The semiconductor laser of claim 1 wherein the light polarized substantially parallel to the c-projection direction has a wavelength between about 490 nanometers and about 580 nanometers.
9. The semiconductor laser of claim 1 further comprising an n-type metal contact to a back of the gallium nitride substrate and a p-type metal contact to an upper portion of the laser region.
10. The semiconductor laser of claim 9 wherein the laser region further comprises a dielectric layer over the laser region with an opening for the p-type metal contact to the upper portion of the laser region.
11. The semiconductor laser of claim 1 wherein the laser region comprises
an n-type gallium nitride region on the semipolar crystalline surface region;
an active region over the n-type gallium nitride region; and
a laser stripe region over the active region.
12. The semiconductor laser of claim 11 wherein the active region includes between one and twenty quantum well regions.
13. The semiconductor laser of claim 12 wherein the active region includes an electron blocking region.
14. The semiconductor laser of claim 13 wherein the active region comprises a separate confinement heterostructure.
15. The semiconductor laser of claim 1 wherein the orientation of the semipolar crystalline surface region is approximately (11-23).
16. The semiconductor laser of claim 1 wherein the orientation of the semipolar crystalline surface region is approximately (11-24).
17. The semiconductor laser of claim 1 , wherein the semipolar crystalline surface region comprises a surface dislocation density below about 10 5 cm −2 .
18. A semiconductor laser comprising:
a gallium nitride substrate having a semipolar crystalline surface region characterized by an orientation of approximately (11-23) and having an m-direction, and a c-projection direction perpendicular to the m-direction;
a laser region formed over the semipolar crystalline surface region, the laser region having a cavity orientation substantially parallel to the m-direction and extending from a first end to a second end, and having an indium concentration sufficient to cause emission of polarized light of about at least 490 nm wavelength;
a first cleaved m-face facet on the first end; and
a second cleaved m-face facet on the second end;
wherein the laser region emits light polarized substantially parallel to the c-projection direction.