Enhancement of optical polarization of nitride light-emitting diodes by wafer off-axis cut

• US 8,278,128 B2
• Filed: 02/02/2009
• Issued: 10/02/2012
• Est. Priority Date: 02/01/2008
• Status: Expired due to Fees

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Masui, Hisashi, Yamada, Hisashi, Iso, Kenji, Hirai, Asako, Saito, Makoto, Speck, James S., Nakamura, Shuji, DenBaars, Steven P.
• Primary Examiner(s): AU, BAC H
• Application Number:
  US12/364,272
• Publication Number:
  US 20100052008A1
• Time in Patent Office: 1,338 Days
• Field of Search: 438/29, 438/46, 438/47, 438/93, 438/150, 438/285, 438/483, 438/503, 438/590, 438/604, 438/796
• US Class Current: 438/46
• CPC Class Codes: H01L 33/16 with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

An off-axis cut of a nonpolar III-nitride wafer towards a polar (−c) orientation results in higher polarization ratios for light emission than wafers without such off-axis cuts. A 5° angle for an off-axis cut has been confirmed to provide the highest polarization ratio (0.9) than any other examined angles for off-axis cuts between 0° and 27°.

Claims

1. A method of fabricating a light-emitting diode (LED), comprising:

growing an LED structure on or above a surface of a nonpolar III-nitride substrate, wherein;

the surface is at an angle with respect to a nonpolar plane of the nonpolar III-nitride substrate,

the angle is towards a polar (−

c or +c) orientation, and

the surface obtains a pre-determined polarization ratio of light emitted by the LED structure.

2. The method of claim 1, wherein the angle is such that light emission from the LED has a higher polarization ratio than an LED grown on the nonpolar plane of the nonpolar III-nitride substrate.

3. The method of claim 1, wherein the angle is between 0°

and 27° and

towards the [000-1] orientation.

4. The method of claim 1, wherein the angle is about 5°

.

5. The method of claim 1, wherein the angle and the LED structure obtain a polarization ratio of at least 0.91 for light emitted by the LED structure having a wavelength of 450 nm.

6. The method of claim 1, wherein the angle and the LED structure obtain a polarization ratio that exceeds 0.8 for light emitted by the LED structure having a wavelength of 430 nm.

7. The method of claim 1, wherein the angle and the LED structure obtain a polarization ratio that exceeds 0.8 for light emitted by the LED structure having a wavelength of 470 nm.

8. The method of claim 1, wherein the angle and the LED structure obtain a polarization ratio of at least about 0.55 for light emitted by the LED structure having a wavelength of 450 nm.

9. The method of claim 1, wherein the angle and the LED structure obtain a polarization ratio of at least about 0.55 for light emitted by the LED having a wavelength of 390 nm.

10. The method of claim 1, wherein the LED structure is a nonpolar LED structure.

11. A light-emitting diode (LED) fabricated according to the method of claim 1.

12. The method of claim 1, further comprising selecting the angle to control a polarization ratio of light emitted by the LED structure.

13. The method of claim 1, wherein the surface obtains a polarization ratio in excess of 0.9 for one or more selected wavelengths of light emitted by the LED structure.

14. The method of claim 1, wherein the surface maximizes a polarization ratio of light emitted by the LED structure.

15. The method of claim 1, further comprising selecting the surface to obtain the pre-determined polarization ratio of light emitted by the LED structure.

16. The method of claim 1, further comprising selecting the surface depending on a wavelength and polarization ratio of light emitted by the LED.

17. The method of claim 1, wherein the surface obtains the LED structure emitting polarized light for back lighting a liquid crystal display.

18. The method of claim 1, wherein the LED is a backlight for a liquid crystal display, wherein the liquid crystal display does not comprise a polarizer.

19. The method of claim 1, wherein the III-nitride substrate is a Gallium Nitride substrate.

20. The method of claim 19, wherein the non-polar surface orientation of the Gallium Nitride substrate is m-plane.

21. The method of claim 1, wherein the surface is an off-axis cut or miscut of the III-nitride substrate.

22. The method of claim 1, wherein the surface is a semipolar plane and the LED structure is a semipolar LED structure.

23. The method of claim 1, further comprising providing or obtaining the surface of the III-nitride substrate, or miscutting the III-nitride substrate to form the surface.

24. A method of fabricating a light-emitting diode (LED), comprising:

providing or obtaining a surface of a III-nitride substrate, or miscutting the III-nitride substrate to form the surface, wherein;

the surface is at an angle with respect to a nonpolar plane of the III-nitride substrate, and

the angle is towards a polar (−

c or +c) orientation, and

growing an LED structure on or above the surface of a III-nitride substrate, wherein the angle is selected to control a polarization ratio of light emitted by the LED structure.

25. The method of claim 24, wherein the surface obtains the LED structure emitting polarized light for back lighting a liquid crystal display.

26. The method of claim 24, wherein the surface obtains a polarization ratio in excess of 0.9 for one or more selected wavelengths of light emitted by the LED structure.