Enhancement of optical polarization of nitride light-emitting diodes by increased indium incorporation

• US 8,044,417 B2
• Filed: 02/02/2009
• Issued: 10/25/2011
• Est. Priority Date: 02/01/2008
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Iso, Kenji, Speck, James S., DenBaars, Steven P., Nakamura, Shuji, Masui, Hisashi, Yamada, Hisashi
• Primary Examiner(s): NGO, NGAN V
• Application Number:
  US12/364,258
• Publication Number:
  US 20090194761A1
• Time in Patent Office: 995 Days
• Field of Search: 257/96, 257/97, 257/103, 257/E33.023, 257/E33.025, 257/E33.028
• US Class Current: 257/96
• CPC Class Codes: H01L 33/16 with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous
• CPC Class Codes: H01L 33/34 containing only elements of Group IV of the Periodic Table

Abstract

An increase in the Indium (In) content in light-emitting layers of light-emitting diode (LED) structures prepared on nonpolar III-nitride substrates result in higher polarization ratios for light emission than LED structures containing lesser In content. Polarization ratios should be higher than 0.7 at wavelengths longer than 470 nm.

Claims

1. A light-emitting diode (LED) that emits polarized light comprising:

one or more III-nitride light-emitting layers formed on a III-nitride layer, wherein the III-nitride light-emitting layers have an Indium (In) content that increases a polarization ratio of light emitted by the III-nitride light-emitting layers to greater than 0.8.

2. The LED of claim 1, wherein the In content increases a strain in the III-nitride light-emitting layers due to an increased lattice mismatch with the III-nitride layer, in order to increase the polarization ratio above 0.8.

3. The LED of claim 1, wherein the III-nitride light-emitting layers comprise one or more (Al_zIn_yGa_x)N (where 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1) semiconductors.

4. The LED of claim 3, wherein the (Al_zIn_yGa_x)N semiconductors are prepared epitaxially on a nonpolar orientation of a wurtzite crystal.

5. The LED of claim 3, wherein the (Al_zIn_yGa_x)N semiconductors are prepared epitaxially on a GaN substrate or GaN template.

6. The LED of claim 5, wherein the GaN template is a GaN layer prepared on a foreign substrate.

7. The LED of claim 3, wherein the (Al_zIn_yGa_x)N semiconductors are prepared on an (Al_zIn_yGa_x)N substrate or template which is not GaN, with 0≦

x<

1, 0≦

y≦

1, 0≦

z≦

1, and x+y+z=1, to set a platform for strain management different from that of GaN.

8. The LED of claim 1, wherein the III-nitride light-emitting layers comprise a quantum-well (QW) structure or double-hetero (DH) structure, and wherein the QW or DH structure includes a light-emitting active layer embedded between one or more barrier layers or cladding layers that have a larger band gap than a band gap of the active layer.

9. The LED of claim 8, wherein the active layer comprises (In_yGa_x)N (where 0≦

x≦

1, 0<

y≦

1, and x+y=1) embedded between one or more In_yGaN or GaN layers that have smaller In content (y) value than a y value of the active layer.

10. The LED of claim 8, wherein the active layer is a single QW structure or a multiple QW structure.

11. The LED of claim 8, wherein the active layer comprises In_yGaN with an Indium (In) content y in a range 0<

y≦

1, the In content controls induced strain in the active layer, and the induced strain controls a degree of polarization of the polarized light.

12. The LED of claim 8, wherein the active layer is thinner than a critical thickness to avoid generation of misfit dislocations that release strain.

13. The LED of claim 8, wherein the active layer is A1InGaN to adjust strain.

14. A method of fabricating a Light-Emitting Diode (LED), comprising;

controlling a degree of polarization of light emitted from the LED by forming one or more III-nitride light-emitting layers on a III-nitride layer, wherein the III-nitride light-emitting layers have an Indium (In) content that increases a polarization ratio of light emitted by the III-nitride light-emitting layers to greater than 0.8.

15. The method of claim 14, wherein the controlling step comprises changing the Indium (In) content in the III-nitride light-emitting layers to control induced strain.

16. The method of claim 15, wherein

the III-nitride light-emitting layers comprises (In_yGa_x)N (where 0≦

x≦

1, 0<

y≦

1, and x+y=1) embedded between one or more In_yGaN or GaN barrier layers, and

the controlling step comprises changing the In content (y,0<

y≦

1) in the III-nitride light-emitting layers to control the induced strain, while In content of the barrier layers is unchanged.

17. The method of claim 16, further comprising changing an Aluminum (Al) content of the III-nitride light-emitting layers to A1InGaN to adjust strain while an Al content of the barrier layers is unchanged.

18. The method of claim 14, wherein the controlling step comprises increasing the degree of polarization by increasing the Indium (In) content in one or more of the III-nitride light-emitting layers.

19. The method of claim 18, wherein the increased In content increases a strain in the III-nitride light-emitting layers due to an increased lattice mismatch with the III-nitride layer, in order to increase the polarization ratio.

20. A method for emitting light from a light-emitting diode (LED), comprising:

emitting polarized light from one or more III-nitride light-emitting layers formed on a III-nitride layer of the LED, wherein the III-nitride light-emitting layers have an Indium (In) content that increases a polarization ratio of the light emitted by the III-nitride light-emitting layers to greater than 0.8.