ENHANCEMENT OF OPTICAL POLARIZATION OF NITRIDE LIGHT-EMITTING DIODES BY INCREASED INDIUM INCORPORATION

• US 20090194761A1
• Filed: 02/02/2009
• Published: 08/06/2009
• 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: Speck, James S., DenBaars, Steven P., Nakamura, Shuji, Masui, Hisashi, Yamada, Hisashi, Iso, Kenji
• Granted Patent: US 8,044,417 B2
• Time in Patent Office: Days
• US Class Current: 257/13
• 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.

4. The LED of claim 1, comprising one or more (Al_zIn_yGa_x)N (where 0≦

x≦

1, 0≦

y≦

1, 0≦

z≦

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

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

6. The LED of claim 4, wherein the (Al_zIn_yGa_x)N semiconductors are prepared epitaxially on a GaN substrate or GaN template.

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

8. The LED of claim 4, 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.

9. The LED of claim 1, comprising a quantum-well (QW) structure or double-hetero (DH) structure, 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.

10. The LED of claim 9, 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.

11. The LED of claim 9, wherein the active layer is a single QW structure or a multiple QW structure.

12. The LED of claim 9, 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.

13. The LED of claim 9, wherein the active layer is thinner than a critical thickness to avoid generation of misfit dislocations that release strain.

14. The LED of claim 9, wherein the active layer is AlInGaN to adjust strain.

2. The LED of claim 2, comprising one or more light-emitting layers, wherein an Indium (In) content of the light-emitting layers is such that a polarization ratio of the polarized light emitted by the light-emitting layers is greater than 0.8.

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

15. A method of fabricating a Light-Emitting Diode (LED), comprising controlling a degree of polarization of light emitted from the LED.

16. The method of claim 15, wherein the controlling is changing an Indium (In) content in the active layer to control induced strain.

17. The method of claim 16, wherein

(1) the LED comprises an active layer,

(2) 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 barrier layers, and

(3) the controlling comprises changing the In content (y, 0<

y≦

1) in the active layer to control the induced strain, while In content of the barrier layers is unchanged.

18. The method of claim 17, further comprising changing an Aluminum (Al) content of the active layer to AlInGaN to adjust strain while an Al content of the barrier layers is unchanged.

19. The method of claim 15, wherein the controlling is increasing the degree of polarization by increasing an Indium (In) content in one or more light-emitting layers of the LED.

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

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

emitting light from a light-emitting region of the LED, wherein an Indium content of the light-emitting region is such that a polarization ratio of the light is greater than 0.8.