Optical devices featuring textured semiconductor layers

• US 20070120141A1
• Filed: 10/31/2006
• Published: 05/31/2007
• Est. Priority Date: 04/15/2004
• Status: Active Grant

• Current Assignee: Trustees of Boston University
• Original Assignee: Trustees of Boston University
• Inventors: Moustakas, Theodore, Cabalu, Jasper
• Granted Patent: US 8,035,113 B2
• Time in Patent Office: Days
• US Class Current: 257/103
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01L 29/155 Comprising only semiconductor materials H01L29/154 takes precedence
• CPC Class Codes: H01L 29/2003 Nitride compounds
• CPC Class Codes: H01L 31/0236 Special surface textures
• CPC Class Codes: H01L 31/02363 of the semiconductor body itself, e.g. textured active layers
• CPC Class Codes: H01L 31/035236 Superlattices; Multiple quantum well structures
• CPC Class Codes: H01L 31/035281 Shape of the body
• CPC Class Codes: H01L 31/03529 Shape of the potential jump barrier or surface barrier
• CPC Class Codes: H01L 31/184 the active layers comprising only AIIIBV compounds, e.g. GaAs, InP
• CPC Class Codes: H01L 31/1852 comprising a growth substrate not being an AIIIBV compound
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/24 of the light emitting region, e.g. non-planar junction
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: Y02E 10/544 Solar cells from Group III-V materials

Abstract

A semiconductor sensor, solar cell or emitter, or a precursor therefor, has a substrate and one or more textured semiconductor layers deposited onto the substrate. The textured layers enhance light extraction or absorption. Texturing in the region of multiple quantum wells greatly enhances internal quantum efficiency if the semiconductor is polar and the quantum wells are grown along the polar direction. Electroluminescence of LEDs of the invention is dichromatic, and results in variable color LEDs, including white LEDs, without the use of phosphor.

Claims

1. A semiconductor device for use as an emitter, the device comprising:

a substrate comprising a material selected from the group consisting of sapphire, silicon carbide, zinc oxide, silicon, gallium arsenide, gallium nitride, aluminum nitride and aluminum gallium nitride;

a first layer on said substrate comprising a III-nitride semiconductor, wherein a surface of the first layer has a randomly textured topology, the first layer is n-type doped, and the first layer is electrically connected to a first contact;

one or more quantum well layers alternating with barrier layers and textured by the surface of the first layer, the barrier layers comprising a III-nitride semiconductor and the quantum well layers comprising a III-nitride semiconductor; and

an upper layer comprising a III-nitride semiconductor, wherein the upper layer is textured by the surface of the adjacent quantum well layer, the upper layer is p-type doped, and the upper layer is electrically connected to a second contact;

wherein the electroluminescence spectrum of the device is controlled by passing a current through the device between said first and second contacts.

2. The semiconductor device of claim 1, wherein said substrate is randomly surface textured and said first and subsequent layers replicate substrate texturing.

3. The semiconductor device of claim 1, wherein the substrate comprises a material selected from the group consisting of (0001) sapphire, (19-12) sapphire, (19-10) sapphire, (11-20) sapphire, (0001) silicon carbide, (0001) zinc oxide, (111) silicon, (111) gallium arsenide, (0001) gallium nitride and (0001) aluminum nitride and (0001) AlGaN.

4. The semiconductor device of claim 1, wherein the substrate comprises a textured surface on a side facing said first layer.

5. The semiconductor device of claim 1, wherein the substrate comprises a textured surface on a side away from said first layer.

6. The semiconductor device of claim 1, wherein the substrate comprises a polished surface on a side facing said first layer.

7. The semiconductor device of claim 1, wherein the surface of the substrate is textured by lithography or etching.

8. The semiconductor device of claim 1, wherein the first layer is a deposition on the substrate resulting from one of hydride vapor phase epitaxy, metal-organic chemical vapor deposition, molecular beam epitaxy, liquid phase epitaxy, laser ablation or a combination of such methods.

9. The semiconductor device of claim 8, wherein the first layer is a result of hydride vapor phase epitaxy of the III-nitride semiconductor material thereon in the presence of excess HCl.

10. The semiconductor device of claim 9, wherein the molar ratio of NH₃ to HCl in the hydride vapor phase epitaxy process is from 5:

1 to 10;

1.

11. The semiconductor device of claim 9, wherein the quantum well layers and barrier layers are the result of molecular beam epitaxy.

12. The semiconductor device of claim 8, wherein the first layer is a result of molecular beam epitaxy in the presence of a molar excess of N over Ga.

13. The semiconductor device of claim 1, wherein one or more quantum well layers are grown by one of hydride vapor phase epitaxy, metal-organic chemical vapor deposition, molecular beam epitaxy, liquid phase epitaxy, laser ablation or a combination of these methods.

14. The semiconductor device of claim 1, wherein the electroluminescence spectrum of the device comprises two or more peaks.

15. The semiconductor device of claim 14, wherein the multiple quantum wells comprise interspersed regions having quantum well layers of different thickness.

16. The semiconductor device of claim 15, wherein the quantum well layers in flat regions of the multiple quantum wells are thicker than the quantum well layers in inclined regions of the multiple quantum wells.

17. The semiconductor device of claim 14, wherein one of said peaks is in the range of 390-450 nm and the other peak is in the range of 500-600 nm.

18. The semiconductor device of claim 14, wherein increasing the current through the device between said first and second contacts increases the electroluminescence at one of said peaks relative to the other.

19. The semiconductor device of claim 18, wherein the peak that increases is in the range of 390-450 nm.

20. The semiconductor device of claim 18, wherein the color temperature of the electroluminescence is blue-shifted by increasing the current through the device between said first and second contacts.

21. The semiconductor device of claim 1 whose electroluminescence is white.

22. The semiconductor device of claim 1 whose electroluminescence is characterized by a color temperature in the range of 2500°

K-7500°

K.

23. The semiconductor device of claim 1 further comprising a phosphor.

24. The semiconductor device of claim 23, wherein the phosphor has an emission peak in the range of 500-700 nm.

29. A variable color indicator, comprising:

the semiconductor device of claim 1;

and

a controller for setting the current through the device between said first and second contacts in response to an input signal, wherein a change in the input signal results in a change in the color of light emitted by the device.

30. A variable color illumination device comprising:

one or more semiconductor devices of claim 1;

and

a controller for setting the current through each of the devices between said first and second contacts in response to one or more input signals, wherein a change in the input signals results in a change in the intensity and color of the light emitted by the semiconductor device.

31. The illumination device of claim 30, wherein a plurality of said semiconductor devices are arranged in an array.

32. The illumination device of claim 30 comprising a plurality of said semiconductor devices, wherein each semiconductor device is independently controlled.

33. The illumination device of claim 30 comprising a plurality of said semiconductor devices, wherein the semiconductor devices are controlled in unison.

34. A two-dimensional color display, comprising:

a two-dimensional array comprising a plurality of the semiconductor devices of claim 1;

and

a controller for setting the current through each semiconductor device between said first and second contacts in response to an input signal, wherein the input signal results in the formation of a color pattern of light emitted by the semiconductor devices.

35. The color display of claim 34, wherein the color pattern forms an image viewable by looking at the array.

36. The display of claim 35 which forms a still image.

37. The display of claim 35 which forms a moving image.

38. A projector, comprising:

a two-dimensional array comprising a plurality of the semiconductor devices of claim 1;

and

a controller for setting the current through each semiconductor device between said first and second contacts in response to an input signal, wherein the input signal results in the formation of a color pattern of light emitted by the semiconductor devices and projected onto a viewing screen.

39. The projector of claim 38, wherein the color pattern forms an image on the viewing screen.

40. The projector of claim 38 which is a still-image projector.

41. The projector of claim 38 which is a motion picture projector.

25. A method of controlling the emission spectrum of a light emitting diode, comprising the steps of:

providing a light emitting diode, comprising;

a substrate comprising a material selected from the group consisting of sapphire, silicon carbide, zinc oxide, silicon, gallium arsenide, gallium nitride, aluminum nitride and aluminum gallium nitride;

a first layer on said substrate comprising a III-nitride semiconductor, wherein a surface of the first layer has a randomly textured topology, the first layer is n-doped, and the first layer is electrically connected to a first contact;

one or more quantum well layers alternating with barrier layers and textured by the surface of the first layer, the barrier layers comprising a III-nitride semiconductor and the quantum well layers comprising a III-nitride semiconductor; and

an upper layer comprising a III-nitride semiconductor, wherein the upper layer is textured by the surface of the quantum well layer farthest from the first layer, the upper layer is p-type doped, and the upper layer is electrically connected to a second contact; and

passing a current through the device between said first and second contacts;

wherein the electroluminescence spectrum of the diode is controlled by said current.

26. The method of claim 25, wherein the electroluminescence spectrum of the diode comprises two or more peaks, and increasing the current through the device between said first and second contacts increases the electroluminescence at one of said peaks relative to the other.

27. The method of claim 26, wherein the electroluminescence at a peak in the range of 390-450 nm increases relative to one or more other peaks.

28. The method of claim 26, wherein the color temperature of the electroluminescence is blue-shifted by increasing the current through the device between said first and second contacts.