High efficency LED structure

• US 5,614,734 A
• Filed: 03/15/1995
• Issued: 03/25/1997
• Est. Priority Date: 03/15/1995
• Status: Expired due to Term

• Current Assignee: Yale University
• Original Assignee: Yale University
• Inventors: Guido, Louis J.
• Primary Examiner(s): MEIER, STEPHEN D
• Application Number:
  US08/404,592
• Time in Patent Office: 741 Days
• Field of Search: 257/94, 257/95
• US Class Current: 257/94
• CPC Class Codes: H01L 2224/04042 Bonding areas specifically adapted for wire connectors, e.g. wirebond pads
• CPC Class Codes: H01L 2224/48463 the connecting portion on the bonding area of the semiconductor or solid-state body being a ball bond
• CPC Class Codes: H01L 24/05 of an individual bonding area
• CPC Class Codes: H01L 27/153 in a repetitive configuration, e.g. LED bars
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/12041 LED
• CPC Class Codes: H01L 2924/12042 LASER
• CPC Class Codes: H01L 33/105 with a resonant cavity structure
• CPC Class Codes: H01L 33/14 with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure
• CPC Class Codes: H01L 33/30 containing only elements of Group III and Group V of the Periodic Table
• CPC Class Codes: H01L 33/42 Transparent materials

Abstract

An LED structure including a distributed Bragg reflector having multiple periods, each period including at least a first layer made of a first indirect band gap material and a second layer made of a second indirect band gap material, the first band gap material having a higher index of refraction than the second indirect band gap material; and a light emitting diode formed on top of the distributed Bragg reflector, the light emitting diode having a top layer and a bottom layer, the bottom layer being proximate to the distributed Bragg reflector.

Claims

1. An LED structure comprising:

a distributed Bragg reflector including multiple periods, each period comprising at least a first layer made of a first indirect band gap material and a second layer made of a second indirect band gap material, said first band gap material having a higher index of refraction than said second indirect band gap material;

a semiconductor light emitting diode formed on top of the distributed Bragg reflector, said light emitting diode having a top layer and a bottom layer, said bottom layer being proximate to said distributed Bragg reflector; and

an isolation region extending from the top layer of light emitting diode down through the distributed Bragg reflector, said isolation region having an interior defining a light emitting pixel element, said isolation region formed by an impurity-induced layer disordering technique.

2. The LED structure of claim 1 wherein said second layer is made of Al_x Ga.sub.(1-x) As, where x is at least as great as 0.4.

3. The LED structure of claim 2 wherein x is at least as great as 0.6.

4. The LED structure of claim 3 wherein x is at least as great as 0.8.

5. The LED structure of claim 2 wherein said first layer is made of AlAs.

6. The LED structure of claim 1 wherein said second layer is made of (Al_x Ga_1-x)₀.5 In₀.5 P., where x is at least as great as 0.7.

7. The LED structure of claim 6 wherein said first layer is made of Al₀.5 In₀.5 P.

8. The LED structure of claim 1 wherein the light emitting diode is a double heterostructure light emitting device comprising a first confining layer, a second confining layer and an active region sandwiched between said first and second confining layers, wherein said top and bottom layers are said first and second confining layers, respectively.

9. The LED structure of claim 1 further comprising an In₂ O₃ current spreading layer.

10. The LED structure of claim 9 further comprising a cap layer between the current spreading layer and the rest of said LED structure, said cap layer comprising a doped semiconductor material that functions to reduce electrical resistance between the current spreading layer and the rest of the LED structure.

11. The LED structure of claim 10 wherein the cap layer comprises p⁺ -type GaAs.

12. The LED structure of claim 11 wherein said cap layer has a p-type doping level that is greater than about 8×

10¹⁸ cm^-3.

13. An LED structure comprising:

a semiconductor light emitting diode having a top layer and a bottom layer and a light emitting region;

a cap layer above the light emitting diode, said cad layer being a p-type semiconductor material;

an In₂ O₃ current spreading layer formed on top of the cap layer; and

a metal contact pad formed on top of a portion of the In₂ O₃ current spreading layer above the active region leaving an unobstructed portion of the In₂ O₃ current spreading layer through which light generated in the light emitting active region passes out of the LED structure.

14. The LED structure of claim 13 wherein the light emitting diode is a double heterostructure light emitting device comprising a first confining layer, a second confining layer and an active region sandwiched between said first and second confining layers, wherein said top and bottom layers are said first and second confining layers, respectively.

15. The LED structure of claim 13 further comprising a distributed Bragg reflector formed below the bottom layer of said light emitting diode.

16. The LED structure of claim 15 wherein said distributed Bragg reflector includes multiple periods, each period comprising at least a first layer made of a first indirect band gap material and a second layer made of a second indirect band gap material, said first indirect band gap material having a higher index of refraction than said second indirect band gap material.

17. The LED structure of claim 16 wherein said second layer is made of Al_x Ga.sub.(1-x) As, where x is at least as great as 0.4.

18. The LED structure of claim 17 wherein x is at least as great as 0.6.

19. The LED structure of claim 18 wherein x is at least as great as 0.8.

20. The LED structure of claim 18 wherein said first layer is made of AlAs.

21. The LED structure of claim 16 wherein said second layer is made of (Al_x Ga_1-x)₀.5 In₀.5 P., where x is at least as great as 0.7.

22. The LED structure of claim 13 wherein said unobstructed portion has an area that is at least as large as 50% of the area of the light emitting region.

23. The LED structure of claim 13 wherein the cap layer comprises p⁺ -type GaAs.

24. The LED structure of claim 23 wherein said cap layer has a p-type doping level that is greater than about 8×

10¹⁸ cm^-3.