Laterally contacted blue LED with superlattice current spreading layer

• US 8,395,165 B2
• Filed: 07/08/2011
• Issued: 03/12/2013
• Est. Priority Date: 07/08/2011
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Bridelux Incorporated
• Inventors: Chen, Zhen, Fenwick, William, Lester, Steve
• Primary Examiner(s): Vu, David
• Application Number:
  US13/178,497
• Publication Number:
  US 20130009130A1
• Time in Patent Office: 613 Days
• Field of Search: 257/78, 257/79, 257/E33.049, 257/E33.034, 257/E33.008, 438/22, 438/28, 438/29
• US Class Current: 257/79
• CPC Class Codes: H01L 33/04 with a quantum effect structure or superlattice, e.g. tunnel junction
• 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 33/32 containing nitrogen

Abstract

A laterally contacted blue LED device involves a PAN structure disposed over an insulating substrate. The substrate may be a sapphire substrate that has a template layer of GaN grown on it. The PAN structure includes an n-type GaN layer, a light-emitting active layer involving indium, and a p-type GaN layer. The n-type GaN layer has a thickness of at least 500 nm. A Low Resistance Layer (LRL) is disposed between the substrate and the PAN structure such that the LRL is in contact with the bottom of the n-layer. In one example, the LRL is an AlGaN/GaN superlattice structure whose sheet resistance is lower than the sheet resistance of the n-type GnA layer. The LRL reduces current crowding by conducting current laterally under the n-type GaN layer. The LRL reduces defect density by preventing dislocation threads in the underlying GaN template from extending up into the PAN structure.

Claims

1. A Light Emitting Diode (LED) device for emitting non-monochromatic light, the LED device comprising:

a substrate layer;

a low resistance layer disposed over the substrate layer, wherein the low resistance layer includes a plurality of periods, and wherein at least one of the periods of the low resistance layer includes an aluminum-gallium-nitride sublayer and a gallium-nitride sublayer;

an n-type layer disposed over and in contact with the low resistance layer, and wherein the n-type layer has a thickness of more than at least five hundred nanometers;

an active layer disposed over the n-type layer, wherein the active layer includes a plurality of periods, and wherein at least one of the periods of the active layer includes an indium-gallium-nitride sublayer and a gallium-nitride sublayer;

a p-type layer disposed over the active layer;

a first electrode disposed on and in electrical contact with at least a portion of the n-type layer; and

a second electrode disposed on and in electrical contact with at least a portion of the p-type layer, and wherein current flow between the first and second electrodes causes the non-monochromatic light to be emitted and to pass through the p-layer.

2. The LED device of claim 1, wherein the low resistance layer has a sheet resistance, wherein the n-type layer has a sheet resistance, and wherein the sheet resistance of the low resistance layer is smaller than the sheet resistance of the n-type layer.

3. The LED device of claim 1, wherein said aluminum-gallium-nitride sublayer of said at least one period of the low resistance layer is strained to a gallium-nitride sublayer of the low resistance layer.

4. The LED device of claim 3, wherein said aluminum-gallium-nitride sublayer of said at least one period of the low resistance layer is less than half as thick as said gallium-nitride sublayer of said at least one period of the low resistance layer.

5. The LED device of claim 3, wherein the aluminum-gallium-nitride sublayer of said at least one period has a thickness, wherein the gallium-nitride sublayer of said least one period of the low resistance layer has a thickness, and wherein the thickness of the gallium-nitride sublayer of said at least one period is substantially the same as the thickness of the gallium-nitride sublayer of said least at least one period.

6. The LED device of claim 1, further comprising:

a superlattice layer disposed between the n-type layer and the active layer, wherein the superlattice layer includes a plurality of periods, wherein at least one of the periods of the superlattice layer includes a first indium-gallium-nitride sublayer having a first indium concentration and includes a second indium-gallium-nitride sublayer having a second indium concentration, and wherein the first indium concentration is different from the second indium concentration.

7. The LED device of claim 1, further comprising:

a superlattice layer disposed between the n-type layer and the active layer, wherein the superlattice layer includes a plurality of periods, wherein at least one of the periods of the superlattice layer includes an indium-gallium-nitride sublayer and a gallium-nitride sublayer.

8. The LED device of claim 1, wherein the substrate layer is an insulative substrate layer that is substantially transparent to blue light.

9. The LED device of claim 1, wherein the substrate layer is a sapphire layer, and wherein the LED device further comprises:

a template layer disposed between the substrate layer and the low resistance layer, wherein the template layer is a layer of a material taken from the group consisting of;

undoped gallium-nitride and n-type gallium-nitride.

10. The LED device of claim 1, wherein the second electrode includes a transparent conductive layer and a bonding pad of metal.

11. A Light Emitting Diode (LED) device for emitting non-monochromatic light, the LED device comprising:

a sapphire substrate layer;

a low resistance layer disposed over the substrate layer, wherein the low resistance layer has a sheet resistance, wherein the low resistance layer includes a plurality of periods, and wherein at least one of the periods includes a gallium-nitride sublayer;

an n-type layer disposed over and in contact with the low resistance layer, wherein the n-type layer has a thickness of at least five hundred nanometers, wherein the n-type layer has a sheet resistance that is higher than the sheet resistance of the low resistance layer;

an active layer disposed over the n-type layer, wherein the active layer includes a plurality of periods, and wherein at least one of the periods of the active layer includes an indium-gallium-nitride sublayer and a gallium-nitride sublayer;

a p-type layer disposed over the active layer;

a first electrode disposed on and in electrical contact with at least a portion of the n-type layer; and

a second electrode in electrical disposed on and in electrical contact with at least a portion of the p-type layer, and wherein current flow between the first and second electrodes causes the non-monochromatic light to be emitted such that at least some of the light passes through the p-layer.

12. The LED device of claim 11, further comprising:

a strain release layer disposed between the n-type layer and the active layer.

13. A method comprising:

providing a low resistance layer over a sapphire substrate layer, wherein the low resistance layer comprises a plurality of periods, wherein at least one of the periods includes a gallium-nitride sublayer and an aluminum-gallium-nitride sublayer;

providing an n-type gallium-nitride layer on and in contact with the low resistance layer, wherein the n-type gallium-nitride layer has a thickness of at least five hundred nanometers, and wherein the n-type gallium-nitride layer has a sheet resistance that is larger than a sheet resistance of the low resistance layer;

providing an active layer comprising indium over the n-type gallium-nitride layer;

providing a p-type gallium-nitride layer over the active layer;

providing a first electrode that is disposed on and in electrical contact with at least a portion of the n-type gallium-nitride layer; and

providing a second electrode that is disposed on and in electrical contact with at least a portion of the p-type gallium-nitride layer such that conducting a current between the first and second electrodes will cause non-monochromatic light to be emitted from the active layer such that at least some of the light will pass through the p-type gallium-nitride layer.

14. The method of claim 13, wherein the sheet resistance of the low resistance layer is less than fifteen ohms per square at room temperature, and wherein the sheet resistance of the n-type gallium-nitride layer is more than fifteen ohms per square at room temperature.

15. A Light Emitting Diode (LED) device for emitting non-monochromatic light, the LED device comprising:

a substrate layer;

an n-type gallium-nitride layer having a thickness of at least five hundred nanometers;

an active layer disposed over the n-type gallium-nitride layer, wherein the active layer includes a plurality of periods, and wherein at least one of the periods of the active layer includes an amount of indium;

a p-type gallium-nitride layer disposed over the active layer;

a first electrode disposed on at least a portion of the n-type gallium-nitride layer;

a second electrode disposed on at least a portion of the p-type gallium-nitride layer such that a current flow between the first and second electrodes will cause the non-monochromatic light to be emitted and to pass through the p-type gallium-nitride layer; and

means for spreading current, wherein the means has a sheet resistance that is lower than a sheet resistance of the n-type gallium-nitride layer, and wherein the means is in contact with the n-type gallium-nitride layer and is disposed between the substrate layer and the n-type gallium-nitride layer.

16. The LED device of claim 15, wherein the substrate layer is a sapphire substrate layer, wherein the means for spreading current is disposed on and is in contact with a template layer of gallium-nitride, and wherein the template layer of gallium-nitride is disposed on and is in contact with the substrate layer.

17. The LED device of claim 16, wherein the means for spreading current comprises:

a sublayer of gallium-nitride; and

a sublayer of aluminum-gallium-nitride that is in contact with and is strained to the sublayer of gallium-nitride, wherein the sublayer of aluminum-gallium-nitride is less than half as thick as the sublayer of gallium-nitride.

18. A Light Emitting Diode (LED) device for emitting non-monochromatic light, the LED device comprising:

a sapphire substrate layer;

a superlattice layer disposed over the sapphire substrate layer, wherein the superlattice layer includes a plurality of periods, and wherein at least one of the periods of the low resistance layer includes an aluminum-gallium-nitride sublayer and a gallium-nitride sublayer;

an n-type gallium-nitride layer disposed over and in contact with the superlattice layer, and wherein the n-type gallium-nitride layer has a thickness of more than at least five hundred nanometers;

an active layer disposed over the n-type gallium-nitride layer, wherein the active layer includes a plurality of periods, and wherein at least one of the periods of the active layer includes an indium-gallium-nitride sublayer and a gallium-nitride sublayer;

a p-type gallium-nitride layer disposed over the active layer;

a first electrode disposed on and in electrical contact with at least a portion of the n-type gallium-nitride layer; and

a second electrode disposed on and in electrical contact with at least a portion of the p-type gallium-nitride layer, and wherein current flow between the first and second electrodes causes the non-monochromatic light to be emitted from the LED device.

19. The LED device of claim 18, wherein the superlattice layer is disposed on and is in contact with a template layer of gallium-nitride, and wherein the template layer of gallium-nitride is disposed on and is in contact with the sapphire substrate layer.