Laterally contacted blue LED with superlattice current spreading layer
View Patent ↗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.
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.