III-P LIGHT EMITTING DEVICE WITH A SUPERLATTICE

1 . A device comprising:

a semiconductor structure comprising a III-P light emitting layer disposed between an n-type region and a p-type region, the n-type region comprising a superlattice; and

an n-contact metal on and in contact with a surface of the superlattice opposite the III-P light emitting layer,

the superlattice comprising a plurality of stacked layer pairs, each layer pair comprising a first layer of Al x Ga 1−x InP where 0<x<1 and a second layer of Al y Ga 1−y InP where 0<y<1, the first layer having a smaller aluminum composition than the second layer.

2 . The device of claim 1 further comprising:

a bottom contact disposed on the p-type region.

3 . The device of claim 1 wherein 0.3≦x≦0.4 and 0.4≦y≦0.5.

4 . The device of claim 1 wherein 0.2≦x≦0.5 and 0.3≦y≦0.65.

5 . The device of claim 1 wherein the first and second layers are doped with an n-type dopant.

6 . The device of claim 1 wherein at least one of the first and second layers is strained relative to a growth substrate on which the semiconductor structure is grown.

7 . The device of claim 1 wherein the superlattice is lattice matched to a growth substrate on which the semiconductor structure is grown.

8 . A method comprising:

growing an n-type superlattice on a growth substrate, the superlattice comprising a plurality of stacked layer pairs, each layer pair comprising a first layer of AlGaInP and a second layer of AlGaInP, the first layer having a smaller aluminum composition than the second layer;

forming a first metal contact on the p-type region;

growing a light emitting region directly on the n-type superlattice;

growing a p-type region on the light emitting region;

removing the growth substrate to expose a surface of the superlattice; and

forming a second metal contact directly on the exposed surface of the superlattice.

9 . The method of claim 8 wherein 0.2≦x≦0.5 and 0.3≦y≦0.65.

10 . The method of claim 8 further comprising lattice matching the superlattice to the growth substrate.

11 . The method of claim 8 further comprising growing at least one of the first and second layers strained relative to the growth substrate.

12 . The method of claim 8 further comprising roughening or patterning the exposed surface of the superlattice.

13 . The method of claim 8 wherein forming a second metal contact directly on the exposed surface of the superlattice comprises:

forming a metal layer directly on the surface of the superlattice; and

patterning the metal layer to form a shaped second metal contact, the shape having a width no less than 1 micron and no greater 30 microns in a plan view.

14 . The device of claim 1 wherein the superlattice layers are doped with a doping profile changing across the superlattice.

15 . The device of claim 1 wherein the first layers are more highly doped than the second layers.

16 . The device of claim 1 , wherein the second layers are more highly doped than the first layers.

17 . The device of claim 1 , wherein the n-contact layer is patterned to have a shape, the shape having a width no less than 1 micron and no greater 30 microns in a plan view.

18 . The device of claim 17 , wherein the shape has a width no less than 1 micron and no greater than 20 microns.

19 . A device comprising:

a semiconductor structure comprising a III-P light emitting layer disposed between an n-type region and a p-type region, the n-type region comprising a superlattice;

a current spreading layer on and in contact with a surface of the superlattice opposite the III-P light emitting layer; and

an n-contact on and in contact with the current spreading layer,

the superlattice comprising a plurality of stacked layer pairs, each layer pair comprising a first layer of Al x Ga 1−x InP where 0<x<1 and a second layer of Al y Ga 1−y InP where 0<y<1, the first layer having a smaller aluminum composition than the second layer.

20 . The device of claim 19 , wherein the current spreading layer comprises indium tin oxide or zinc oxide.