High brightness LED utilizing a roughened active layer and conformal cladding
View Patent ↗A light emitting device and method for making the same are disclosed. The device includes an active layer disposed between first and second layers. The first layer has top and bottom surfaces. The top surface includes a first material of a first conductivity type, including a plurality of pits in the substantially planar surface. The active layer overlies the top surface of the first layer and conforms to the top surface, the active layer generating light characterized by a wavelength when holes and electrons recombine therein. The second layer includes a second material of a second conductivity type, the second layer overlying the active layer and conforming to the active layer. The device can be constructed on a substrate having a lattice constant sufficiently different from that of the first material to give rise to dislocations in the first layer that are used to form the pits.
1. A device comprising:
a first layer having top and bottom surfaces, said top surface comprising a first material of a first conductivity type and including a plurality of pits in a substantially planar surface, said top and bottom surfaces being characterized by a distance between said top and bottom surfaces, said distance being less in said pits than in said areas outside said pits;
an active layer overlying said top surface of said first layer, said active layer generating light characterized by a wavelength when holes and electrons recombine therein;
a second layer comprising a second material of a second conductivity type, said second layer comprising a cladding layer having a top surface and a bottom surface, said bottom surface overlying said active layer and conforming to said active layer, said top surface having depressions therein that extend into said pits; and
a substrate on which said first layer is constructed, said substrate having a lattice constant sufficiently different from that of said first material to give rise to dislocations in said first layer, said pits being characterized by a bottom point that is closest to said substrate, said pits being located such that said bottom point of each of said pits lies on a different one of said dislocations.
2. The device of claim 1 wherein said pits have a dimension that is greater than said wavelength of light generated by said active layer.
3. The device of claim 1 further comprising a layer of electrically conducting material having a top surface and a bottom surface, said top surface of said layer of electrically conducting material overlying said top surface of said second layer and conforming to said top surface of said second layer.
4. The device of claim 3 wherein said layer of electrically conducting material is transparent to said light generated in said active layer.
5. The device of claim 4 wherein said top surface of said layer of electrically conducting material extends into said pits.
6. The device of claim 1 wherein said substrate is chosen from the group consisting of sapphire, SiC, silicon, AlN, and said first material comprises a material from the GaN family of materials.
7. The device of claim 1 wherein said dislocations are present at a density greater than 10 7 dislocations per cm 2 .
8. The device of claim 3 wherein said top surface of said electrically conducting material is substantially planar between said pits.