Emitting device with compositional and doping inhomogeneities in semiconductor layers
A device including one or more layers with lateral regions configured to facilitate the transmission of radiation through the layer and lateral regions configured to facilitate current flow through the layer is provided. The layer can comprise a short period superlattice, which includes barriers alternating with wells. In this case, the barriers can include both transparent regions, which are configured to reduce an amount of radiation that is absorbed in the layer, and higher conductive regions, which are configured to keep the voltage drop across the layer within a desired range.
1. A device comprising:
a short period superlattice (SPSL) semiconductor layer comprising a plurality of barriers, wherein a composition of at least one barrier varies along lateral dimensions of the at least one barrier such that a lateral cross section of the at least one barrier includes:
a set of transparent regions having a first characteristic band gap, wherein the set of transparent regions are at least ten percent of an area of the lateral cross section of the at least one barrier; and
a set of higher conductive regions having a second characteristic band gap at least five percent smaller than the first characteristic band gap, wherein the set of higher conductive regions occupies a sufficient area of the area of the lateral cross section of the at least one barrier to keep a voltage drop across the SPSL within a target range, and wherein lateral inhomogeneities in at least one of: the composition or a doping of the at least one barrier forms the set of transparent regions and the set of higher conductive regions.
2. The device of claim 1 , wherein each transparent region has a transmission coefficient for a target radiation wavelength, l, greater than or equal to approximately fifty percent.
3. The device of claim 1 , wherein the set of higher conductive regions has an average resistance per unit area to a vertical current flow resulting in a total voltage drop across the SPSL of less than approximately ten percent of the total voltage drop across the device.
4. The device of claim 1 , wherein a characteristic distance between two higher conductive regions in the set of higher conductive regions is less than a lateral current spreading length.
5. The device of claim 1 , wherein the set of transparent regions and the set of higher conductive regions are formed using nano-scale inhomogeneities.
6. The device of claim 1 , wherein the set of transparent regions forms a photonic crystal.
7. The device of claim 1 , wherein the set of higher conductive regions form an interconnected network of conductive paths.
8. A device comprising:
a short period superlattice (SPSL) semiconductor layer comprising a plurality of barriers, wherein a lateral cross section of each barrier includes:
a set of transparent regions, wherein the set of transparent regions are at least ten percent of an area of the lateral cross section of the at least one barrier; and
a set of higher conductive regions occupying a sufficient area of the area of the lateral cross section of the at least one barrier to keep a voltage drop across the SPSL within a target range, wherein a characteristic distance between two higher conductive regions in the set of higher conductive regions is less than a lateral current spreading length.
9. The device of claim 8 , wherein each transparent region has a transmission coefficient for a target radiation wavelength, l, greater than or equal to approximately fifty percent.
10. The device of claim 8 , wherein the set of higher conductive regions has an average resistance per unit area to a vertical current flow resulting in a total voltage drop across the SPSL of less than approximately ten percent of the total voltage drop across the device.
11. The device of claim 8 , wherein lateral inhomogeneities in at least one of: a composition of a barrier or a doping of each barrier forms the set of transparent regions and the set of higher conductive regions.
12. The device of claim 8 , wherein the set of transparent regions and the set of higher conductive regions are formed using nano-scale inhomogeneities.
13. The device of claim 8 , wherein the set of transparent regions forms a photonic crystal.
14. The device of claim 8 , wherein the set of higher conductive regions is interspersed with the set of transparent regions to form an interconnected network of conductive paths.
15. A method of fabricating a device comprising:
forming a short period superlattice (SPSL) semiconductor layer comprising a plurality of barriers, wherein a lateral cross section of each barrier includes:
a set of transparent regions, wherein the set of transparent regions are at least ten percent of an area of the lateral cross section of the at least one barrier; and
a set of higher conductive regions occupying a sufficient area of the area of the lateral cross section of the at least one barrier to keep a voltage drop across the SPSL within a target range, wherein a characteristic distance between two higher conductive regions in the set of higher conductive regions is less than a lateral current spreading length.
16. The method of claim 15 , wherein the forming includes forming each transparent region to have a transmission coefficient for a target radiation wavelength, l, greater than or equal to approximately fifty percent.
17. The method of claim 15 , wherein the forming includes forming the set of higher conductive regions to have an average resistance per unit area to a vertical current flow resulting in a total voltage drop across the SPSL of less than approximately ten percent of the total voltage drop across the device.
18. The method of claim 15 , wherein the forming includes forming the set of transparent regions to form a photonic crystal.
19. The method of claim 15 , wherein forming includes interspersing the set of higher conductive regions with the set of transparent regions such that the set of higher conductive regions forms an interconnected network of conductive paths.
20. The method of claim 15 , wherein the forming includes forming the set of transparent regions and the set of higher conductive regions using a non-uniform barrier thickness of each barrier.
21. The method of claim 15 , wherein the forming includes forming the set of transparent regions and the set of higher conductive regions using a non-uniform compositional distribution or a non-uniform doping distribution along the barrier thickness of each barrier.
22. The method of claim 15 , wherein the forming includes forming the set of transparent regions and the set of higher conductive regions using a non-uniform doping distribution along the barrier thickness of each barrier.
23. The method of claim 15 , further comprising forming an inhomogeneous layer, wherein the SPSL semiconductor layer is formed directly on the inhomogeneous layer, and wherein at least a portion of the forming the inhomogeneous layer is performed at an inhomogeneous growth temperature at least approximately two hundred degrees Celsius lower than a temperature for forming the SPSL semiconductor layer.
24. The method of claim 15 , wherein forming the inhomogeneous layer includes:
enabling three-dimensional islands to coalesce at the inhomogeneous growth temperature; and
enabling two-dimensional growth around the islands at a growth temperature comparable to the temperature for forming the SPSL semiconductor layer.