Semiconductor Heterostructure with P-type Superlattice

Abstract

A heterostructure for an optoelectronic device is disclosed. The heterostructure includes an active region including at least one quantum well and at least one barrier and an electron blocking layer located adjacent to the active region, wherein the electron blocking layer includes a region of graded composition. An asymmetric p-type superlattice layer is located adjacent to the electron blocking layer, wherein the p-type superlattice includes at least one superlattice period comprising a set of wells and a set of barriers. A thickness of at least one of: each well in the set of wells or each barrier in the set of barriers varies along a length of the p-type superlattice.

What is claimed is: 
     
         1 . A heterostructure comprising:
 an active region including at least one quantum well and at least one barrier;   an electron blocking layer located adjacent to the active region, wherein the electron blocking layer includes a region of graded composition; and   an asymmetric p-type superlattice layer located adjacent to the electron blocking layer, wherein the p-type superlattice layer includes at least one superlattice period comprising a plurality of wells and a plurality of barriers, and wherein a thickness of at least one of: each well in the plurality of wells or each barrier in the plurality of barriers varies along a length of the p-type superlattice layer.   
     
     
         2 . The heterostructure of  claim 1 , wherein the electron blocking layer includes a region of constant composition adjacent to the region of graded composition. 
     
     
         3 . The heterostructure of  claim 1 , wherein the electron blocking layer includes a second region of graded composition. 
     
     
         4 . The heterostructure of  claim 1 , wherein an interface between the active region and the electron blocking layer includes a graded region that increases from a composition of the at least one barrier of the active region to a maximum composition of the electron blocking layer. 
     
     
         5 . The heterostructure of  claim 1 , wherein the thickness of each well in the plurality of wells increases along the length of the p-type superlattice layer and away from the electron blocking layer. 
     
     
         6 . The heterostructure of  claim 1 , wherein the thickness of each barrier in the plurality of barriers decreases along the length of the p-type superlattice layer and away from the electron blocking layer. 
     
     
         7 . The heterostructure of  claim 1 , further comprising a p-type contact layer located adjacent to the p-type superlattice layer. 
     
     
         8 . The heterostructure of  claim 7 , wherein the p-type contact layer includes a p-type dopant concentration of at least 10 18  dopants/cm 2 . 
     
     
         9 . The heterostructure of  claim 1 , wherein a composition of a well in the plurality of wells in the p-type superlattice layer is higher than a composition of the at least one quantum well in the active region. 
     
     
         10 . The heterostructure of  claim 1 , wherein an average bandgap of each barrier and well pair of the p-type superlattice layer is larger than an average bandgap of the active region. 
     
     
         11 . An optoelectronic device comprising:
 an n-type contact layer;   an active region including at least one quantum well and at least one barrier located adjacent to the n-type contact layer;   an electron blocking layer located adjacent to the active region, wherein the electron blocking layer includes a region of graded composition;   a p-type superlattice layer located adjacent to the electron blocking layer, wherein the p-type superlattice layer includes at least one superlattice period comprising a plurality of wells and a plurality of barriers, and wherein a thickness of at least one of: each well in the plurality of wells or each barrier in the plurality of barriers varies along a length of the p-type superlattice layer; and   a p-type contact layer located adjacent to the p-type superlattice layer, wherein the p-type contact layer has a thickness less than 15 nanometers.   
     
     
         12 . The device of  claim 11 , wherein the electron blocking layer includes a region of constant composition adjacent to the region of graded composition. 
     
     
         13 . The device of  claim 11 , wherein the electron blocking layer includes a second region of graded composition. 
     
     
         14 . The device of  claim 11 , wherein an interface between the active region and the electron blocking layer includes a graded region that increases from a composition of the at least one barrier of the active region to a maximum composition of the electron blocking layer. 
     
     
         15 . The device of  claim 11 , wherein the thickness of each well in the plurality of wells increases along the length of the p-type superlattice and away from the electron blocking layer. 
     
     
         16 . The device of  claim 11 , wherein the thickness of each barrier in the plurality of barriers decreases along the length of the p-type superlattice and away from the electron blocking layer. 
     
     
         17 . The device of  claim 11 , wherein the p-type contact layer includes a p-type dopant concentration of at least 10 18  dopants/cm 2 . 
     
     
         18 . The device of  claim 11 , wherein a composition of a well in the set of wells in the p-type superlattice is higher than a composition of the at least one quantum well in the active region. 
     
     
         19 . The device of  claim 11 , wherein an average bandgap of each barrier and well pair of the p-type superlattice layer is larger than an average bandgap of the active region. 
     
     
         20 . An optoelectronic device comprising:
 a group III nitride n-type contact layer;   a group III nitride active region including at least one quantum well and at least one barrier, wherein the active region is located adjacent to the n-type contact layer;   a group III nitride electron blocking layer located adjacent to the active region, wherein the electron blocking layer includes a region of graded composition;   a group III nitride p-type superlattice layer located adjacent to the electron blocking layer, wherein the p-type superlattice layer includes at least one superlattice period comprising a plurality of wells and a plurality of barriers, and wherein a thickness of at least one of: each well in the plurality of wells or each barrier in the plurality of barriers varies along a length of the p-type superlattice layer; and   a group III nitride p-type contact located adjacent to the p-type superlattice layer.