Anisotropic strain control in semipolar nitride quantum wells by partially or fully relaxed aluminum indium gallium nitride layers with misfit dislocations

Abstract

An epitaxial structure for a III-Nitride based optical device, comprising an active layer with anisotropic strain on an underlying layer, where a lattice constant and strain in the underlying layer are partially or fully relaxed in at least one direction due to a presence of misfit dislocations, so that the anisotropic strain in the active layer is modulated by the underlying layer.

What is claimed is: 
     
         1 . A device structure, comprising:
 a semipolar or nonpolar III-Nitride active layer formed on or above an at least partially relaxed III-nitride layer, wherein the semipolar or nonpolar III-Nitride active layer is strained with respect to the at least partially relaxed III-nitride layer.   
     
     
         2 . The device of  claim 1 , further comprising:
 a non-polar or semi-polar surface of a III-nitride substrate; and   the at least partially relaxed III-nitride layer on or above the non-polar or semi-polar surface of the substrate.   
     
     
         3 . The device of  claim 2 , wherein the substrate is a GaN substrate. 
     
     
         4 . The device of  claim 2 , wherein the semipolar or nonpolar III-Nitride active layer is formed with anisotropic strain on or above the at least partially relaxed III-nitride layer. 
     
     
         5 . The device of  claim 4 , wherein the anisotropic strain comprises a different strain in different directions of the III-nitride active layer, the different directions including:
 a first direction that is parallel to an in-plane c-projection and a second direction perpendicular to the first direction.   
     
     
         6 . The device of  claim 5 , wherein the at least partially relaxed III-nitride layer is relaxed along the first direction and is not relaxed along the second direction, and the surface of the substrate is a semipolar plane. 
     
     
         7 . The device of  claim 1 , further comprising:
 the active layer comprising one or more quantum wells having a thickness greater than 3 nanometers and with an Indium composition and strain such that the active layer emits light with a peak wavelength corresponding to green light.   
     
     
         8 . The device of  claim 1 , further comprising:
 the active layer comprising one or more quantum wells having a thickness greater than 3 nanometers and with an Indium composition and strain such that the active layer emits light with an X2 polarization.   
     
     
         9 . The device of  claim 8 , wherein the device is a laser diode with a cavity bounded by cleaved m-plane facets. 
     
     
         10 . The device of  claim 1 , wherein up to 50% of strain in the active layer is relaxed. 
     
     
         11 . The device of  claim 1 , wherein the at least partially relaxed III-nitride layer is InGaN. 
     
     
         12 . The device of  claim 1 , wherein the at least partially relaxed III-nitride layer has between 10% and 30% Indium composition and the active layer comprises one or more InGaN quantum wells with between 10% and 30% Indium composition. 
     
     
         13 . The device of  claim 1 , wherein the at least partially relaxed III-nitride layer is AlGaN. 
     
     
         14 . The device of  claim 13 , wherein the device emits light having a peak wavelength corresponding to ultraviolet light. 
     
     
         15 . The device of  claim 1 , wherein the at least partially relaxed III-nitride layer is a superlattice. 
     
     
         16 . The device of  claim 1 , wherein the active layer is free of dislocations. 
     
     
         17 . The device of  claim 1 , wherein the at least partially relaxed III-nitride layer, the non-polar or semi-polar III-nitride active layer, and anisotropic strain in the non-polar or semi-polar III-nitride active layer, are selected to obtain a desired operation wavelength for the optical device. 
     
     
         18 . The device of  claim 1 , wherein the at least partially relaxed III-nitride layer and the non-polar or semi-polar III-nitride active layer are semipolar layers. 
     
     
         19 . A method of fabricating a device, comprising:
 growing a semipolar or nonpolar III-Nitride active layer on or above an at least partially relaxed III-nitride layer, wherein the semipolar or nonpolar III-Nitride active layer is strained with respect to the at least partially relaxed III-nitride layer.   
     
     
         20 . The method of  claim 19 , further comprising:
 growing the at least partially relaxed III-nitride layer on or above a non-polar or semi-polar surface of a III-nitride substrate.   
     
     
         21 . The method of  claim 20 , wherein the substrate is a GaN substrate. 
     
     
         22 . The method of  claim 20 , further comprising:
 controlling a lattice mismatch between the active layer and the at least partially relaxed III-nitride layer to control a strain in a first direction of the active layer; and   controlling a lattice mismatch between the active layer and the III-nitride substrate to control the strain in a second direction of the active layer perpendicular to the first direction.   
     
     
         23 . The method of  claim 19 , further comprising controlling strain anisotropy in the semipolar or nonpolar III-Nitride active layer order to control at least one property selected from optical gain, bandstructure, luminescence polarization, and optical matrix elements. 
     
     
         24 . The method of  claim 19 , wherein the at least partially relaxed III-nitride layer is grown non-coherently on a substrate and the semipolar or nonpolar III-Nitride active layer is grown coherently on the at least partially relaxed III-nitride layer. 
     
     
         25 . The method of  claim 24 , wherein the at least partially relaxed III-nitride layer is relaxed in one direction that depends on one or more of a semipolar orientation and alloy composition of the substrate and the at least partially relaxed III-nitride layer. 
     
     
         26 . The method of  claim 19 , wherein the at least partially relaxed III-nitride layer and the non-polar or semi-polar III-nitride active layer are semipolar layers.