Low droop light emitting diode structure on gallium nitride semipolar substrates

Abstract

A light emitting diode structure of (Al,Ga,In)N thin films grown on a gallium nitride (GaN) semipolar substrate by metal organic chemical vapor deposition (MOCVD) that exhibits reduced droop. The device structure includes a quantum well (QW) active region of two or more periods, n-type superlattice layers (n-SLs) located below the QW active region, and p-type superlattice layers (p-SLs) above the QW active region. The present invention also encompasses a method of fabricating such a device.

What is claimed is: 
     
         1 . An opto-electronic device structure, comprising:
 a III-nitride light-emitting device structure, grown on or above a semipolar plane surface of a Group-III nitride substrate, wherein the light-emitting device structure has an External Quantum Efficiency (EQE) droop of 15% percent or less, as compared to a peak EQE, at a current density of 35 Amps per centimeter square (A/cm 2 ).   
     
     
         2 . The device structure of  claim 1 , wherein the device structure is a light emitting diode structure and the droop is in a range of 0.7%-15% at the current density in a range of 35 A/cm 2 -200 A/cm 2 . 
     
     
         3 . The device structure of  claim 2 , wherein the droop is in a range of 0.7%-10% for the current density in a range of 35 A/cm 2 -100 A/cm 2 . 
     
     
         4 . The device structure of  claim 2 , wherein the light emitting diode structure has an output power in a range of 50 milliwatts-266 milliwatts. 
     
     
         5 . The device structure of  claim 1 , wherein the droop is 15% or less at the current density at least 35 A/cm 2 . 
     
     
         6 . The device structure of  claim 1 , wherein the light-emitting device structure has a peak emission at a blue emission wavelength. 
     
     
         7 . The device structure of  claim 1 , wherein the Group-III nitride substrate is a Gallium Nitride (GaN) substrate. 
     
     
         8 . The device structure of  claim 7 , wherein the semi-polar plane surface is a semipolar (20-2-1) plane. 
     
     
         9 . The device structure of  claim 1 , further comprising an n-type superlattice comprising one or more indium (In) containing layers and gallium (Ga) containing layers. 
     
     
         10 . The device structure of  claim 1 , further comprising an n-type superlattice comprising layers having different III-nitride composition wherein each of the layers is doped with Silicon. 
     
     
         11 . The device structure of  claim 1 , further comprising an n-type superlattice (n-SL) located below an active region of the light-emitting device, wherein:
 the active region comprises one or more indium containing III-nitride quantum wells (QWs) with III-nitride barriers, the quantum wells having a QW number, a QW composition, and a QW thickness, the barriers having a barrier composition, barrier thickness, and barrier doping,   the n-SL comprises a number of periods, an SL doping, an SL composition, and layers each having a layer thickness, and   the QW number, the QW composition, the QW thickness, the barrier composition, the barrier thickness, the barrier doping, the number of periods, the SL doping, the SL composition, and the layer thickness are such that:   the LED has a peak emission at a blue emission wavelength or longer, and   the droop is 15% or less when the device is driven at a current density of 35 Amps per centimeter square (A/cm 2 ).   
     
     
         12 . The device structure of  claim 11 , further comprising a p-type III-nitride superlattice (p-SL) on or above the active region. 
     
     
         13 . The device structure of  claim 11 , wherein the active region emits light having a peak wavelength corresponding to light having a green wavelength or longer. 
     
     
         14 . The device structure of  claim 1 , further comprising:
 an n-type GaN layer on or above the semi-polar plane of the substrate, wherein the substrate is a GaN substrate having a roughened backside and the roughened backside extracts light from the light emitting device;   an n-type superlattice comprising alternating InGaN and GaN layers on or above the n-type GaN layer;   an active region, comprising InGaN multi quantum wells (MQWs) with GaN barriers, on or above the n-SL;   a p-type superlattice (p-SL) on or above the active region, comprising alternating AlGaN and GaN layers;   a p-type GaN layer on or above the p-SL;   a p-type transparent conductive layer on or above the p-type GaN layer;   a p-type pad on or above the p-type transparent conductive layer;   an n-type contact to the n-type GaN layer;   a Zinc Oxide (ZnO) submount attached to the roughened backside of the semipolar GaN substrate;   a header attached to an end of the ZnO submount; and   an encapsulant encapsulating the LED, wherein an active area of the device structure that is an LED is 0.1 mm 2  or less.   
     
     
         15 . The device structure of  claim 1 , further comprising:
 a first III-nitride layer or buffer layer on or above the substrate comprising a GaN substrate;   an n-type superlattice (n-SL) on or above the first layer or buffer layer, wherein:
 the n-SL comprises alternating first and second III-nitride layers having different III-nitride composition, 
 the first and second III-nitride layers comprise strain compensated layers that are lattice matched to the first layer or buffer layer, 
 the first and second III-nitride layers have a thickness that is below their critical thickness for relaxation, 
 a number of periods of the n-SL is such that the active region is separated from the first layer or buffer layer by at least 500 nanometers, and 
 an active region, on or above the n-SL, comprising at least three InGaN quantum wells with GaN barriers, wherein the InGaN quantum wells have a thickness of at least 3 nanometers. 
   
     
     
         16 . The device structure of  claim 1 , wherein the light-emitting device structure:
 has a semi-polar orientation, strain, reduced defects, an alloy uniformity, and an active region comprising a number of indium containing quantum wells forming a semipolar band structure, and   is attached to a mount in a light emitting diode (LED) device,   wherein the mount and the semipolar bandstructure are such that the LED device has the EQE droop of 15% percent or less at the current density of 35 Amps per centimeter square (A/cm 2 ).   
     
     
         17 . The device structure of  claim 1 , wherein:
 the light emitting device structure includes one or more strain compensated layers between an active region and the substrate, and   each of the strain compensated layers have a lattice matching, composition, a thickness below a critical thickness, and a position that engineer strain and defects in the active region wherein the light-emitting device structure has the EQE droop of 15% percent or less.   
     
     
         18 . The device structure of  claim 1 , wherein the III-nitride light-emitting device structure has a semipolar orientation and band structure wherein the light-emitting device structure has the External Quantum Efficiency (EQE) droop of 15% percent or less, as compared to the peak EQE, at the current density of 35 Amps per centimeter square (A/cm 2 ). 
     
     
         19 . The device structure of  claim 1 , further comprising an active area of 0.1 millimeters squared or less. 
     
     
         20 . A method of fabricating an opto-electronic device, comprising:
 growing a III-nitride light emitting device structure on or above a semipolar plane surface of a Group III-nitride substrate and using growth conditions, wherein:   the light-emitting device structure has an External Quantum Efficiency (EQE) droop of 15% percent or less, as compared to a peak EQE, at a current density of 35 Amps per centimeter square (A/cm 2 ).   
     
     
         21 . The method of  claim 20 , wherein:
 the light-emitting device has a light output power in a range of 50-266 milliwatts,   the droop is 0.7-10% at the current density of at 35 A/cm 2 -100 A/cm 2 , and   the light emitting device structure has a peak emission at a blue emission wavelength.   
     
     
         22 . The method of  claim 20 , further comprising:
 mounting the light emitting device structure to a mount, and   electrically contacting the light emitting device structure, including forming transparent contacts,   wherein the light emitting device structure is a light emitting diode structure having an active area of 0.1 millimeters squared or less and grown on the substrate comprising Gallium Nitride (GaN), and   the fabricating, including the growing, mounting, and electrically contacting, fabricates the light emitting diode structure having an External Quantum Efficiency (EQE) droop of 15% percent or less, as compared to a peak EQE, at the current density of 35 Amps per centimeter square (A/cm 2 ).   
     
     
         23 . The method of  claim 20 , wherein the semipolar plane surface is a (20-2-1) plane of a Gallium Nitride substrate. 
     
     
         24 . The method of  claim 20 , further comprising growing an n-type superlattice comprising III-nitride layers and using Si 2 H 6  flow, wherein each of the III-nitride layers is doped with Silicon. 
     
     
         25 . The method of  claim 20 , wherein the substrate is a Gallium Nitride substrate.