Light-emitting Diodes Based on Epitaxy on Non-polar Sidewalls and III-Nitrides Nanowires

Light emitting diodes (LEDs) grown on the etched non-polar plane sidewall stripes of polar c-plane GaN/sapphire templates by metal organic chemical vapor deposition (MOCVD) demonstrated that sidewall epitaxy significantly reduces the quantum confined Stark Effect found in quantum wells (QWs) grown on c-plane substrates. Preferential semi-/nonpolar crystallographic plane formation during LED structure depositions on etched sidewall stripes, propagation of dislocations during sidewall epitaxy and effect of n-/p-type doping on growth mechanisms together with incorporation of indium on sidewalls were studied.;Epitaxial growth of GaN films on GaN nanowires (NWs) lead to the development of an embedded void approach (EVA) technique for defect reduction in GaN epitaxial films grown on sapphire substrates. GaN NWs were created by the mask-less dry etching technique. The etched, then annealed, NWs form semi-polar and non-polar plane facets with hexagonal symmetry. The different growth rates on the different plane facets results in forming void networks. This technique relies on the generation of high densities of embedded micro-voids (∼10 8/cm2), a few microns long and less than a micron in diameter. These voids are located near the sapphire substrate, where high densities of dislocations are present. A network of embedded voids offers free surfaces that act as dislocation sinks or termination sites for the dislocations generated at the GaN/sapphire interface. Results confirm the uniform reduction of the dislocation density over large area substrates by approximately three orders of magnitude and a lower surface roughness than the GaN starting material.;A light-emitting diode (LED) structure with multiple quantum wells (MQWs) conformally grown on semipolar and nonpolar plane facets of n-GaN nanowires (NWs), followed by deposition of fully coalesced p-GaN on these NWs was demonstrated as an another application of the EVA technique. Overgrowth on the NWs. tips results in inclusion of high density voids, about one micron in height, in the GaN film. The light output intensity of NWs LEDs is more than three times greater than corresponding c-plane LEDs grown simultaneously. We believe this results from a reduced defect density, increased effective area of conformally grown MQWs, absence of polar plane orientation, and improved light extraction.;Most device structures are based on epitaxial growth of lattice matched thin films. In lattice mismatched systems, there is a critical layer thickness, hc, below which the epitaxial layer is strained and the strain is generally being shared by the film and the substrate. The value of hc can be a few nanometers for systems with lattice mismatch of a few percent. For thickness t > hc, misfit dislocations appear at the interface. Embedded void approach elevates the restriction and eliminates the problems encountered during the growth in lattice mismatched systems.