GaN Electronics For High Power, High Temperature Application

The commercialization of blue, green and white GaN-based light-emitting diodes and violet laser diodes has created tremendous interest both from an applications viewpoint and for the basic science of the AlGaInN materials system. The fact that extremely efficient light emission can be achieved in heteroepitaxial layers of these materials grown on lattice mismatched substrates such as sapphire is counter to the experience of almost 40 years of semiconductor light source technology. The high dislocation density in these heteroepitaxial layers (sup (10) - 10 sup (11) cm sup (-2)) is clearly not as deleterious as in more conventional materials systems such as GaAs/AlGaAs, InP/InGaAsP and GaAsP/GaP. While large diameter GaN bulk substrates are nor commerically available and will not be in the foreseeable future, ingenious methods of creating quasi-substrates have been developed. These include lateral overgrowth of GaN on dielectric-patterned sapphire of SiC substrates, in which the growth of GaN up and over the dielectric pattern creates regions of much lower dislocation density, or growth of thick (100microns) GaN epitaxial layers on mismatched substrates, followed by separation from the substrate to create a free-standing GaN substrate. Photonic devices fabricated on these lower-defect GaN regions have even better optical output and reliability than those fabricated on highly defective regions.