| III-V nitrides have been investigated intensively due to the enormous interest in optoelectronic device applications in the green, blue, violet, and near-ultraviolet regions. Advances in III-V nitride materials for short wavelength light sources will lead to both a revolution in optical disk storage, as higher densities can be achieved with short wavelengths, and a major impact on imaging and graphic technology as high quality red, green, and blue light-emitting diodes (LED) and lasers become available. High quality GaN films have mostly been prepared by metal-organic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE) and vapor phase epitaxy (VPE). Compared to these techniques, pulsed laser deposition (PLD) is a relatively new growth technique used widely for the growth of oxide thin films. However, several advantages of PLD make it worthy of study as a method of growing nitrides. The congruent ablation achieved with short UV-laser pulses allows deposition of a multicomponent material by employing a single target and the ability for depositing a wide variety of materials. This advantage makes PLD very suitable for growing multilayer structures sequentially in the same chamber and investigating the effect of buffer layers. Moreover, the strong nonequilibrium growth conditions of PLD may lead to different nucleation and growth processes.; In this work, GaN and (Al,Ga)N films have been epitaxially grown on (0001) sapphire substrate by PLD, which has been successfully applied to controlling the lattice constant and band gap of (Al,Ga)N. Room-temperature photoluminescence of PLD-GaN exhibits a strong band edge emission at 3.4eV. The threading dislocations of GaN are predominantly screw dislocations with Burgers vector of <0001> while edge dislocations with Burgers vector of 1/3<11-20> are the dominant ones in GaN grown by MBE, MOCVD and VPE. This variation observed in defect characteristics may come from the difference in nucleation and growth kinetics between PLD and other deposition techniques. In addition, epitaxial ZnO buffer layers with better crystalline structure and surface flatness have been developed by PLD for GaN epitaxy. The effects of ZnO buffer on GaN grown by both PLD and VPE were studied. |
