Growth, characterization and processing of gallium nitride films for high temperature electronics and optoelectronics in blue to UV.

摘要

GaN thin films were grown on (001) GaAs substrates by ECR plasma assisted MBE to study defects. The growth rate of GaN is only about {dollar}sim{dollar}0.2 {dollar}mu{dollar}m/hr. Due to large lattice and thermal mismatches between GaAs and GaN, the crystalline quality of GaN films is not adequate for electronic or photonic devices. In spite of the cubic symmetry of the substrate, wurtzite structure GaN films grow in a columnar structure and each column is oriented along the c-axis. Several in-plane orientations are observed in the GaN films from X-ray diffraction {dollar}phi{dollar}-scan. While photoluminescence (PL) spectra at 77K show strong band edge related emission at 3.47 eV, they also contain broad defect-impurity related emission around 2.1 eV.; Bulk GaN can only be grown at extremely high pressures. The much faster growth rate with good crystalline quality of hydride vapor phase epitaxy (HVPE) makes it one of the best approaches to grow pseudo-bulk thick GaN films. These films will be used as the substrates for homoepitaxial growth of subsequent device structures grown by MBE or MOCVD. A new HVPE system, which uses crystalline GaCl{dollar}sb3{dollar} and NH{dollar}sb3{dollar}, as the group III and V sources, respectively, was developed. Thermodynamic calculations were carried out. Growth parameters were optimized in order to obtain high crystalline quality thick GaN films with smooth surfaces. (0001) and (1120) oriented Al{dollar}sb2{dollar}O{dollar}sb3{dollar} wafers are used as substrates. The GaN films are single crystalline. A high density of defects, such as dislocations and stacking faults, are observed near the interface and their density decreases drastically with an increase of film thickness. GaN films show very sharp, strong band edge related photoluminescence without any obvious defect related emission. AlN buffer layers were deposited by RF sputtering. Crystalline quality and surface morphology of GaN films grown on AlN buffer layers are greatly improved. The minimum RBS channeling yield and FWHM of X-ray rocking curves of GaN films grown with thin AlN buffer layers are smaller than those of GaN films grown directly on Al{dollar}sb2{dollar}O{dollar}sb3{dollar} substrates.; GaN films were successfully patterned by reactive ion etching (RIE) using Cl (H) containing plasmas. SiCl{dollar}sb4{dollar} and CHCl{dollar}sb3{dollar} plasmas etch GaN much faster, up to 4{dollar}sim{dollar}5 times, than CHF{dollar}sb3{dollar} and C{dollar}sb2{dollar}ClF{dollar}sb5{dollar} plasmas under identical etching conditions. Higher crystalline quality GaN films exhibit slower etch rates than defective GaN films. AFM measurements demonstrate that reactive ion etching does not cause any serious surface roughening and the surface becomes smoother after etching due to faster etching of the peaks of the film. XPS analysis reveals that the etched surfaces are slightly contaminated by carbon and oxygen. Serious photoresist mask erosion and hardening are often observed. Therefore, fine pattern transferring to GaN films using photoresist mask and complete removal of remaining photoresist after etching is very difficult. By replacing the etch mask from conventional photoresist to sputtered iron nitride film, GaN films can be finely patterned with vertical etched sidewalls. (Abstract shortened by UMI.)