| The 1990s have brought commercial viability of GaN-based photonic devices and startling progress of GaN-based field effect transistors. However, continued research is required to explore the full potential offered by the III-V nitride system, especially for microelectronic applications and power switches. Further improvement of fabrication procedures is one of high priorities of current research. A host of processing challenges are presented by GaN and related materials because of their wide-bandgap nature and chemical stability. A complete understanding in the critical areas such as ion implantation doping and isolation, rapid thermal annealing, metal contact, and dry etching process, is necessary to improve the routine device reproducibility, and should directly lead to optimization of device performance.;This dissertation has focused on understanding and optimization of several key aspects of GaN device processing. A novel rapid thermal processing up to 1500°C, in conjunction with AlN encapsulation, has been developed. The activation processes of implanted Si or Group VI donors, and common acceptors in GaN by using this ultrahigh temperature annealing, along with its effects on surface degradation, dopant redistribution and damage removal have been examined. 1400°C has proven to be the optimum temperature to achieve high activation efficiency and to repair the ion-induced lattice defects. Ion implantation was also employed to create high resistivity GaN. Damage-related isolation with sheet resistances of 1012 O/□ in n-GaN and 1010 O/□ in p-GaN has been achieved by implant of O and transition metal elements. Effects of surface cleanliness on characteristics of GaN Schottky contacts have been investigated, and the reduction in barrier height was correlated with removing the native oxide that forms an insulating layer on the conventionally-cleaned surface. W alloys have been deposited on Si-implanted samples and Mg-doped epilayers to achieve ohmic contacts with low resistance, and better thermal stability than the existing non-refractory contact schemes. Dry etching damage in GaN has been studied systematically using Schottky diode measurements. Wet chemical etching and thermal annealing processes have been developed to restore the ion-degraded material properties.;Based on these technical improvements, attempts have been made to demonstrate GaN-based bipolar transistors. The devices operated in common base mode at current densities up to 3.6 kA·cm-2 and temperatures up to 300°C. The key issues which currently limit the device performance, such as high base resistance, poor impurity control, and defects resulting from the heteroepitaxial growth, have been addressed. Physically-based simulation suggested that GaN bipolar devices may still suffer from small minority-carrier lifetime in the absence of aforementioned processing problems. |
