| The III-V nitrides have proved to be good materials for optoelectronic and electronic devices due to their large bandgaps, high breakdown voltages, and high carrier velocities. To further improve the device performance for outdoor lighting and wireless communication, it is essential that ohmic contacts with very low contact resistance be developed. The selective area growth (SAG) utilizing tunneling effect has been the most promising approach to obtaining the desired low resistance. However, there have been a number of problems, such as the desorption of GaN and diffusion of dopants.;The main objective of this research is to investigate and develop stable and reproducible low ohmic contacts through careful monitoring of the GaN surface and distribution of dopants while employing SAG by plasma assisted molecular beam epitaxy (PAMBE). The work specifically involved thin film growth, film characterization, device fabrication and device characterization. To develop the SAG technique and study the effect of etchants on single crystal GaN layers during ohmic contact fabrication, surface bonding and surface morphology were examined. Another important phase of this work consisted of achieving the ohmic contact and device performance enhancement with SAG process and interface analysis by cross sectional TEM. The SAG technique was expanded to nonalloyed ohmic contacts proving that the SAG is crucial in fabrication of nonalloyed ohmic contacts. Finally, high electron mobility transistors (HEMTs) were demonstrated for a realistic DC-DC (direct current) converter. |
