Transduction characterization of robust Wurtzite wide-bandgap semiconductor devices under irradiation
Keywords: Materials Science and Engineering.

Radiation-induced failure of electronic devices is one of the most significant barriers to human exploration of space. In order to successfully operate in these radiation-rich environments, it is necessary that we consider moving to new materials systems and device architectures that can inherently resist ionizing radiation-induced degradation. This dissertation presents results of the fabrication and testing of several different device architectures fabricated using wide-bandgap wurtzite-structured semiconductor materials that are known to be radiation-hard and that have been subjected to different types of ionizing radiation. The first two chapters of this dissertation discuss the need for radiation-hard electronics, examine the state-of-the-art for radiation hardening of electronics, discuss common types of radiation, their effects on materials, and the environments in which they are typically found, and explain the comparative advantages of wide-bandgap semiconductor materials vs conventional semiconductors for use in environments rich in ionizing radiation. Next, a growth process for indium aluminum nitride/gallium nitride (InAlN/GaN) thin-film heterostructures is demonstrated. Advantages relative to more developed aluminum gallium nitride/gallium nitride (Al-GaN/GaN) heterostructures are explained, fabrication challenges and solutions are discussed, and Scanning Electron Microscopy (SEM), x-ray diffraction (XRD) and Hall effect measurements are used to qualitatively and quantitatively compare the quality of films produced with different growth conditions. Then, design, fabrication, and testing of GaN-on-Silicon betavoltaic energy harvesters is presented. These devices were fabricated using a triple mesa etch technique and tested under irradiation by an electron beam tuned to simulate the beta emission spectrum of 63Ni, in lieu of the isotope itself. These results represent, at time of publication and to the best of the author's knowledge, the highest recorded experimentally-measured efficiency for a GaN-based betavoltaic device. Afterwards, design and testing of thin-film zinc oxide (ZnO) semiconductor-on-insulator (SOI) metal-semiconductor-metal (MSM) ultraviolet photodetectors is discussed. The ZnO films were grown on an insulating silicon dioxide (SiO2) substrate using atomic layer deposition, fabricated into devices, and subjected to proton irradiation while held at temperatures ranging from -25°C to 70°C. UV photocurrent transient measurements were taken using a 365 nm LED. The resulting data were then fit to a stretched exponential function to find decay time constants, which were then used with an Arrhenius equation to extract defect activation energies. These energies were then compared to known values from literature to tentatively identify the defects resulting from different irradiation conditions. It was determined that even small changes in temperature produced noticeable, long-term changes in resulting defect structures that affected device performance even months after irradiation. This dissertation concludes by proposing several avenues for potential future work, including optimization of film growth and device design, testing of both the betavoltaic devices and the UV photodetectors in real radiation environments, and development of specialized gettering techniques to help prevent the accumulation of radiation-induced point defects, reducing their detrimental effect on device performance