Ultraviolet Solar Blind Ga2O3-Based Photodetectors

Detection within the deep ultraviolet (DUV) region (˜200-280 nm) offers unique fundamental advantages to probe certain optical traces. Therefore, many applications have emerged including flame and missile detection, and non-line of sight and space-to-space communication. Ga2O3 has become a natural choice for DUV detection owing to its intrinsic ultra-wide optical bandgap (˜4.85 eV), extrinsic n-type dopability, and excellent chemical and physical stability. However, Ga2O3 has no viable p-type doping to date, and fabricated photodetectors show only partial coverage of the entire solar-blind region (˜200-245nm). Furthermore, there is a limited understanding of how various growth parameters for ß-Ga2O3 and its alloys impact the material properties (i.e. defects), and how these ultimately play a role in functional device characteristics. This dissertation aims to address the aforementioned challenges with systematic studies spanning across epitaxial growth by molecular beam epitaxy (MBE), device fabrication, and characterization, leading to a comprehensive understanding of how these impact the optical, structural, compositional, and device properties. The experiments start with homoepitaxial and heteroepitaxial growth of Ga2O3 on bulk n-Ga2O3, sapphire, and advance to the growth on Si by MBE for monolithic integration. A novel nucleation technique of Ga2O3 on n-Si substrate allowed achieving one of the fastest functional DUV photodetectors with high responsivities. Furthermore, bandgap engineering via alloying Ga2O3 with In and Sn improved the DUV coverage, extending the cut-off wavelength beyond ˜245 nm, while benefitting higher responsivities. A record-setting photoresponsivity (˜35 kA/W) among planar devices was achieved with Sn alloying. The mechanisms leading to the unusually high photoconductive gains in these devices were investigated to determine the root cause. Point defects, particularly gallium vacancy-related complexes, are identified as the most likely source of ultra-high gains by hole-trapping at space-charge-region of Schottky barrier photodetectors. Moreover, a direct trade-off between bandwidth and responsivity was observed due to these complexes