Impact Ionization Coefficients in Ga2O3

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Nontechnical description: The project is focused on fundamental materials properties of wide bandgap semiconductor, gallium oxide, which shows promise in a range of electrical and optical systems. Since this is a relatively unexplored material, there is a need to establish its basic properties, including parameters that are important for understanding how the material will behave under high electric fields. The research is particularly addressing the impact ionization coefficients, which are currently not established experimentally. The proposed research plan is tackling these parameters at different electric fields and temperatures and is comparing them to the established theory for high voltage behavior in other semiconductor materials. The research, which combines both experimental studies and advanced simulations, is aimed at developing a fundamental understanding of the way in which electrons and holes behave in this promising wide bandgap semiconductor. The role of defects and impurities on the high voltage characteristics of this material impacts a range of technologies including power control electronics in electric vehicles and associated charging infrastructure, ultraviolet emitters and detectors and high frequency/high temperature electronics. The activities provide collaborative research opportunities for a graduate student and several undergraduate students and also engages high school students from underrepresented groups and economically disadvantaged backgrounds.Technical description: The research focuses on fundamental studies of the breakdown mechanism and the role of common defect types and their density on carrier multiplication in gallium oxide. This is a promising material for high power, high temperature systems applications. This proposal will establish basic materials parameters and their electric field and temperature dependence, which are needed to understand the carrier transport and multiplication mechanisms in gallium oxide. The fundamental relations governing the electron and hole transport at high electric fields and over a range of temperatures in gallium oxide needs to be established experimentally. More specifically, the experimental studies focus on examining the temperature dependence of impact ionization coefficients using carrier injection into structures which are biased at a variety of voltages to establish an electric field. The carrier multiplication anticipated under such conditions effect can also be affected by the type and density of defects in the material and this needs to be quantified by examining samples with different defect densities. The research employs electrical characterization techniques, including temperature-dependent current-voltage and diffusion length measurements, with structural analysis using transmission electron microscopy with chemical analysis to provide detailed insights on how defects affect the breakdown characteristics of gallium oxide at high voltages. The experiments are supported by advanced electrical simulations as a function of temperature and voltage, which are used to study the expected influence of these parameters on impact ionization of carriers and transport through the gallium oxide layers. The studies are establishing the transport parameters, which are relevant not only for the basic materials science but also for understanding high temperature operation of gallium oxide based power electronics and solar-blind photodetectors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.