Electrical mitigation of radiation-induced defects in AlGaN/GaN photovoltaic detectors

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Non-technical: Ultraviolet photodetectors have many uses, such as chemical and biological analysis or flame detection. Damage by energetic particles degrades the sensitivity of ultraviolet photodetectors in harsh radiation environments. This project will lead to a dramatic increase in the recovery of photodetectors based on gallium nitride (GaN). This outcome will be achieved by electrical tailoring of a fundamental property of GaN, the electron diffusion length, by in-situ charge injection under applied voltage. Photodetector sensitivity will recover completely and return to the original state prior to irradiation. The project will advance the fundamental understanding of the nature of point and extended defects in GaN-based semiconductors and devices. The project will integrate research and education at the graduate and undergraduate levels and features an active industrial partner.Technical: This project focuses on electrical mitigation of irradiation-induced defects by charge injection into ultraviolet photodetectors based on gallium nitride (GaN). The ultimate aim is to produce radiation hard and efficient devices. This project hinges on the PI's previous findings that charge injection into p-type GaN leads to considerable changes in the material's electronic properties, particularly the carrier diffusion length. These changes result in an order of magnitude enhancement of the photodetector quantum efficiency. It is therefore possible to improve performance of photodetectors, affected by radiation, using short pulses of solid-state forward-bias charge injection into GaN p-i-n devices. The project will lead to a better understanding of the interaction between wide gap semiconductors and highly energetic particles, including electrons, gamma-ray photons, and protons, as well as of the nature of radiation-induced defects. Charge injection will result in enhanced minority electron diffusion length in the top p-type absorption layer of a photodetector, thus increasing the quantum efficiency for the device and "healing" the adverse impact of gamma-rays, protons, electrons and other radiation types. A unique combination of electrical, optical and structural studies in the PI's lab will shed light on the mechanism, which is responsible for the effect of interest. Studies of minority carrier diffusion length and lifetime will be carried out in independent experiments using electron beam-induced current and ultrafast time-resolved cathodoluminescence at various temperatures. Polychromatic continuous-wave cathodoluminescence will be employed for assessment of irradiation impact on threading dislocation density in GaN. Finally, deep level transient spectroscopy will allow studies of radiation-induced point defects. The ultimate goal is to correlate charge injection regimes (current; voltage; duration) and irradiation doses, thus proceeding towards control of photodetector performance and recovery from radiation damage by purely electrical means.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.