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WW6.03 - Time-Resolved, In-Situ Cathodomuminescence from GaN Modelled Through a 2D Transistor 
April 24, 2014   8:45am - 9:00am

GaN is of great interest in optical and high power devices. It has a wide, direct band gap, shows strong chemical stability, and can withstand high electric breakdown fields. Innovative technologies aim at ever-smaller devices, with features in the nano-dimensions being achieved. However, devices at the nano-scale are strongly affected by fluctuations promoted by applied fields, trapped internal charges, and surface screening. It is therefore necessary to build a comprehensive model describing charging dynamics to fully understand opto-electronic behaviours typical of in operando GaN.In this work, an in operando device is presented, where a grounded Au-GaN interface is bombarded by an electron beam. In-situ, time-resolved cathodoluminescence (t-CL) and specimen current (SC) have been simultaneously monitored during electron beam irradiation, which promoted distinctive secondary electron contrast from the irradiated regions (SE-IR). Under extreme irradiation conditions the size of SE-IR evolved non-linearly with magnification and increased with irradiation time. Under moderate irradiation conditions, all SE, SC, and t-CL were affected by electron beam parameters environmental exposure. The interplay of all three factors: continuous e-beam irradiation, size (and sign) of SE-IR, and environmental history have been modelled by a 2D transistor to explain SC evolution and SE emission, and to infer mechanisms responsible for near band edge-CL (NBE-CL) degradation upon e-beam bombardment. The proposed 2D transistor explains experimental data (SC and SE-IR) through modifications of Schottky barrier height and depletion width at the Au/GaN interface in the different scenarios. The model also predicts the qualitative behaviour of time constants in NBE-CL. The proposed 2D transistor model aims at providing parameters conducive to optimized operation in GaN devices, where the NBE electron-hole recombination rates are minimally affected by device charge transport and electric field dynamics. This approach will provide an optimized “device by design”, in terms of operation parameters and environmental exposure, crucial towards radiation-hard electronics and microsystems in harsh environments.

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