OFF-State Leakage and Current Collapse in AlGaN/GaN HEMTs: A Virtual Gate Induced by Dislocations

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The existence of a correlation between current collapse and off-state reverse-bias leakage current in heteroepitaxially grown AlGaN/GaN high-electron-mobility transistors is investigated from the perspective of conductive threading dislocations. Collapsed current response (recoverable) to synchronized gate-drain voltage pulses is found to be governed by the epilayer's dislocation density, and also by the off-state quiescent bias scheme. Furthermore, magnitudes of reverse-gate leakages apart from being dislocation density dependent are found to have distinctive temperature-bias characteristics. Based on the trapping spatiality along with field and temperature dependence of the respective leakage currents; an emission mechanism is postulated involving donor-like surface states and dislocation induced deep levels. It is inferred that dislocations can indeed be responsible for the current collapse that has been long assumed to be caused by the surface states.