Lateral Charge Transport in the Carbon-Doped Buffer in AlGaN/GaN-on-Si HEMTs

Abstract

Dynamic $\text {R}_{\mathrm{\scriptscriptstyle ON}}$ and ramped substrate bias measurements are used to demonstrate size- and geometry-dependent dispersion in power transistors. This is due to a novel lateral transport mechanism in the semi-insulating carbon-doped GaN buffer in AlGaN/GaN high-electron-mobility transistors. We propose that the vertical field generates a 2-D hole gas (2DHG) at the bottom of the GaN:C layer, with hole flow extending outside the isolated area. The device-to-device variation is due to a combination of widely spaced preferential leakage paths through the structure and lateral transport from those paths to trapping sites. The spread of the 2DHG outside the active area of the device strongly affects the result of substrate ramp measurements producing major differences between single and multifinger devices. In dynamic $\text {R}_{\mathrm{\scriptscriptstyle ON}}$ recovery measurements, single-finger devices show large device-to-device variation, with multifinger devices showing a small variation with the transient comprising the superposition of the recovery transient of multiple small single-finger devices.