Coupled surface and channel transport in semiconductor heterostructures

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Abstract
Electron transport in a channel separated from the surface by a thin insulating barrier layer is shown to be profoundly affected by electrical conditions on the surface. Nonuniformities in the coupled surface and channel systems lead to depletion and accumulation regions in the channel and the depletion regions can cause the current to saturate at unusually low voltages. Even when there are no nonuniformities it is shown that the coupled system exhibits a density instability that leads to similar phenomena. These effects are described in terms of an analytical model that takes into account diffusion and hot-electron transport applied to the AlGaN/GaN system. It is noted that the effect of any extension of the channel under the cathode (source) can produce depletion and current saturation that can be mistaken for the result of a nonohmic contact resistance.