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Hot-electron fluctuation techniques were developed for experimental investigation of picosecond and subpicosecond electronic and phononic processes in voltage-biased 2DEG channels of interest for microwave low-noise and high-power transistors. Examples illustrate real-space transfer, hot-electron energy relaxation, and occupancy relaxation of hot-phonon modes. The pioneering results on hot-electron energy relaxation and hot-phonon lifetime are confirmed by time-resolved response experiments. The fluctuation technique for measuring the hot-phonon lifetime as a function of the hot-phonon temperature is unique, no datum has been reported for comparison as yet.

We present a new semi-insulating GaN buffer layer, which consists of multiple carbon-doped and undoped GaN layers, suitable for AlGaN/AlN/GaN heterojunction field effect transistors. The proposed buffer structure was designed to minimize the total carbon incorporation into the buffer layer because carbon atoms in GaN are a possible cause of deterioration in structural quality and device characteristics such as current collapse. With this new buffer structure, current collapse in GaN MISHFET is drastically reduced while maintaining high breakdown characteristics. We argue that electron transfer from the undoped GaN to the carbon-doped GaN layer leads to total depletion of the undoped GaN layer and effectively compensates the deep-acceptor states in the carbon-doped GaN layer. This mechanism results in high-insulating buffer characteristic and opens the avenue for current collapse suppression in AlGaN/AlN/GaN MISHFET.

We present a new semi-insulating GaN buffer layer, which consists of multiple carbon-doped and undoped GaN layers, suitable for AlGaN/AlN/GaN heterojunction field effect transistors. The proposed buffer structure was designed to minimize the total carbon incorporation into the buffer layer because carbon atoms in GaN are a possible cause of deterioration in structural quality and device characteristics such as current collapse. With this new buffer structure, current collapse in GaN MISHFET is drastically reduced while maintaining high breakdown characteristics. We argue that electron transfer from the undoped GaN to the carbon-doped GaN layer leads to total depletion of the undoped GaN layer and effectively compensates the deep-acceptor states in the carbon-doped GaN layer. This mechanism results in high-insulating buffer characteristic and opens the avenue for current collapse suppression in AlGaN/AlN/GaN MISHFET.