We observed large enhancement of capacitance with strong voltage sensitivity in InGaN/GaN multiple quantum wells with additional laser illuminations. We have found that the observed negative differential capacitance and its related capacitance peaks in the capacitance-voltage profile are due to the photogenerated charge separation and accumulation at the well/barrier interfaces and its subsequent carrier escape by the applied forward bias. By analyzing temperature dependent photocurrent spectra simultaneously, it is shown that photocarrier separation and strong carrier escape simultaneously occur in an individual quantum well. We can analyze the contribution of a single individual quantum well to the total capacitance of the device, resulting from the nanometer scale carrier separation and accumulation, and clarify the detailed process of accumulation and escape of carriers in the respective quantum wells.
We investigated the heat dissipation in heterostructure field-effect transistors (HFETs) using microRaman measurement of the temperature in active AIGaN/GaN. By varying the gate structure, the heat dissipation through the gate was clearly revealed. The temperature increased to 120 °C
at the flat gate device although the inserted gate increased to only 37 °C. Our results showed that the inserted gate structure reduced the self-heating effect by three times compared to the flat gate structure. Temperature mapping using micro-Raman measurement confirmed that the temperature
of the near gate area was lower than that of the near drain area. This indicated that the inserted gate electrode structure effectively prohibited self-heating effects.
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