Characterization of phototransistor internal gain in metamorphic high-electron-mobility transistors

The phototransistor internal gain in metamorphic high-electron-mobility transistors (mHEMT) was analyzed. The phototransistor internal gain was determined by estimating the primary photocurrents that were due to absorbed optical power from the device when it acted as a photodetector. It was observed that the dominant photodetection mechanism was the photocunductive effect when the device was turn-off and photovoltaic effect when the device was turned-on. It was observed that the phototransistor internal gain was represented by the ratio between the photodetected power and absorbed optical power due to the photovoltaic effects.