Phototransistor measurements in AlGaN/GaN HBTs

A fast and reliable method for evaluation of transistor gain in npn AlGaN/G aN heterojunction bipolar transistors is demonstrated. The method is based on phototransistor measurements. which are carried out in situ in a scannin g electron microscope. Electron beam current was used in these measurements as an analogue of current in the base, which remained floating. The obtain ed common-emitter DC current gain, beta, is similar to2.5, This value is in good agreement with the values of beta obtained from the conventional thre e-terminal measurements.