Phototransistor measurements in AlGaN/GaN HBTs

Abstract
A fast and reliable method for evaluation of transistor gain in npn AlGaN/GaN heterojunction bipolar transistors is demonstrated. The method is based on phototransistor measurements, which are carried out in situ in a scanning electron microscope. Electron beam current was used in these measurements as an analogue of current in the base, which remained floating. The obtained common-emitter DC current gain, β, is ~2.5. This value is in good agreement with the values of β obtained from the conventional three-terminal measurements.