Optical Mapping of Local Threshold Voltage With Micrometer Resolution in AlGaN/GaN HEMTs

An electroluminescence (EL) based method is introduced for micrometer-spatial resolution quantitative threshold voltage mapping across transistors, illustrated on GaN HEMTs. The threshold voltage determined using the optical method is confirmed to be consistent with the conventional electrical method that averages a whole device. With this approach, we illustrate spatial variations in threshold voltage along the gate finger width with a spatial resolution of $1~\mu $ m and a voltage resolution of less than 10 mV. Changes in threshold voltage after device stress are shown.