Substrate-related kink effects with a strong light-sensitivity in AlGaAs/InGaAs PHEMT

The direct observation of substrate potential (V/sub sub/) changes is experimentally reported, for the first time, on three kinds of kink effects (abrupt increases of drain current) with a strong light-sensitivity in an AlGaAs/InGaAs Pseudomorphic HEMT (PHEMT). The dependence of V/sub sub/ on the kink effects are measured by using a side-gate electrode. The first kink effect is observed with a V/sub sub/ increase from negative to positive value with light. In the dark, with this kink effect eliminated, the second and third kink effects are observed with V/sub sub/ changes at high and low V/sub D/s, respectively. In the second and third kinks, the V/sub sub/s have positive values in all the V/sub D/ region, while there exist two V/sub D/ regions in which logarithmic values of V/sub sub/ remain constant (V/sub sub/ plateaus). Both V/sub sub/s start to increase again near the kink V/sub D/s with different dependences on V/sub G/ reduction by applying further V/sub D/. The mechanisms of the kink effects are discussed based on the behavior of V/sub sub/ and other experimental results, such as photo-sensitivity of the side-gating effect, observation of electron emission in transient waveform, irradiation with a monochromatic light source, and a current DLTS using a sidegate electrode. This work suggests that observation of V/sub sub/ is one of the useful ways to clarify the mechanism of the kink effect.