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

The direct observation of substrate potential (V_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 on the kink effects are measured by using a side-gate electrode. The first kink effect is observed with a V_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 changes at high and low V_Ds, respectively. In the second and third kinks, the V_subs have positive values in all the V_D region, while there exist two V_D regions in which logarithmic values of V_sub remain constant (V_sub plateaus). Both V _subs start to increase again near the kink V_Ds with different dependences on V_G reduction by applying further V_D. The mechanisms of the kink effects are discussed based on the behavior of V_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 is one of the useful ways to clarify the mechanism of the kink effect