Experimental investigation of the kink effect and the low frequency noise properties in pseudomorphic HEMT's

The kink effect in low-noise pseudomorphic (AlGaAs/InGaAs) HEMT's has been examined in detail by investigating the steady-state and pulsed I-V characteristics, the behavior of the output conductance dispersion and the performance of the gate leakage current to understand its origin. No clear evidence of impact ionization occurrence in the InGaAs channel at kink bias conditions (VDS,kink = 1.5 V) has been found, thus suggesting that the predominant mechanism should be attributed to trap-related phenomena. A significant rise of the gate current has been found at very high drain voltages (far from VDS,kink) associated with low drain current values which is probably due to impact ionization onset within the channel. In addition, the low frequency gate and drain noise has been measured at bias conditions below and above the kink to analyze its correlation with the processes involving discrete energy trap states. A Lorentzian noise contribution has been found in the drain noise spectrum traced at kink bias VDS,kink with a corner frequency corresponding to that exhibited by the output conductance dispersion curve at the same bias. Thus, the devices under test classified as short-channel low-voltage GaAsFET's exhibit a marked kink effect whose origin is likely to be due trapping mechanisms.