Cryogenic Kink Effect in InP pHEMTs: A Pulsed Measurements Study

We present a study based on pulsed measurement results of the kink effect observed on the I-V output characteristics in InGaAs/InAlAs/InP pseudomorphic high-electron mobility transistors (InP pHEMTs) at cryogenic temperatures. Pulsed measurements were performed at 300 and 10 K. Gate and drain lags were observed at both temperatures with a strong increase upon cooling for the drain lag. To study the influence of surface traps in the kink, pulsed measurements of devices passivated by either atomic layer deposited Al2O3 or plasma enhanced chemical vapor deposited Si3N4 were compared with no significant differences at 10 K. The influence on the kink effect from the buffer was studied by comparing pulsed measurement data from an InP pHEMT with measurements on a GaAs metamorphic HEMT (GaAs mHEMT). For the GaAs mHEMT, an increase of the drain lag at 10 K was observed when compared with the InP pHEMT. Contrary to the InP HEMT, for the GaAs mHEMT the 0.1 mu s pulses were short enough to eliminate the kink when using a quiescent point with V-DS = 0. The quality of the pinchoff was sensitive to pulse length and quiescent point for the InP pHEMT but not for the GaAs mHEMT.