Anomalous effects on the current-voltage characteristics of p-channel metal-oxide-semiconductor transistors in the temperature range 4.2–50 K

Abstract

The current-voltage characteristics of p-channel MOSFETs (metal-oxide-semiconductor field-effect transistors) in the temperature range 4.2-50 K have been investigated in detail. A peak is observed at the beginning of the drain-current–drain-voltage (Id, Vd) curves for low Vg values, which is not observed in the case of n-channel MOSFETs and is found to be a very slow transient effect. This time-dependent peak is observed for temperatures below ∼25 K and for channel lengths greater than ∼3 μm. In this temperature range a strong hysteresis effect is also observed at low Vg voltages. The above behavior will be explained in terms of a very slow depletion layer formation in the drain region, introduced by the large time constant of the field-assisted thermal emission of carriers in n-type bulk semiconductors at temperatures below ∼20 K. Another effect, analogous to the ‘‘kink effect’’ observed in n-channel MOSFETs at temperatures below 16 K, is also observed for low Vg and Vd values. This effect is observed with difficulty and is less pronounced than in n-channel MOSFETs.