Time dependence of depletion region formation in phosphorus-doped silicon MOS devices at cryogenic temperatures

The time dependence of depletion region formation in 1015/cm3 phosphorus-doped silicon MOS devices in the temperature range 14–25 °K has been observed using three different experiments: fast ramp C-V measurements, pulsed capacitor measurements, and pulsed transistor measurements. It is observed that the time required to form a depletion region in thermal equilibrium is strongly dependent on the applied gate bias. Following the application of a gate bias from accumulation to deep depletion, a peak is observed in the substrate current versus time. These results are explained by the dependence of the electron-emission rate from the phosphorus donors on the electric field in the semiconductor (Poole-Frenkel effect). Calculations from a one-dimensional model including the field emission effect are shown to predict the major features of the data.