CURRENT TRANSPORT IN PD-SIO2-N(P)-SI MIS STRUCTURES AND A 2ND MECHANISM FOR PHOTOCURRENT AMPLIFICATION

Current-voltage characteristics and the photocurrent have been studied as a function of the reverse bias voltage. The decay kinetics of the reverse current in Pd-SiO2-n(p)-Si MIS structures with a thick SiO2 la yer (on the order of 1000 Angstrom) has also been studied. At high inj ection levels, the current transport is determined by a space-charge-l imited current, and the overall current-voltage characteristic in the forward direction can be described by I = alpha(1) V + alpha(2) V-3. T he kinetics of the decay of the reverse current has a dispersion shape , I similar to t(-(1-a)), where alpha = 0.75. It is stretched out alon g the time axis by a factor of more than 2.5 orders of magnitude. It i s explained in terms of stochastic trapping and liberation of carriers . An amplification of the photocurrent is observed at a reverse bias v oltage. This amplification is explained in terms of an exponential inc rease in the lifetime of carriers of one type (electrons) because of a trapping of exponentially distributed trapping centers for carriers o f the other type. No effect of a gaseous medium containing hydrogen du ring the fabrication of the structures on the photocurrent or dark cur rent was observed. This result confirms that bulk processes have a dec isive effect on the current transport. (C) 1995 American Institute of Physics.