MINORITY-CARRIER MIS TUNNEL-DIODE HYDROGEN SENSORS

The electrical characteristics of Pd/LB film/n-Si tunnel diode hydroge n sensors containing one and three cadmium stearate Langmuir-Blodgett (LB) films are reported. The devices exhibit good rectification behavi our, However, the IV characteristics are complex and deviate considera bly from ideal Schottky-barrier theory. The semiconductor surface appe ars to be inverted at zero bias. Saturation of the forward current is attributed to tunnel-limited transport in the case of single LB film d evices and to insulator-limited conduction in the case of devices cont aining three LB films. Exposure to hydrogen causes pronounced degradat ion of the diode behaviour. In particular, the forward IV characterist ic shows an Ice V-2 behaviour that cannot be satisfactorily explained. A plausible explanation, however, is offered for much of the observed data based upon a minority-carrier metal-insulator-semiconductor (MIS ) tunnel diode model. However, the full range of behaviour observed ca nnot be treated adequately by any one theoretical model.