Barrier height diminution in Schottky diodes due to electrostatic screening

Electrostatic screening in the metal contact of a Schottky (metal-semiconductor) diode is shown to influence the calculated electrical characteristics of the diode. A thin space-charge layer is formed at the surface of the metal contact by capacitively induced free charges, This results in a voltage dependent diminution of the barrier height of the diode that increases in magnitude with increasing semiconductor dielectric constant and carrier concentration. Predicted values of the barrier height diminution exceed those attributed to image forces or tunneling effects for materials with dielectric constants greater than about 20. In diodes using semiconducting ferroelectric or piezoelectric materials, an additional diminution of the barrier height results from free charges induced in the metal contact by a remanent polarization field or an externally applied mechanical stress. Current-voltage characteristics of a metal-semiconductor diode are shown to be significantly influenced by the electrostatic screening effect. A soft breakdown current as opposed to saturation current is predicted for reverse biases while an exponential forward current with an η coefficient exceeding unity is predicted for forward biases. Photoemission characteristics are also affected. A voltage-dependent diminution of the threshold energy for photoresponse is predicted. Capacitance-voltage characteristics, on the other hand, differ only slightly from those of an ideal Schottky diode except in the case of a ferroelectric diode where excessively large screening effects are possible.