MIS Diode Structure in As⁺ Implanted CdS

Abstract

Clear evidence demonstrates that a prominent rectification behavior observed in current-voltage characteristics for As implanted and annealed, high-conductivity CdS exposed to sub-band-gap illumination is due to a metal-semiconductor junction in a platinum electrode-implanted layer interface. A typical illuminated device has a forward turnover voltage of 1.15 volts and a reverse breakdown voltage of 25–30 volts. Platinum barrier diodes fabricated in identical fashion on an unimplanted half of the substrate also display rectification behavior when exposed to sub-band-gap illumination, although the forward turnover voltage is only 0.65 volts. Placed in the dark, both diodes remain rectifying although their forward turnover voltages increase to 14 volts for the unimplanted (U) diode and 18 volts for the implanted (I) diode. Dominance of a rectifying barrier between the Pt electrodes and the implanted layer is demonstrated by over-coating a Pt contact with a liquid mixture of Ga and In, letting some of the metal contact the implanted layer surface. The Ga/In contact almost eliminates the rectifying nature of the contact, and yields a nearly linear current-voltage characteristic.