Photodetection by light-induced barrier modulation in Cu-diffused Au–CdS diodes

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Abstract
Modified Schottky barriers of the type Au–CdS : Cu were prepared by diffusing Cu to a depth of 0.1–0.2 μm into single crystals of CdS, prior to evaporating rectifying Au contacts. The electronic and photoelectronic properties of these junctions are adequately described by a simple model in which the Cu acts as an ionized acceptor, resulting in a ``humped'' potential barrier between the Au and the bulk CdS. Hole trapping by the acceptors under band‐gap illumination reduces their ionization and, consequently, the hump height. The forward current density in the dark and under illumination can be accurately described by a thermionic emission model as J=A*T2 exp {—e[VB+VH(0)]/kT exp}(eV/βkT), where the hump potential VH (0) is light sensitive and where β (1<βJ‐V measurements unequivocally show that under saturating light conditions the hump in the potential barrier is reduced by 0.23±0.03 V. This barrier mechanism of photoconductive response results in steady‐state electron/photon gains in excess of 106 at light intensities lower that 5×1011 photons cm−2 sec−1, where response times exceed 1 sec.

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