OPTICAL, ELECTRICAL, AND PHOTOELECTRICAL PROPERTIES OF SPUTTERED THINAMORPHOUS ZN3P2 FILMS

Amorphous zinc-phosphide films have been prepared by reactive rf sputt ering of zinc in a PH3-containing argon atmosphere. Transmittance and reflectance measurements were used to calculate the refractive index n and the extinction coefficient k as functions of wavelength. The abso rption coefficient a was calculated and an optical gap of 1.60 eV was deduced. The benchmark energy E04, where the absorption reaches 10(4) cm-1, is at 1.75 eV The measurement of the dark conductivity yielded a n activation energy around 0.7 eV, near optical midgap. The magnitude of the pre-exponential factor of the conductivity and the sign of the thermopower indicate that carrier transport is due to conduction in ex tended valence-band states. The photoconductivity is much higher than the dark conductivity at room temperature. A gain of 10(3) was obtaine d by illumination with 100 MW CM-2 white tungsten lamp radiation. From the temperature dependence of the photoconductivity, activation energ ies of 0.18 and 0.3 eV can be deduced.