The influence of trapped charge on the photovoltaic properties of an efficient Cu2S–CdS single-crystal heterojunction has been studied by a photocapacitance technique. For the non-heat-treated cell, a persistent increment in capacitance as high as 70% of the dark capacitance remained after illumination of the junction by band-gap light at 100°K. The additional capacitance is due to holes trapped in deep levels in the CdS depletion region near the interface. The trapped holes enhanced the 100°K photocurrent spectrum uniformly by a factor of 3 before heat treatment. After a 200°C heat treatment in air, the maximum trapped charge at 100°K enhanced the photocurrent by two orders of magnitude. The results are interpreted in terms of the tunneling through a conduction band spike of electrons photoexcited in the Cu2S. The width of the spike, and thus the tunneling probability, is controlled by the magnitude of the trapped charge. The spike height is estimated to be in the range 13–60 meV.

The 300 °K resistivity and Hall mobility of semi-insulating GaAs can be understood in terms of a model involving four impurity levels, including the deep acceptor Cr and the deep donor O. Neutral impurity scattering is shown to be an important mechanism in this material, and an empirical expression for this component of the mobility is derived. Comparison of mass-spectrographic and Hall-effect data using this model permits the estimation of the electrically active impurity concentrations. Several cases are discussed in which these estimates lead to predictions of surface conversion which agree well with experiment.

The photoelectronic properties of single‐crystal Cu2S‐normalCdS heterojunctions have been investigated. The heterojunctions were formed on the A or Bfaces of conducting normalCdS single crystals by dipping in a cuprous chloride solution at 75°C. No separate heat‐treatment was given. The cells typically had monochromatic quantum efficiencies greater than 10% in the region 0.5–0.9micro;. The photoresponse is due to carrier pair generation in the Cu2S , with transfer of electrons across the interface into the normalCdS . The forward current at and below room temperature is dominated by tunneling of electrons through interface states. A general band diagram of the heterojunction is discussed. Consistent differences in the behavior of A and Bface samples were noted with respect to the growth kinetics of the Cu2S , the maximum photovoltage at 300°K, the I–V characteristics, and the junction capacitance. The effect of uniaxial stress on the capacitance of A and Bface samples suggests a piezoelectric mechanism.

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