Copper diffusion into CdS substrates normally occurs in CuxS/CdS solar cells during fabrication, and may cause degradation of solar efficiency because of a decreased proportion of copper in the CuxS. In order to obtain information about deep Cuhyphen;acceptor levels in CuxS/CdS solar cells prepared by both the wet and dry methods on CdS single crystals, an infrared quenching of photocapacitance (PHCAP IR quenching) method has been used. A theory for the description of the PHCAPhyphen;IR quenching, and also for a doping profile by a modified Chyphen;V method using PHCAPhyphen;IR quenching, has been developed to obtain energy levels, photoionization cross sections, and concentration profiles of Cu levels in CdS. Two transitions of 1.08 and 0.86 eV, corresponding to the transition (3d9)Cu2+rarr;(3d10)Cu+, and an internal transition in (3d9)Cu2+, respectively, were measured at room temperature. The photocapacitance quenching level of 0.86 eV disappears at low temperature, and only a 1.20hyphen;eV transition was measured at 91thinsp;K, corresponding to the internal transition (3d9)Cu2+lsqb;E5/2(2T2)rsqb;rarr;(3d9)Cu2+lsqb;G(@qL2E)rsqb;. Spectral distributions of photoionization cross sections sgr;0pvcorresponding to the transition (3d9)Cu2+rarr;(3d10)Cu+were obtained; the peak value was 1.1times;10minus;16cm2. The doping profile of Cu shows that a density of Cu up to one half of the majorityhyphen;carrier density diffused into CdS after heat treatments at 200thinsp;deg;C for a few minutes.
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