CuxZnyS films with low Cu content were deposited by photochemical deposition, and the relation between conduction type and Cu content was investigated. The deposition solution for CuxZnyS was similar to that for ZnS (1 mM ZnSO4, 600 mM Na2S2O3, and 3 mM Na2SO3), with the addition of CuSO4. The substrate was held 2-3 mm below the solution surface and irradiated with an Hg-arc lamp. The films were transparent in the visible range and had a band gap of about 3.6-3.8 eV. The composition was evaluated by Auger electron spectroscopy (AES), and the conduction type was determined by photoelectrochemical (PEC) measurements. Clear p-type signals were observed in the PEC measurements for CuSO4 concentrations higher than 0.3 mM, whereas n-type conduction was observed for CuSO4 concentrations lower than 0.05 mM. The critical Cu content in the film at the transition of the conduction type was below the detection limit of AES and thus was estimated by extrapolating the results for higher CuSO4 concentrations. We estimated that the conduction type changed around a Cu content of 0.5%-1% in this alloy system. (C) 2015 Elsevier B.V. All rights reserved.