CdS thin films deposited from chemical bath containing citratocadmium(II) and thiourea are intrinsic and highly photosensitive. In the present letter, we discuss the conversion of such films to n type by thermal diffusion of indium from an evaporated 50 nm indium film deposited on the CdS thin film. The process which takes place in the temperature range of 250 °C–350 °C involves the formation of an In2O3 surface layer which acts as a barrier preventing the outdiffusion of indium. This allows indium to diffuse into the CdS film and results in an indium-doped CdS thin film. The electrical conductivity of such films is about 300 Ω−1 cm−1. All beneficial optical properties of chemically deposited CdS thin films for application as a window material in heterojunction optoelectronic devices are retained.

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Conversion of chemically deposited intrinsic CdSe thin films to n-type coatings by a postdeposition process is described. A Cd:Se-In thin film consisting of a CdSe thin film -0.15 p.m thick and a thermally evaporated indium film -0.02 p.m thick was air annealed at 325°C for 1 h. The resulting thin film coating of CdSe:In (0.15 p.m)-1n20,(0.03 p.m) exhibits a sheet resistance of 790 11/0 and an n-type conductivity of -400 fl' cm-' for the In,O, top layer. Etching of the film with 1 M HC1 for 6 h removes the superficial 1n203 from the coating, and the underlying CdSe with indium doping shows a sheet resistance of 15 kIll/fl which corresponds to electrical conductivity (n-type) of -0.4 fl' cm'. The composition of the film and its variation along the depth are established through analyses of x-ray diffraction pattern and xray fluorescence spectra as well as the photocurrent response of the annealed films recorded before and after chemical etching. InfroductionThe chemical bath deposition technique is a simple method for growing adherent, uniform, and specularly reflecting thin films, particularly of Il-VI semiconductors.' This technique has been used to deposit CdSe thin films from solutions containing a cadmium ion complex and either selenosulfate,2'3 (Na,SeSO,); selenourea , (NH2),CSe; or N,N-dimethylselenourea,' (C,H,N,Se); as the source of selenide. After an initial nucleation phase, ion-by-ion con-

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