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CuS and Sb2S3-CuS has shown the formation of films of ternary composition, Cu 3BiS 3 [5] and Cu 3SbS 4 [6], respectively. Thermal treatments of evaporated indium film on II-VI semiconductors in turn resulted in heierostructures of the type, MX:In-In 20 3 [7-9]. In this paper we report, for the first time, the formation of InSb thin film through a solid state reaction of evaporated indium film on a chemically deposited Sb2S3 . The reaction takes place in a nitrogen atmosphere at 300°C.The properties of the films and the mechanism of formation of the IlI-V compound from V2-V1 3-IHI stack are discussed. EXPERIMENTAL Deposition of thin films Antimony sulfide thin films were deposited using a chemical bath reported in a previous work [6]. Microscope glass slides were used as substrates. These substrates were cleaned using commercial detergent and deionized water and dried in air. The bath was prepared in a 200 ml beaker as follows: 1.3 g of SbCi 3 (Baker Analyzed Reagent) was dissolved in 5 ml of acetone. To this was added 50 ml of I M Na 2S20 3 (Reactivo Analitico Monterrey) that was previously cooled to 10'C, followed by the addition of 145 ml of cold deionized water and stirred well. The substrates were placed in the bath, vertically supported on the wall of the beaker. The deposition was made at 100 C. At the end of 4 h of deposition, glass slides covered with specularly reflective 169

Mat. Res. Soc. Symp. Proc. Vol. 573 ©1999 Materials Research Society

orange-yellow thin films of Sb 2S3 were removed from the bath, washed well with deionized water and dried. Step-thickness measurements using an Alpha Step 100 unit showed that the film thickness was about 0.2 Atm. By immersing these films in a second bath, film thickness of 0.3 Am or more could be obtained. Thin films of indium were deposited on the Sb 2S3 thin films by thermal evaporation of 20-60 mg of 99.999% In (Alfa Products) in a high-vacuum coating unit after attaining a residual pressure of 10.6 mbar. Since the films of indium are very soft, step thickness measurement was not possible. Thus the thickness of In film deposited on the slides was estimated gravimetrically: approximately 0.075 ý.m of In film was deposited on an Sb 2S 3 coated substrate for an indium source of 20 mg. The Sb 2S3-In films were annealed for I h each in a vacuum oven (T. M. Vacuum Products Inc., New Jersey) in 50 m Torr of nitrogen. Characterization X-ray diffraction (XRD) patters were recorded using Cu-Ke radiation on a Siemens D500 diffractometer. The optical transmittance (T%) and the near-normal specular reflectance spectra (R%) of the films were recorded on a Shimadzu UV-3101PC UV-VIS-NIR scanning spectrophotometer with air and a front aluminized mirror, respectively, as references. For the electrical measurements, silver paint electrodes were printed on the samples in a coplanar configuration. The dark- and the photo- currents were recorded on a computarized system using a Keithley 619 electrometer and a Keithley 230 programmable voltage source. Photocurrent response measureme