Preparation and characterization of HgS ®lms by chemical deposition S.S. Kale, C.D. Lokhande * Thin Film Physics Laboratory, Department of Physics, Shivaji University, Kolhapur 416004, India Received 30 October 1998; received in revised form 12 January 1999; accepted 19 January 1999 Abstract Effect of preparative parameters on the properties of chemically deposited HgS ®lms is reported. The effect of ®lm thickness on the optical, structural and electrical properties was studied. The shift of 0.45 eV in the optical band gap energy, E g , and an increase in electrical resistivity from 10 3 to 10 4  cm and decrease in grain size of HgS crystallites from 80 to 30 A Ê were observed when the ®lm thickness was varied from 1800 to 500 A Ê . These changes are attributed to the quantum size effect in semiconducting ®lms. # 1999 Elsevier Science S.A. All rights reserved. Keywords: HgS ®lms; SEM; Blue shift; Chemical deposition 1. Introduction Chemical deposition is for preparing semiconductor layers and has been used mainly for metal sul®des and selenides. Due to the interest in HgS over the last decade, which has been generated largely by its potential use in solid state solar cells, photoelectrochemical cells. Photoconduc- tors etc., a simple chemical method of preparing chalco- genide has been investigated by many groups [1,2]. Recently, nanocrystalline ®lms of CdS, CdSe and PbSe have been prepared by both chemical and electrochemical methods. Photoelectrochemical cells based on nanocrystal- line CdSe and CdS have been studied. CdSe ®lms have been prepared from- nitrolotetra±acetic acid (NTA) -complexed bath of pH value of 10.7 [3±6]. A blue shill in band gap E g , of 0.2 eV and grain size between 40 and 80 A Ê were observed, depending upon preparative parameters. It has been reported that there is a certain critical ratio between the complexing agent and metal ion concentration which controls the grain size [7,8]. Recently Gadave et al. [9] reported the chemical deposi- tion of HgS thin ®lms from acidic bath at room temperature by optimizing preparative parameters. In the present study, HgS ®lms have been prepared and the effects of some of the preparative parameters on the properties of HgS thin ®lms are studied with the help of optical absorption XRD, elec- trical receptivity SEM and TEM techniques. 2. Experimental procedure 2.1. Sample preparation For deposition of HgS ®lms, 0.05 HgCl 2 solution was taken in a beaker, equal volume of 0.1 M Na 2 S 2 O 3 solution was added to it and clean microslides were introduced in the beaker. The deposition temperature was varied between 273 and 358 K and deposition time was varied between 45 min and 72 h. The thickness of the ®lms was measured by Fizzau Fringe method. The thickness of the ®lm was between 500 and 1800 A Ê . 2.2. Sample characterization In the present study, HgS ®lms have been studied by following techniques: Optical absorption XRD, SEM, TEM and electrical resistivity. In order to ®nd out the change in optical band gap of HgS, optical absorption of HgS ®lms was carried out in the wavelength range from 3500 to 8500 A Ê with the spectrophotometer Hitachi-300. Philips PW-1710 X-ray diffractometer using Cu Ka radiation with wavelength 1.542 A Ê was used to ®nd out the average grain size in HgS ®lms. The X-ray machine was operated on 25 kV, 20 mA. Materials Chemistry and Physics 59 (1999) 242±246 *Corresponding author. 0254-0584/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved. PII:S0254-0584(99)00048-6