Electrochemically deposited bismuth telluride thin films Santosh Golia * , M. Arora, R.K. Sharma, A.C. Rastogi Materials Division, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi, India Abstract Thin films of bismuth telluride grown by electrochemical deposition technique on conducting glass and Mo sheet substrates, were characterized for their structural, morphological, optical and compositional analysis. These studies revealed polycrystalline an- isotropic and layered structure of these films with different compositional stoichiometry. In the present work electrochemical de- position of bismuth telluride thin films is studied as a dopant material in II–VI group absorber materials for photovoltaic application since it has a narrow optical energy band gap of 0.13 eV. In this deposition process different film growth parameters were optimized to get good quality of compositionally uniform bismuth telluride thin film. XRD analysis revealed a hexagonal symmetry with large c-axis lattice constants (Bi 2 Te 3 , Bi 2þX Te 3X ). Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 73.40.L; 73.60.F; 72.80.E; 82.45; 86.30.J Keywords: Bi 2 Te 3 ; Electrodeposition; Thin film 1. Introduction Thin films of bismuth telluride belongs to the class of V 2 VI 3 binary chalcogenide compound semiconductor with a very high figure of merit and anisotropy. These properties are used for their wide range utilization in various thermoelectric, optoelectronic and electrochemi- cal devices for example in solid-state refrigeration, heat pumps infrared sensors and high efficiency photovoltaic solar cells [1–6]. These films can work from room tem- perature to 130 °C and can efficiently be used for low value large-scale power generation and their polarity can be changed from p-type to n-type by increasing bismuth concentration in the film. Films of cadmium telluride doped with bismuth telluride can act as an absorber layer in the photovoltaic solar cell for maximum con- centration of solar radiation to obtain high temperature gradients across it to improve solar cell conversion of power out put. Extensive studies on Bi 2 Te 3 doping has been carried out by many researchers [6–11] for the optical, thermoelectric and electrical properties of bis- muth telluride thin films grown by vacuum deposition technique, sol–gel, spray pyrolysis, screen printing etc. The aim of these studies is to deposit high quality bis- muth telluride films by simple economic and efficient cathodic electrodeposition techniques [12–16] so that they can easily be used as a low band gap dopant in the materials for large-scale photovoltaic applications. For this we aim to electrodeposit and characterize by Bi 2 Te 3 films separately. These electrodeposited Bi 2 Te 3 thin films were characterized high-resolution spectroscopic techniques such as X-ray diffraction (XRD), SEM, energy dispersive X-ray spectrophotometer (EDX) and optical absorption spectroscopy to confirm the forma- tion of bismuth telluride by revealing their structural, morphological compositional and optical properties. 2. Experimental Thin films of bismuth telluride were cathodically de- posited on SnO 2 :F coated glass substrate having a re- sistance of 10 X/cm. The electrolytic solution contained 0.05 gm Bi(NO 3 ) 3 and 0.05 gm TeO 2 . pH of the solution was kept 2. Three-electrode electrochemical cell ge- ometry was used for the deposition with Pt as anode, saturated (SEC) calomel as reference electrode and the SnO 2 if coated glass was used as cathodic substrate. Deposition was carried out at 70 °C for 30 min. Powder X-ray diffraction was carried out on as deposited films using CuK a radiation in 2h range of 15–75° by powder X-ray diffractometer (D8 Advanced Brukder axs) at 35 kV, 30 mA. d values were calculated using relation * Corresponding author. 1567-1739/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S1567-1739(02)00200-6 Current Applied Physics 3 (2003) 195–197 www.elsevier.com/locate/cap