INSTITUTE OF PHYSICS PUBLISHING SEMICONDUCTOR SCIENCE AND TECHNOLOGY Semicond. Sci. Technol. 21 (2006) 76–80 doi:10.1088/0268-1242/21/1/014 Passivation properties of CdS thin films grown by chemical bath deposition on GaSb: the influence of the S/Cd ratio in the solution and of the CdS layer thickness on the surface recombination velocity O Vigil-Gal´ an 1 , J N Ximello-Quiebras 1 , J Aguilar-Hern´ andez 1 , Gerardo Contreras-Puente 1 , A Cruz-Orea 2 , J G Mendoza- ´ Alvarez 2 , J A Cardona-Bedoya 3 , C M Ruiz 4 and V Berm ´ udez 4 1 Escuela Superior de F´ ısica y Matem´ aticas-IPN, CP 07738, M´ exico DF, Mexico 2 Departamento de F´ ısica, CINVESTAV-IPN, AP.14-740, CP 07360, M´ exico DF, Mexico 3 Departamento de F´ ısica, Universidad del Tolima, Ibagu´ e, Tolima, Colombia 4 Departamento de F´ ısica de Materiales, Facultad de Ciencias, Universidad Aut´ onoma de Madrid, 28049, Madrid, Spain E-mail: orea@fis.cinvestav.mx Received 9 August 2005, in final form 25 October 2005 Published 9 December 2005 Online at stacks.iop.org/SST/21/76 Abstract Evidences of the passivation effect are given when thin films of CdS are deposited on GaSb crystalline substrates, using a bath chemical deposition method. The passivation process is studied through photoacoustic and photoluminescence experiments. The surface recombination velocity calculated from photoacoustic measurements decreases and the radiative recombination rate as measured from photoluminescence spectra increases when the nominal S/Cd ratio in the layer deposition solution increases. The influence of the CdS layer thickness on the surface passivation of GaSb is also studied. 1. Introduction GaSb and their ternary semiconductor compounds are important materials for optoelectronic applications, especially in thermophotovoltaic (TPV) systems. One problem concerning the use of GaSb in the TPV technology is the cost of these cells. The cost of the photovoltaic cells is related to the substrate itself and the processing on the device. One possibility of reducing the wafer cost is the use of polycrystalline material; while for the reduction of the processing cost, the substitution of the based diffusion technology for the surface deposition of n-type material on p-type polycrystalline substrate one could be an alternative solution. Furthermore, problems related to the high surface defect densities and residual native oxide layers limit these applications, since TPV devices with high surface recombination velocity (SRV) degrade the quantum efficiency and the electrical properties of the cells, and therefore the final energy conversion efficiency. The measured or calculated SRV value varies depending on the type of substrate studied (values in the order of magnitude between 10 2 and 10 6 cm s −1 have been reported). Usually intrinsic p-type samples have a high SRV. In p-type Zn-doped samples, the SRV can be reduced by the Zn-doping profile or by the use of a GaInSb window [1–3]. The profile of the built-in electric fields (fields which are due to the doping gradient and to the band gap gradient caused by the effect of band gap narrowing) 0268-1242/06/010076+05$30.00 © 2006 IOP Publishing Ltd Printed in the UK 76