~ ) Pergamon Solid State Communications, Vol. 89, No. 4, pp. 349-352, 1994 Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038-1098/9456.00+.00 0038-1098(93)E0089-G " PREPARATION OF n-TYPE DOPED FeS THIN FILMS" 2 I.J. Ferrer, F. Caballero, C. De las Heras, C. Sanchez Dpto. de Fisica de Materiales, C-IV, U.A.M. Cantoblanco, 28049-MADRID (SPAIN) (Received 1 June 1993 by D. Van Dyck) N-type pyrite thin films have been prepared by sulfuration at 350°C of flash evaporated Fe-X (X =AI, Cu, Ni) layers. Physical and structural properties have been investigated. XRD showed pyrite structure. Room temperature dark resistivity of the films varies from O.21 to 7.10 -4 ~2.cm depending on the impurity concentration. Hall mobilities are between 1 and 104 cmZ/V's. Optical properties are also drastically affected by doping. 1. INTRODUCTION. Recently there is a great interest in growing FeS 2 single crystals 1-4 and thin films 4-12 for solar energy applications. However, up to now, highly efficient FeS films have not been obtained because z of the many parameters determining their photoactivity which are mainly related to the stoichiometry (i.e. sulfur and iron vacancy densities) and doping level (impurity type and concentration). Stoichiometry influence on FeS properties has been 2 previously investigated in natural 2J3-14 and synthetic crystals l'z'4'SJa-ls and in thin films. TM The role of some impurities appearing in synthetic samples during the formation processes Table I: Film impurity concentrations and stoichiometric ratios measured by EDAX and (*) TXRF. TXRF measurements were carried out in non sulfurated layers and EDAX in sulfurated ones. (X/re is the impurity to iron atomic ratio. S/Fe is the stoichiometric one. S/Me is the atomic ratio when considering all the metal content of the film, i.e. X + Fe). Values in parenthesis are calculated from EDAX measurements. Nominal impurity X/Fe (7*) S/Me S/Fe co ncent r a t ion --- 2.14 17. Cu 0.57* AI 2.07. A1 107. AI 0.5% Ni 2.07* Ni 107. Ni -=0.33" -=4. 16 -=28. 40 o -=0.25 -=4. 60 ----24 . O0 (2. 15) 2.08 0.94 (2. I O) 2.O1 2.00 2.16 2.00 2.17 1.66 2.10 2.19 2.48 349