Growth phases during electrochemical selenization of vacuum deposited CuInmetal layers for the formation of semiconducting CuInSe2 films

A new two-stage process for electrochemical selenization of vacuum deposite d Cu-In precursor films is demonstrated as an alternative to toxic and haza rdous H2Se or Se vapour phase selenization techniques for the formation of semiconducting CuInSe2 thin films. The growth phases and microstructure of films are sensitive to Cu to In thickness ratios in the precursor, seleniza tion current densities and time. Electrochemically selenized films show mul tiphase and polymorphic behaviour which strongly depends on the precursor s tructure and composition. The crystalline state of the film varies from a s phalerite to chalcopyrite CuInSe2 phase along with Cu and In binary compoun ds which are also observed. With In in excess in Cu + In mixed precursor fi lms, use of low selenization currents (1 mA/cm(2)) and longer periods (3 h) yield the chalcopyrite CuInSe2 phase. Copper excess in bilayer precursor l ikewise favours chalcopyrite CuInSe2 growth after a post-selenization annea ling. Single-phase chalcopyrite CIS film formation requires full selenizati on of the precursor and proper adjustment of the Cu/In thin film ratio in t he precursor. Absence of free selenium at the post-selenization annealing s tage led to secondary reactions and inclusion of binary phases. (C) 1999 Pu blished by Elsevier Science S.A. All rights reserved.