The influence of deposition conditions and alloying on the electronic properties of amorphous selenium

Electronic properties of a-Se as a function of the source (boat) temperature and as a function of As (up to 0.7%) and Cl (up to 40 wt ppm) concentrations have been experimentally studied by carrying out conventional and interrupted field time-of-flight (IFTOF) transient photoconductivity measurements that provide accurate determinations of the drift mobility and the deep trapping time (lifetime). No variation in electron and hole lifetimes and mobilities for pure a-Se was observed with the source temperature, that is, no dependence was observed either on the deposition rate or on the vapor composition. The addition of As reduces the hole lifetime but does not change the hole mobility. At the same time, As addition increases the electron lifetime while reducing the electron mobility. The electron range mutau, however, increases with the As content, which means that the overall concentration of deep electron traps must be substantially reduced by the addition of As. Cl addition in the ppm range increases the hole lifetime but reduces the electron lifetime. The drift mobility of both carriers remains the same. We interpret the results in terms of a shallow-trap-controlled charge transport in which deep traps are due to potential under- and overcoordinated charged defects that can exist in the structure. (C) 2003 MAIK "Nauka/Interperiodica".