Effects of oxygen and chlorine on charge transport in vacuum deposited pure a-Se films

We have investigated the effects of oxygen and chlorine addition in the ppm range to pure amorphous selenium (a-Se) in terms of electron and hole transport in vacuum-deposited films. We examined the electron range (μeτe) and hole range (μhτh) by carrying out time-of-flight (TOF) and interrupted field time-of-flight (IFTOF) transient photoconductivity measurements. We have found that even small amounts of oxygen in the ppm range can significantly affect both electron and hole lifetimes. Oxygen addition increases the hole lifetime and decreases the electron lifetime. As the oxygen doped a-Se films age, the hole lifetime has a tendency to decrease while the electron lifetime shows a slight improvement. In contrast, chlorine addition almost totally annihilates electron transport while the hole transport remains relatively unaffected.