Effect of doping on trapping center parameters in nanocrystalline CdSe thin films

Thin films of the undoped nanocrystalline CdSe (nc-CdSe) and doped (Zn and In) thin films have been prepared by physical vapor deposition in the presence of argon as inert gas at room temperature. The influence of the doping materials on the stoichiometry, grain size and trap parameters has been explored by means of Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM) and thermally stimulated current (TSC) measurements. The TEM results show that small particles of nanometer range are formed in thin films and that size increases slightly with Zn doping and decreases when In is used as the doping material. TSC measurements in the temperature range from 225 to 350 K are performed at different heating rates. Well defined TSC peaks have been observed. The peaks shift to higher temperatures as heating rate is increased. Trap parameters, such as trap depth and density of traps have been determined. The trap parameters have been evaluated by using Gaussian fit and different heating rates methods. Good agreement has been obtained between trap parameters calculated from these two methods. It is observed that the trap depth decreases and trap density increases in doped samples compared to undoped ones.