Photoconductivity of chemically deposited lanthanum/neodymium doped (Cd - Pb)S films

Abstract

Results of photoconductivity rise and decay, optical absorption and photoconductivity excitation spectra are presented for different chemically deposited (Cd–-Pb)S films. The ratio of saturated photocurrent of rise curves (Ipc) to dark current (IDC) is found to be of the order of 105 for undoped (Cd0.95–-Pb0.05)S films which improves to 106 for the systems prepared with NaF end Lanthanum/Neodymium nitrate. When annealing the films at 400°C for 2 minutes, the dark current decreases to almost zero, along with a decrease in the photocurrent, but the Ipc/IDC ratio goes to a very high value. From the analysis of the decay curves lifetime of carriers are found to be 31.11 sec, 48.01 sec, 47.77 sec and 94.66 sec for (Cd0.95–-Pb0.05)S; (Cd0.95–-Pb0.05)S: NaF; (Cd0.95–-Pb0.05) S: NaF, La and (Cd0.95 –- Pb0.05)S: NaF, Nd respectively. Further the mobility of carriers for these systems are found to be 51.44 cm2/V-s, 93.33 cm2/V-s, 94.83 cm2/V-s and 164.78 cm2/V-s respectively. Band gaps determined from optical absorption and photoconductivity excitation spectra gave similar results. The direct band gap nature is found for mixed films. Results of different irradiation conditions during preparation of the films are also investigated.