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

Results of photoconductivity rise and decay, optical absorption and photoco nductivity excitation spectra are presented for different chemically deposi ted (Cd-Pb)S films. The ratio of saturated photocurrent of rise curves (I-p c) to dark current (I-DC) is found to be of the order of 10(5) for undoped (Cd-0.95-Pb-0.05)S films which improves to 10(6) for the systems prepared w ith NaF end Lanthanum/Neodymium nitrate. When annealing the films at 400 de greesC for 2 minutes, the dark current decreases to almost zero, along with a decrease in the photocurrent, but the I-pc/I-DC ratio goes to a very hig h value. From the analysis of the decay curves lifetime of carriers are fou nd to be 31.11 sec, 48.01 sec, 47.77 sec and 94.66 sec for (Cd-0.95 - Pb-0. 05)S; (Cd-0.95 - Pb-0.05)S: NaF; (Cd-0.95 - Pb-0.05) S: NaF, La and (Cd-0.9 5 - Pb-0.05)S: NaF, Nd respectively. Further the mobility of carriers for t hese systems are found to be 51.44cm(2)/V-s, 93.33 cm(2)/V-s, 94.83 cm(2)/V -s and 164.78 cm(2)/V-s respectively. Band gaps determined from optical abs orption and photoconductivity excitation spectra gave similar results. The direct band gap nature is found for mixed films. Results of different irrad iation conditions during preparation of the films; are also investigated.