The effects of ,, - irradiation on the optical and electrical properties of buffer solution

Abstract

Pure and aluminum doped (0.001 wt %Al) CdS thin films were deposited on microscope glass slides using buffer solution growth technique based on CdSO4 as the cadmium source, thiourea as the sulphur source, and (NH4)2 SO4 as a buffer. The effects of gamma radiation on the optical and electrical properties of the CdS films have been investigated by measuring their optical absorbance and electrical conductivities before and after irradiation by different doses of  – radiation in the range 7.27 × 102 to 2.04 × 105 Gy.



The absorbance was found to be dependent on film's thickness (and aluminum dopant concentration) and  – radiation doses. CdS films (pure and doped)  – irradiated at high doses (2.6 × 106 Gy) have the lowest absorbance. Gamma – irradiation induced dark electrical conductivity in CdS films, which was dependent on absorbed  – radiation dose rate. The conductivity was permanent at high  – radiation dose (2.04 × 105 Gy) and transitory below this dose.



Generally, the optical band gap values if unirradiated and  – irradiated CdS : Al films were lower than that of pure CdS films. The band gaps and electrical conductivities of pure and CdS : Al films, unirradiated and irradiated at low  – radiation doses (≤ 1.45 × 104 Gy) are the same i. e., 2.43 ± 0.02 eV and 0.068 ± 0.005 (-cm)-1, and 2.31 ± 0.02 eV and 0.69 ± 0.05 (-cm)-1 for pure and CdS : Al films respectively. At high  – radiation doses, the band gaps decreased to 2.30 eV and below 2.30 eV for pure and CdS : Al films respectively, accompanied by increase in the dark electrical conductivties.



Possible mechanisms responsible for the observed changes are briefly discussed.

Global Journal of Pure and Applied Sciences Volume , No 1 January (2001) pp. 147-152



KEY WORDS:

Cadmium sulphide films, gamma – irradiation, Solar cells properties.