Electrical studies on trap levels present in n- and p-type spray pyrolysed CdS thin films

Abstract

Trap levels in n- and p-type spray pyrolysed CdS thin films were analysed using thermally stimulated current (TSC) and dark-conductivity measurements. TSC measurements of the n-type sample revealed the presence of only one peak under light excitation for a short period due to mobility of sulphur vacancies, but longer excitation could give evidence of one more level which was due to a complex of cadmium and sulphur vacancies. TSC spectra of the p-type sample indicated the presence of two levels of comparable cross section irrespective of light excitation time, which correspond to mobility of the sulphur vacancy and copper impurity. TSC measurements on air annealed n-type samples indicated the presence of a level due to the sulphur vacancies and another level may be due to chemisorbed oxygen. However vacuum annealed samples showed results similar to those of as-prepared n-type samples. The dark-conductivity measurements of these samples were found to be in good agreement with the TSC measurement results.

Trap Levels in RF Sputtered CdS Thin Films

“…The level is observed in sample CS5 Zhao et al [8] detected the level at 0.47 eV using photoluminescence measurements and attributed it to a native defect (cadmium interstitial?). Also Zeenath et al [4] and Vigil et al [6] reported on a level at 0.41 eV detected using TSC measurements and attributed it to a complex native defect (cadmium and sulfur vacancies complexes?) 6.…”

“…L9 (0.72 eV): The level is observed in sample CS5. Zeenath et al [4] observed a level at 0.75 eV using TSC measurements which they attributed to copper impurities.…”

“…Deep levels in CdS have been previously studied using a number of characterization techniques including DLTS [1][2][3], thermally stimulated current (TSC) [4], photoconductivity [5][6][7], photoluminescence [1,8] and PICTS [9,10]. Energy levels in the range 0.033-1.3 eV have been reported.…”