Effects of the applied power on the properties of RF-sputtered CdTe films

In this work, the application of RF power in stepped mode during the growth process of CdTe films deposited on glass substrates at room temperature and their structural, morphological, and optical properties were studied. The working pressure and deposition time during deposition were 10 mTorr and 120 min, respectively, meanwhile the RF power was gradually varied from 30 W to 40 W. For comparison and reference, CdTe films with 30 W and 40 W (fixed power values) were also deposited, which resulted amorphous. The x-ray diffraction results of the films prepared with stepped RF power were polycrystalline with cubic structure and (111) as preferential orientation. The crystallite size of films changes from 16.6 to 29.2 nm as the rate of the stepped RF power increases. Raman spectra show that intensity of peaks located at 123, 140 and 164 cm(-1) increase with the increased rate of stepped RF power, as well as the rms-roughness and grain size values increase from 0.8 nm to 1.6 nm and from 62.8 nm to 92.1 nm, respectively. The UV-vis spectra show that the bandgap energy of the deposited CdTe films changes from 1.47 to 1.54 eV with the increased rate of stepped RF power. The obtained bandgap energy values of the CdTe films are adequate to be used as absorber material for photovoltaic applications into the ZnO/CdTe and CdS/CdTe solar cells.