Comparative Study of Cadmium Sulfide Thin Films at Room and Low Temperatures Fabricated by Closed Space Sublimation Technique

Cadmium sulfide (CdS) thin films were prepared under vacuum onto glass slides by closed space sublimation technique. X-ray diffraction was used to identify and confirm the orientation and hexagonal wurtzite crystalline structure of CdS thin films. Optical analysis from UV-VIS-NIR ranges was used to calculate the thickness of the films by taking transmission spectrum using spectrophotometer. After annealing, these thin film samples were electrically characterized using Hall measurements at room and liquid nitrogen temperature (77K), by applying currents of 1 nA, 10 nA and 50 nA. Resistivity, mobility and carrier concentrations were calculated and effects of temperature, current and film thickness were studied. Resistivity in the range of 10 – 10 (Ohm.cm) (room temperature) and 10 – 10 (Ohm.cm) (liquid nitrogen temperature) has been demonstrated. Similarly, high carrier concentration values in the range of 10 - 10 (cm-3) have been demonstrated. With the increase in thickness and current, CdS thin film samples demonstrated a decrease in resistivity and a consequent increase in mobility. Correspondingly, a decrease in resistivity was found at room temperature (compared to low temperature), implying that CdS acts as insulator at low temperature. Overall a semiconductor behavior was exhibited and results confirmed these CdS thin film samples to be exceptional for use as window layer in CdTe/CdS hetero-junction solar cells fabrication.