The influence of substrate temperature on electrical properties of Cu/CdS/SnO2 Schottky diode

Polycrystalline CdS samples on the SnO₂ coated glass substrate were obtained by vacuum evaporation method at low substrate temperatures (T_S=200 and 300 K) instead of the commonly used vacuum evaporation at high substrate temperatures (T_S>300 K). X-ray diffraction studies showed that the textures of the films are hexagonal with a strong (0 0 2) preferred direction. Circular Cu contacts were deposited on the upper surface of the CdS thin films at 200 K by vacuum evaporation. The effects of low substrate temperature on the current-voltage (I-V) characteristics of the Cu/CdS/SnO₂ structure were investigated in the temperature range 100-300 K. The Cu/CdS (at 300 K)/SnO₂ structure shows exponential current-voltage variations. However, I-V characteristics of the Cu/CdS (at 200 K)/SnO₂ structure deviate from exponential behavior due to high series resistance. The diodes show non-ideal I-V behavior with an ideality factor greater than unity. The results indicate that the current transport mechanism in the Cu/CdS (at 300 K)/SnO₂ structure in the whole temperature range is performed by tunneling with E₀₀=143 meV. However, the current transport mechanism in the Cu/CdS (at 200 K)/SnO₂ structure is tunneling in the range 200-300 K with E₀₀=82 meV.