Optical, electrical and structural properties of indium-doped cadmium oxide films obtained by the sol–gel technique

Indium-doped cadmium oxide films were obtained by mixing cadmium oxide and indium oxide precursor solutions by the sol–gel technique. The indium atomic concentrations in solution (x) studied were 0, 2, 5 and 10 at%. The films were sintered at two different sintering temperatures (Ts) 350 and 450 °C, and after that annealed in a 96:4 N2/H2 gas mixture atmosphere at 350 °C. X-ray diffraction patterns showed that all films sintered at Ts=350 °C only consisted of cadmium oxide crystals. The films sintered at Ts=450 °C consisted of cadmium oxide crystals also; however, for the highest indium atomic concentration (10 at%) the formation of cadmium indate oxide crystals was evident. All films show high optical transmission (>85%) and an increase of the direct band gap value from 2.4 to 3.1 eV, as the indium atomic concentration in solution increases. The minimum resistivity value obtained was 6.3×10−4 Ω cm for the films with x=5 at%, Ts=450 °C and annealed at 350 °C.