Influence of thickness and illumination on electrical properties of MOS capacitor of spray-pyrolyzed mixed phase CdTe2O5-CdTeO3-CdTe film

Spray pyrolysis technique maintaining at substrate temperature of 350°C was used for synthesis of mixed phase cadmium telluride thin films of various thicknesses (55–95 nm) at variable deposition times of (15 s, 20 s, and 25 s), and MOS capacitor was fabricated on n-silicon (100) using air as the carrier gas. The structural, compositional, and morphological studies were carried out using XRD, Raman spectroscopy, photoluminescence, EDAX, and SEM, respectively. The XRD studies confirm the polycrystalline phase of both CdTeO3 and CdTe. The grain size estimated from XRD and SEM was found to be 170 nm and 33 nm, respectively. EDAX revealed no other elemental impurities in these films other than Cd (37.06 wt%) and Te (62.07 wt%). The tellurium-rich film was confirmed by Raman spectroscopy. PL peak obtained at 825 nm confirmed band-to-band recombination in CdTe. The electrical study was performed on the fabricated photovoltaic MOS structure, and various electrical parameters such as ideality factor (n), zero-bias barrier height (∅b0), saturation current density (Is), and series resistance (Rs) were obtained from the MOS I-V characteristics under both dark-light conditions which may work as light addressable potentiometric sensor. The flat band voltage (VFB), interface state concentration (Nis), oxide charge concentration (ND), and effective charge concentration (NEFF) were extracted from the frequency dependent C-V characteristics of the MOS capacitor. The electrical study reveals that both oxide thickness and applied frequency affect the electrical parameters of spray deposited mixed phase CdTeO3 MOS capacitor, due to potential drop at interfacial layer, large defect densities, and pinholes in the spray deposited insulating layer.