For the first time, SiO2 layers, prepared by direct photochemical-vapor deposition, were passivated onto HgCdTe substrates using a deuterium (D-2) lamp as the ultraviolet and vacuum-ultraviolet light source. It was found that the refractive index of the SiO2 films, grown at 60 degrees C and 0.5 Torr for a mixture of SiH4 and O-2, is close to 1.462 (the refractive index of thermal silicon dioxide) when the gas ratio (SiH4/O-2) is adjusted to 0.2. Various characterization techniques, such as x-ray photoemission, Auger-electron, and Fourier-transform spectroscopies were used to give a detailed study of the physical and chemical properties of the SiO2 thin films. The electrical properties of these SiO2 layers were investigated by performing high frequency (1 MHz) capacitance-voltage (C-V) and current-voltage (I-V) measurements, at 77 K. The C-V measurement shows that the minimum interface state density is 5x10(10) cm(-2) eV(-1) with a hysteresis smaller than 0.2 V. The maximum dielectric strength observed from I-V measurement is around 580 kV/cm.