Influence of trapping and de-trapping charge in MOS-like structures with single and twofold SiOx films as active layers

Single and twofold non-stoichiometric silicon oxide (SiOx) films are considered as an active layer in metal oxide semiconductor (MOS)-like structures. Such films were obtained by hot filament chemical vapor deposition (HFCVD) technique in the range of temperatures from 900 °C to 1150 °C. They were subjected to a thermal annealing at 1100 °C. In order to know their optical and electrical properties, their transmittance spectra, absorption coefficients, absorbance (FTIR) spectra, photoluminescence (PL) spectra, current-voltage (I-V) curves and capacitance-voltage (C-V) ones were obtained. The optical energy gap of twofold SiOx films as a function of the growth temperature (Tg), suffers non-linear variations in the range from 2.25 to 1.8 eV when we make combinations of different Tǵs in both films; besides, such films exhibit compositional changes when Tg is varied and a restructuration (phase separation) takes place because of thermal annealing. Light emission in single and twofold SiOx films is ascribed to both silicon nanocrystals (Si-ncs) and some kinds of defects, which are produced during the growth process and thermal annealing. In the case of twofold films it is observed that the effect of thermal annealing induces emission in the orange-near infrared range and in the violet-blue bands but without the presence of the green-yellow band. MOS-like structures using single and twofold films, show different electrical phenomena such as the influence of trapping and de-trapping charge. The influence of Si-ncs and defects gives place to spike and stair-like behaviour in I-V curves. Measurements of the electrical I-V and C-V curves are obtained under dark conditions.