INVESTIGATION OF LITHIUM - NIOBIUM TRIOXIDE THIN FILMS IN MIS STRUCTURE (FERROELECTRIC)
Doctor of Philosophy
Thin film LiNbO(,3) was deposited on silicon substrates by using r.f. sputtering techniques under different conditions. A set of films was deposited with different substrate temperatures and with different gas mixtures between O(,2) and Ar to study the effect on crystallinity and electrical properties. X-ray diffraction was used to study the crystal structures of the films. It was found that good polycrystalline films were obtained when O(,2) and Ar were used at the equal partial pressures and the substrate temperature was raised to above about 550(DEGREES)C. At the substrate temperature much below 550(DEGREES)C the film is amorphous. The bulk photovoltaic effect was studied in these films. I-V characteristics under dark and illuminated conditions indicated that there was a photovoltaic effect in these films. The saturation field was estimated to be about 4.1 KV/cm and the short-circuit photocurrent was 9 pA at the light intensity 29 mW/cm('2). The low saturation field was attributed to the high photoconductivity of the thin film. The transient photocurrent was also studied and it was attributed to the pyroelectric effect. C-V and G-V characteristics under dark and post-illuminated conditions confirmed that the photovoltaic effect was indeed the bulk photovoltaic effect. C-f and G-f characteristics had different features at low frequency for polycrystalline and amorphous films. For the amorphous film (sample 17c), the capacitance varied as 1/SQRT.((omega)) and the conductance varied as SQRT.((omega)). For the polycrystal- line film sample 16c, the capacitance almost did not change with frequency. The conductance varied with the frequency faster than that of the amorphous film, and close to the frequency dependence of the conductance calculated from the second circuit model given in fig. 5.9 b).
Electronics; Electrical engineering