Two-dimensional Electron Gas Structure Superlattice Thin Films And Their Laser Induced Thermoelectric Voltage Effect

SrTiO3, SrTi0.8Nb0.2O3 and LaAlO3 polycrystalline ceramic targets were prepared by solid-phase sintering and coprecipitation methods, respectively. Then, they were tested by XRD. Optimal deposition conditions of SrTi0.8Nb0.203/LaAlO3(001) single layer thin films, SrTiO3/SrTi0.8Nb0.2O3/LaA103(001) superlattices and LaAlO3/SrTi0.8Nb0.2O3/LaAlO3(001) superlattices thin films, first of all, were accomplished by the way of pulsed laser deposition (PLD) technique, thereafter, serials of SrTi03/SrTio.8Nbo.203/LaA103(001), LaA103/SrTi0.8Nb0.2O3/LaAlO3(001) superlattices with two-dimensional electron gas structure, as well as SrTi0.8Nb0.2O3/LaAlO3(001) single layer thin films were prepared on LaAlO3 (100) single crystalline substrates of tilted angle 0°and 15°. The results of XRD show that all films were c oriented. At the same time, the superlattices were characterized by X-ray diffraction in which regularly distributed satellite peak structure was observed, which illuminated that the superlattices samples were high quality. Using satellite peaks in the XRD patterns, the deposition rates of SrTiO3 and SrTio.8Nbo.2O3 were calculated, respectively, as 0.36nm/pulse and 0.26nm/pulse, and thicknesses of the thin films also were obtained.Laser induced voltage (LITV) signals were measured on the films grown on vicinal-cut substrates for the first time. This can be able to prove that these superlattices were a new type atomic layer pile materials. Comparing the LITV signals of all samples show that LITV signal peak value voltage is proportional to the incident laser energy. Superlattice did not behaved as one'sexpectation, instead, they always show lower LITV signals than SrTio.8Nb0.2O3/LaAlO3(001) single layer thin films. Moreover, the LITV signals became much lower when the SrTiO3 dielectric layers were replaced by LaAlO3. The experimental results were analysized and discussed, and possible mechanisms were posed as well.Lastly, the LITV signals of SrTi0.8Nb0.2O3/LaAlO3(001) single layer thin film (2#) and SrTi03/SrTio.8Nbo.203/LaA103(001) Superlattice (6#) were fitted by pulse function. According to the equation of fitting curve, the decay time constant of LITV signals were obtained. Using the relationship of the decay time constant, the thickness of films and the thermal diffusion constants, the thermal diffusion constants of the two samples were calculated for 5.65×10-7m2/S and 2×10-6m2/S. Then, under the appropriate approximate conditions, substituting the thermal diffusion constants, the thermal conductivity, the decay time constant and so on into time-dependence formula of LITV, anisotropic Seebeck coefficients were separately calculated for SrTi0.8Nb0.2O3/LaAlO3(001) single layer thin film(2#) (Sab-Sc)=14.4μVK-1 and SrTiO3/SrTi0.8Nb0.2O3/LaAlO3(001) superlattices (6#) (Sab-Sc)=1.9μVK-1。...