Perovskite-type Oxide Thin-film Laser Induced Thermoelectric Voltage Effect And Photodetector Applications

Based on the anisotropic structure and charge transport properties, the laser induced thermoelectric voltage (LITV) effect and the application in photo detection are studied in three types of perovskite-related layered oxides, including YBa2Cu3O7-x (YBCO), La2-xSrxCuO4 (LSCO) and Nd2-xCexCuO4 (NCCO) thin films.For the first time, the transverse laser induced voltages are detected in the tilted LSCO and NCCO thin films. According to the dependence of the detected signals on the lasers energy, wavelength and the charge carrier concentration of the films, the measured voltages are confirmed to be the LITV signals. LSCO and NCCO thin films are proved to be new types of applicable atomic layered thermopile materials (ALTMs). While the LITV signals detected in YBCO thin films are found to be enhanced by 2～4 times with the increasing of annealing oxygen pressure by which the films with large oxygen content can be prepared. When illuminated by 0.78mJ ultraviolet laser pulse (the pulse duration is 28ns), the YBCO films which annealed at 105Pa oxygen pressure get a sensitive LITV signal of 21.6V which is the largest LITV response up to now. In YBCO films, the measured LITV signals depend on the oxygen content so drastically, which suggests that charge carrier concentration is very important to the LITV effect.The models for the description of LITV effect are posed based on the interaction of the laser pulses and the thin films, and the clear expressions of the peak values and response time have been deduced.In order to serve for the design and fabrication of LITV type laser energy/power meters, an equation on the figure of merit for detectors is also obtained. It is demonstrated that LITV signals are mainly dominated by the anisotropic Seebeck coefficient and the lasers penetration depth, while the response time is just determined by the thermal transition properties of the films.The influence of ionic dopant on LITV effect reveals the anisotropic thermoelectric transport behaviors in the perovskite-related oxide. As to YBCO thin films, the dependence of LITV signals on the annealing oxygen pressure is found to be in accordance with that of the thermoelectric anisotropy on the oxygen content. The analogical result is also observed in the vicinal LSCO thin films. The common behavior of LITV signals is explained to be associated with a two-dimensional characteristic of the localized carriers in these oxides. In LSCO thin films, the detected LITV signals are increasing firstly as the Sr-dopant increases, and up to the maximum at x=0.15. Further increasing of doping level makes the voltage decrease to zero however. It is just in the films with 0.05