The Light Induced Transverse Thermoelectric Effect In Bi CuSeO Thin Films

Light induced transverse thermoelectric effect?short for LITT effect? is an unconventional thermoelectric phenomenon, which originates from the anisotropy of Seebeck coefficient and can be detected only in c-axis tilted thin films or layered structures. This effect is very promising in the fields of high sensitivity and fast response optical detectors. BiCuSeO is a new chalcogenide thermoelectric material. Recently, the research interest of BiCuSeO is mainly focused on the conventional thermoelectric effect and there are few studies on the LITT effect. In this paper, we prepared c-axis tilted BiCuSeO thin films by pulsed laser deposition?PLD?, and investigated the effects of irradiation wavelength, incident direction, Pb doping and testing atmosphere on their LITT effect. The main conclusions are as follows:1. When irradiating the surface of BiCuSeO thin films by pulsed laser, CW laser or electric iron, open circuit voltage signals can be observed parallel to the surface, and we found that: a) the voltage decreased with increasing irradiation wavelength; b) the voltage increased linearly with the incident laser energy; c) if the film thickness is larger than the optical penetration depth, voltage polarity reversed when the laser incident from the substrate side. This voltage signals originate from thermal effect caused by ?Tz, which is also called light induced transverse thermoelectric effect.2. The effect of Pb doping on LITT effect of Bi_1-xPb_xCuSeO?0?x?0.12?thin films was also studied. It was found that when the film surface was irradiated with UV pulse laser?308 nm?, the amplitude Vp of the induced voltages first increased then decreased with increasing Pb concentration. The maximum value of Vp is obtained at the sample of x=0.08. On the one hand, the conductivity of the film increases with Pb content, leading to larger ?Tz; On the other hand, Pb doping deteriorates the orientation of grains, resulting in a decreased ?S. These two contradictory trends lead to the results observed in our experiments.3. The effects of measurement atmosphere and temperature on the LITT effect have been studied in Bi_0.92Pb_0.08 CuSeO thin films. When the film surface was irradiated by a CW laser?532nm?, the LITT voltage magnitude decreased with measured temperature due to the decreased ?S; and comparing to measure in air, the value of Vp is enhanced, which can be ascribed to the improved ?Tz caused by slow thermal relaxation.