Light-induced Voltage Effect In BiCuSeO_based Thin Films Or Heterojuction

Light-inducedtransversethermoelectric?LITT?effectisanunconventional thermoelectric phenomenon in which heat and electric energy flow through a material perpendicular to each other,and it has been extensively studied in recent years due to the potential application in wide-band light detectors.In this paper,c-axis tilted BiCuSeO thin films as well as BiCuSeO/Si heterojunction were prepared by using pulsed laser deposition technology.The influences of illuminated laser wavelength,energy,measured temperature and the size of Au particles on the LITT effect in BiCuSeO thin film have been investigated.Furthermore,the temperature-dependent rectifying and photovoltaic characteristics of the BiCuSeO/Si heterojunction have also been explored.The main experimental conclusions are as follows:1.?a?When the film surface is irradiated by a light?heat?source,such as a 308nm pulsed laser,or a continuous laser with wavelength of 532 nm,808 nm,2200 nm,or even a point-like thermal heater,obvious open-circuit voltage signals have been observed,and the origination of the observed signals is suggested from the anisotropic Seebeck coefficient of the material.?b?The amplitude of induced voltages V_p increases with decreasing the wavelength of irradiated lasers or increasing irradiation power,which both can cause an increased the light temperature difference?35?T_z between top and bottom surface of the film generated by the laser illumination.?c?At temperature range of 300-80K,upon the irradiation of a 532nm continuous laser,V_p decreases with the decreased measured temperature,which can be attributed to the reduced anisotropy of the Seebeck coefficient as well as the increased thermal conductivity of BiCuSeO thin film at lower temperature.2.The effect of the nano-Au particles size on the LITT effect has been investigated,and we found that:?a?Au particles with diameter of 7-20nm can enhance the light absorption and light-to-heat conversion efficiency in LITT effect,and the larger size or the more dense of the nano-Au particles,the improvement degree is more obvious;?b?Upon the irradiation of a308nm pulse laser,nano-Au particles can optimize sensitivity as well as response time of the LITT voltage signals from BiCuSeO thin films.The optimal improvement in sensitivity is obtained when the average diameter of the Au particles layer is about 13nm;?c?The overly dense Au particles on the the film surface can become a conductive layer,which will result in a decreased V_p and a faster response time in the LITT voltages.3.Temperature-dependent rectifying and photovoltaic characteristics of the BiCuSeO/Si heterojunction have been investigated.?a?The I-V curve exhibits a significant rectifying behavior,and the carrier transport characteristics under forward bias can be explained by the trap-filled space charge-limited currents?SCLC?conductivity mechanism.At lower temperature?300-20K?,the I-V curve moves to rightward for positive bias and to downwards for reverse bias.?b?When a continuous laser with wavelength of 532nm,671nm,808nm or980nm is illuminated on Bi CuSeO film surface in the BiCuSeO/Si heterojunction,obvious open circuit voltage V_occ and short circuit current I_scc can all be detected.Moreover,V_occ increases with increased wavelength of the irradiated laser or irradiated laser power.Highest sensitivity in V_occ as well as I_scc is obtained for the irradiation of a 980nm light source.These phenomena can be well explained by the related theory of ideal heterojunctions.?c?As measured temperature decreases from 300K to 20K,a thicker space charge layer and an enhanced barrier lead to an increased V_oc.The research works indicate that BiCuSeO-based compounds have potential application not only in high temperature thermoelectric field but also in wide-band light detectors or optoelectronic device design,and other fields.