碲化铋薄膜载能粒子相互作用的超快研究

碲化铋禁带宽度非常窄而具有高电导率和塞贝克系数,同时具有低热导率,成为已知室温下优值系数最高的热电材料。已有研究表明,纳米薄膜和超晶格是进一步提高材料热电性能的可行途径。因此超快研究碲化铋纳米薄膜中载能子间的相互作用过程对开发高性能热电材料有重要意义。本文采用飞秒激光泵浦-探测技术,实验研究了沉积在硅基底上厚度为100 nm碲化铋薄膜中各载能粒子的相互作用过程。通过改变延迟时间步长,分别观察到价带电子被光子激发跃迁至导带,激发电子在导带内与声子的能量弛豫及导带电子与空穴复合跃迁至价带,并将能量传递给声子导致声子温度升高的过程。此外,还观察到热应力产生的声波,并据此得到了碲化铋薄膜中纵波声速为2649 m s^-1。

Ultrafast Study of Carrier Interaction in Bismuth Telluride Thin Film

Bismuth telluride,with narrow band gap,large electrical conductivity,large Seebeck coefficient,and low thermal conductivity,is one of the best thermoelectric materials with the highest figure of merit at room temperature.In addition,thin film and supcrlattice are considered to be the feasible ways to improve the performance of thermoelectric materials.And hence,it is important to study the carrier interaction in bismuth telluride thin film.In this paper,the carrier interaction of 100 nm thick bismuth telluride film deposited on silicon substrate has been studied by applying the femtosecond laser pump-probe transient thermoreflectance technique.Different carrier interaction processes,including electrons excited from valence band to conduction band,electron-hole recombination, and energy coupling from photoexcited carriers to lattice have been studied respectively by changing the delay time step of the probe pulse.Also,an acoustic wave generated from the thermal stress has been observed and the corresponding extracted longitudinal wave velocity is 2649 m s^-1.