掺杂Bi的β-Cu_(2)Se薄膜的微观结构与热电性能

Microstructure and Thermoelectric Properties of Bi-doped β-Cu_(2Se) Film

目的 探究在β-Cu_(2)Se薄膜中掺杂元素Bi对其组织结构及其热电性能的影响,探求Bi元素对载流子传输过程和热电性能的影响规律,为将来该类热电薄膜的研究和应用提供宝贵的经验。方法 使用粉末烧结制得Cu-Bi-Se合金靶材,使用磁控溅射的方法在含有SiO_(2)层的单晶Si衬底上制备了不同Bi含量的β-Cu_(2-x)Bi_(x)Se热电薄膜。利用X射线衍射仪、扫描电子显微镜、能谱仪分别研究了沉积薄膜的XRD谱、表面与截面形貌以及元素含量与分布。利用LSR-3电阻率/塞贝克系统测量了沉积薄膜的Seebeck系数与电导率。利用霍尔试验测量了沉积薄膜的室温载流子浓度和迁移率。结果 沉积薄膜主要由单一的β-Cu_(2)Se相构成,在Bi掺杂量最大为1.07%(原子数分数)的薄膜还含有非常少量的α-Cu_(2)Se相;在β-Cu_(2)Se相薄膜中Bi的掺杂没有生成单质相而是替换点阵中的Cu而形成替位式固溶体。在沉积的β-Cu_(2-x)Bi_(x)Se薄膜中,([Bi]+[Cu])/[Se]>2.0且具有p型导电特征。随着温度的增加,电导率降低而Seebeck系数增加,彰显沉积薄膜的简并或半简并半导体的导电特性。当温度低于225℃时,沉积薄膜功率因子随Bi掺杂量的增加而增大;当温度高于225℃时,掺杂量为0.29%(原子数分数)的薄膜具有最大的功率因子,进一步增加Bi掺杂量,沉积薄膜的功率因子却逐渐减小。结论 使用磁控溅射的方法可制备β-Cu_(2)Se薄膜,掺杂适量的Bi可显著提高薄膜的功率因子。

The Cu_(2Se) material Ms attracted more attentions in the field of thermoelectric materials due to its high figure of merit,"electronic crystal phonon liquid" structure,rich constituent elements in the crust,low price and other advantages.Compared with bulk material,the film with a nearly two-dimensional structure can effectively improve the Seebeck coefficient and reduce the thermal conductivity,showing excellent thermoelectric properties.At present,the main methods to improve the thermoelectric properties include element doping,composites containing nano-sized second phase,low dimensionalization,nano structure,etc.Element doping can modulate the carrier concentration and change the energy band structure,further modulating the Seebeck coefficient and electrical conductivity.Therefore,element doping has been proved to be one of the most effective methods to improve the thermoelectric properties of materials.Bi has a larger atomic radius compared with Cu.This means that doping Bi may cause lattice distortion and more point defects in Cu_(2Se) lattice.At the same time,phonons are scattered in transmission due to mass fluctuation and periodic stress field destruction due to Bi doping,thus reducing the thermal conductivity.Thus,Bi doping helps to improve the thermoelectric performance of materials.In this work,The β-Cu_(2-x)Bi_(xSe) thermoelectric films with different Bi contents were prepared by magnetron sputtering on single crystal Si substrate containing SiO_(2) layer with high vacuum powder sintered Cu-Bi-Se alloy target.The phase composition of deposited films was determined by XRD patterns and the surface and cross-sectional morphology of deposited films was observed by SEM.The content and distribution of the constituent elements were measured and analyzed by EDS.The Seebeck coefficient and electrical conductivity of deposited films were measured by LSR-3 resistivity and Seebeck system.The carrier concentration and mobility of deposited films at room temperature were measured by Hall experiments.The results showed that deposited films were mainly composed of single β-Cu_(2Se) phase at room temperature.The films with the maximum Bi doping amount of 1.07at.% also contained very small amount of α-Cu_(2Se) phase and β-Cu_(2Se) phase.Cu atom in β-Cu_(2Se) lattice was substituted by Bi atom and(Cu,Bi)_(2Se) solid solution formed in the deposited films.The deposited β-Cu_(2-x)Bi_(xSe) films with([Bi]+[Cu])/[Se]2.0 possessed p-typed conductive characteristics.In the range of measured temperature from 25 to 395 ℃,the electrical conductivity decreased and the Seebeck coefficient increased with increasing measured temperature,showing the conductive properties of degenerate or semi-degenerate semiconductors.The carrier concentration and electrical conductivity decreased,but the mobility and Seebeck coefficient increased with increasing Bi content in deposited films at room temperature.The power factor of the Bi-doped films was higher than that of the films without Bi.The power factor of the deposited film increased with Bi content increasing to 225 ℃.Above 225 ℃,the film with doping amount of 0.29at.% Bi had the highest power factor and the power factor of deposited film decreased gradually with further increasing Bi content.The power factor of β-Cu_(2Se) film can be significantly enhanced by doping a proper amount of Bi in films.