PbTe低维结构共溅生长及其热电性能研究

发布时间：2018-03-31 02:38

  本文选题：PbTe　切入点：纳米结构　出处：《浙江师范大学》2015年硕士论文

【摘要】：近年来研究表明热电材料的纳米化和低维化可以有效的提高热电优值ZT系数。纳米结构的界面可以有效地散射声子,降低材料的热导率,同时利用界面对低能电子的过滤以及量子尺寸效应带来的能带的改变可以实现功率因子的改善。碲化铅(PbTe)是一种中等温区非常重要的半导体热电材料。PbTe基的量子点超晶格结构其热电优值在550K达到3左右,使得这类纳米低维结构引起了人们极大的关注。本文利用离轴共溅方法生长了不同纳米结构的PbTe薄膜及其低维PbTe/CdTe量子阱,并对其热电性能进行了研究。针对薄膜纳米结构的特点,设计了一种薄膜热电测量的装置,实现了薄膜Seebeck系数和电导率的准确测量。通过改变衬底温度(Ts=220℃、250℃,285℃、320℃)和Te的溅射速率(0.06A/s、 0.13A/s、0.4A/s),制备了各种纳米结构特征的PbTe薄膜,并对各种纳米结构随厚度的演化进行观察和分析。在此基础上,制备了高质量的PbTe/CdTe量子阱,开展了不同周期结构的PbTe/CdTe量子阱热电性能测量(势垒层厚度为4nnm、 14nm、28nm,势阱层厚度为16nm、26nm、36nm,周期数N=1、5、15)主要研究内容如下所示：1：在低Te溅射速率条件下(0.06A/s), PbTe/BaF2薄膜表面分布大量三角金字塔形,金字塔的尺寸为150～200nm,高宽比为1：2。三角金字塔形的形成与离轴和低碲速率下共溅导致的柱状生长有关。金字塔形貌随厚度演化研究表明,膜厚为27nm时存在各种晶向的纳米岛,随厚度增加不同晶向纳米岛相互竞争生长,膜厚达到260mm沿(111)晶向择优取向柱状生长,最终在薄膜表面形成三角金字塔形。2：Te溅射速率的升高(0.13A/s、0.4A/s),三角金字塔演变为截角八面体、花形、三角坑和三角盘。Te溅射速率为0.13A/s,衬底温度为220℃, PbTe/BaF2薄膜表面分布大量1um左右的花形结构。在衬底温度为250℃,得到平整的表面和微米级的截角八面体。当衬底温度升高到285℃,薄膜表面为截角八面体和三角盘。随着Te溅射速率升高到0.4A/s,薄膜表面为三角坑和三角盘结构,薄膜表面形貌的演变与{111}面和{100}面生长速率有关。Te元素比例的增加使得{111}面和{100}面生长速率的比值增大。3：不同结构的PbTe/CdTe量子阱测量显示在300-600K范围内,电导率随温度升高而增加,Seebeck系数随着温度升高而变小。这种变化趋势表明量子阱中晶界相关的激活能对热电性能产生重要影响。Seebeck系数随着PbTe势阱层厚度增加而增加。随CdTe势垒宽度增加而减小。同时,量子阱周期增加使得Seebeck系数减小。优化结构的PbTe/CdTe量子阱室温Seebeck系数可以达到513μV/K。在530K温度范围,PbTe/CdTe量子阱Seebeck系数存在p-n型转变。其热循环测试表明这种转变与500K附近量子阱结构的改变以及Te的偏析有关。
[Abstract]:Recent studies have shown that nanocrystalline and low dimensional thermoelectric materials can effectively improve the excellent value of thermoelectric ZT coefficient.The interface of nanostructure can effectively scatter phonons and reduce the thermal conductivity of materials. At the same time, the improvement of power factor can be realized by filtering low energy electrons at the interface and changing the energy band caused by quantum size effect.Lead telluride (PbTe) is a very important semiconductor thermoelectric material. PbTe based quantum dot superlattice has a thermoelectric excellent value of about 3 at 550 K, which has attracted much attention.In this paper, PbTe thin films with different nanostructures and their low-dimensional PbTe/CdTe quantum wells have been grown by off-axis co-splashing method, and their thermoelectric properties have been investigated.According to the characteristics of thin film nanostructures, a thermoelectric measurement device is designed to measure the Seebeck coefficient and conductivity accurately.PbTe thin films with various nanostructures were prepared by changing the substrate temperature and the sputtering rate of Te: 0.06A / s, 0.13A / s = 0.4A / s, respectively. The evolution of various nanostructures with thickness was observed and analyzed.On this basis, high quality PbTe/CdTe quantum wells were prepared.The measurements of thermoelectric properties of PbTe/CdTe quantum wells with different periodic structures have been carried out (the barrier layer thickness is 4nnm, the potential well layer thickness is 4nnm, the potential well layer thickness is 16nm ~ 26nm ~ (-1) 36nm, and the period number is N ~ (1)). The main research contents are as follows: at low Te sputtering rate, 0.06A / s / s, the surface distribution of PbTe/BaF2 thin films is large.Measuring triangular pyramids,The pyramid is 150 / 200 nm in size and 1: 2 in aspect ratio.The formation of triangular pyramid is related to the columnar growth induced by co-splashing at off-axis and low tellurium rates.The morphologies of pyramids evolved with the thickness of 27nm. The results showed that there were various nanowires in different directions when the film thickness was 27nm, and the films grew in competition with each other with the thickness increasing, and the film thickness reached to the preferred columnar growth of 260mm along the crystal direction.Eventually, a triangular pyramid. 2: Te sputter rate increases 0.13 A / s 0. 4 A / S, and the triangular pyramid evolves into a truncated octahedron, a flower shape.The sputtering rate is 0.13A / s and the substrate temperature is 220 鈩，

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