本文選題：PbTe　切入點(diǎn)：納米結(jié)構(gòu)　出處：《浙江師范大學(xué)》2015年碩士論文

【摘要】：近年來研究表明熱電材料的納米化和低維化可以有效的提高熱電優(yōu)值ZT系數(shù)。納米結(jié)構(gòu)的界面可以有效地散射聲子,降低材料的熱導(dǎo)率,同時(shí)利用界面對低能電子的過濾以及量子尺寸效應(yīng)帶來的能帶的改變可以實(shí)現(xiàn)功率因子的改善。碲化鉛(PbTe)是一種中等溫區(qū)非常重要的半導(dǎo)體熱電材料。PbTe基的量子點(diǎn)超晶格結(jié)構(gòu)其熱電優(yōu)值在550K達(dá)到3左右,使得這類納米低維結(jié)構(gòu)引起了人們極大的關(guān)注。本文利用離軸共濺方法生長了不同納米結(jié)構(gòu)的PbTe薄膜及其低維PbTe/CdTe量子阱,并對其熱電性能進(jìn)行了研究。針對薄膜納米結(jié)構(gòu)的特點(diǎn),設(shè)計(jì)了一種薄膜熱電測量的裝置,實(shí)現(xiàn)了薄膜Seebeck系數(shù)和電導(dǎo)率的準(zhǔn)確測量。通過改變襯底溫度(Ts=220℃、250℃,285℃、320℃)和Te的濺射速率(0.06A/s、 0.13A/s、0.4A/s),制備了各種納米結(jié)構(gòu)特征的PbTe薄膜,并對各種納米結(jié)構(gòu)隨厚度的演化進(jìn)行觀察和分析。在此基礎(chǔ)上,制備了高質(zhì)量的PbTe/CdTe量子阱,開展了不同周期結(jié)構(gòu)的PbTe/CdTe量子阱熱電性能測量(勢壘層厚度為4nnm、 14nm、28nm,勢阱層厚度為16nm、26nm、36nm,周期數(shù)N=1、5、15)主要研究內(nèi)容如下所示：1：在低Te濺射速率條件下(0.06A/s), PbTe/BaF2薄膜表面分布大量三角金字塔形,金字塔的尺寸為150～200nm,高寬比為1：2。三角金字塔形的形成與離軸和低碲速率下共濺導(dǎo)致的柱狀生長有關(guān)。金字塔形貌隨厚度演化研究表明,膜厚為27nm時(shí)存在各種晶向的納米島,隨厚度增加不同晶向納米島相互競爭生長,膜厚達(dá)到260mm沿(111)晶向擇優(yōu)取向柱狀生長,最終在薄膜表面形成三角金字塔形。2：Te濺射速率的升高(0.13A/s、0.4A/s),三角金字塔演變?yōu)榻亟前嗣骟w、花形、三角坑和三角盤。Te濺射速率為0.13A/s,襯底溫度為220℃, PbTe/BaF2薄膜表面分布大量1um左右的花形結(jié)構(gòu)。在襯底溫度為250℃,得到平整的表面和微米級(jí)的截角八面體。當(dāng)襯底溫度升高到285℃,薄膜表面為截角八面體和三角盤。隨著Te濺射速率升高到0.4A/s,薄膜表面為三角坑和三角盤結(jié)構(gòu),薄膜表面形貌的演變與{111}面和{100}面生長速率有關(guān)。Te元素比例的增加使得{111}面和{100}面生長速率的比值增大。3：不同結(jié)構(gòu)的PbTe/CdTe量子阱測量顯示在300-600K范圍內(nèi),電導(dǎo)率隨溫度升高而增加,Seebeck系數(shù)隨著溫度升高而變小。這種變化趨勢表明量子阱中晶界相關(guān)的激活能對熱電性能產(chǎn)生重要影響。Seebeck系數(shù)隨著PbTe勢阱層厚度增加而增加。隨CdTe勢壘寬度增加而減小。同時(shí),量子阱周期增加使得Seebeck系數(shù)減小。優(yōu)化結(jié)構(gòu)的PbTe/CdTe量子阱室溫Seebeck系數(shù)可以達(dá)到513μV/K。在530K溫度范圍,PbTe/CdTe量子阱Seebeck系數(shù)存在p-n型轉(zhuǎn)變。其熱循環(huán)測試表明這種轉(zhuǎn)變與500K附近量子阱結(jié)構(gòu)的改變以及Te的偏析有關(guān)。
[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，

本文編號(hào)：1688821