能障散射效應對Bi0.5Sb1.5Te3薄膜熱電性質影響之研究

A study of grain boundary scattering effect on thermoelectric properties of Bi0.5Sb1.5Te3 thin films

王亞帆(Ya-Fan Wang)

指導教授 ： 廖建能

國立清華大學/工學院/材料科學工程學系/碩士(2007年)

https://doi.org/10.6843/NTHU.2007.00694

摘要

本研究主要探討晶界能障散射效應對Bi0.5Sb1.5Te3薄膜材料熱電性質的影響。Bi0.5Sb1.5Te3合金材料為目前在室溫下最佳的p型熱電材料，本實驗利用磁控濺鍍法在不同製程溫度製備不同晶粒尺寸的Bi0.5Sb1.5Te3薄膜試片。實驗結果顯示隨著製程溫度由室溫上昇到200ºC，晶粒大小從25nm增加到100nm，而小晶粒尺寸的Bi0.5Sb1.5Te3薄膜試片其Seebeck係數高達280μV/K，較大晶粒的薄膜試片高約50%。藉由薄膜載子濃度、遷移率與電阻率的量測結果與載子傳輸理論模型相比較，推測此Seebeck係數的提升應來自於小晶粒尺寸薄膜試片具有較大比例的晶界能障散射效應所致。此小晶粒尺寸薄膜試片雖具有較高的Seebeck係數，但電阻率亦偏高。因此後續透過高溫短時間和低溫長時間兩種退火方式來改善室溫下鍍製的Bi0.5Sb1.5Te3薄膜試片電阻率。實驗結果顯示室溫鍍製的薄膜試片經225℃退火5分鐘後，電阻率大幅降為6.3 mΩ-cm，Seebeck係數微幅下降至210μV/K，退火後薄膜試片的最佳功率因子為7 10-4W/m-K2。

關鍵字

Bi2Te3 ； 熱電材料 ； 晶粒尺寸

並列摘要

The effect of grain boundary potential scattering on thermoelectric properties of Bi0.5Sb1.5Te3 thin films has been investigated. Bi0.5Sb1.5Te3 is known to be the best p-type thermoelectric material at the room temperature regime. In this study, the Bi0.5Sb1.5Te3 thin films of various grain sizes were deposited at different substrate temperatures by the magnetron sputter deposition method. As the deposition temperature increases from room temperature to 200 ºC, the grain size of the sputtered Bi0.5Sb1.5Te3 thin films increase from 25nm to 100nm. The sputtered thin film with the smallest grain size has a very high Seebeck coefficient of 280 μV/K, which is 50% higher than that of the film of 100 nm in grain size. By comparing the measured carrier concentration, mobility, resistivity with the theoretical predictions from the carrier transport model, it is suggested that the enhancement of Seebeck coefficient for the sputtered Bi0.5Sb1.5Te3 thin films is mainly attributed to the effect grain boundary potential scattering. Since the as-deposited Bi0.5Sb1.5Te3 thin films have high electrical resistivity, two different thermal treatments, high temperature/short duration and low temperature/long duration, have been employed to reduce the resistivity of the sputtered Bi0.5Sb1.5Te3 thin films. It is found that the Bi0.5Sb1.5Te3 thin films has the lowest resistivity of 6.3mΩ-cm and a moderately reduced Seebeck coefficient of 210μV/K, leading to the highest power factor of 7 10-4W/m-K2 after annealing at 225 ºC for 5 minutes.

參考文獻

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[4] G. S. Nolas, J. Sharp and H. J. Goldsmid, “Thermoelectrics”, Chap. 2, p.40

[6] G. S. Nolas, J. Sharp and H. J. Goldsmid, “Thermoelectrics”, Chap. 5 p.118