具非均勻銀原子摻雜結構之碲化鉍系薄膜熱電傳輸性質研究

碲化鉍系化合物為室溫範圍具有優異表現之熱電材料。優良的熱電材料必須具備高Seebeck係數、高電傳導係數以及低熱傳導係數，而以上性質可透過調控材料中之載子濃度達成。本研究計畫於軟性聚亞醯胺基板上濺鍍P型及N型兩種碲化鉍薄膜，再以電子束蒸鍍法於熱電薄膜上沉積一階梯狀銀擴散疊層，最後經由高溫熱退火處理在碲化鉍薄膜中建立一非均勻擴散區域。研究目的在於探討銀摻雜效應對P型及N型碲化鉍薄膜熱電傳輸性質之影響。研究結果顯示銀原子於熱電薄膜中呈現水平以及垂直兩個方向的不均勻擴散。銀摻雜使P型熱電薄膜載子濃度提升約4.7倍，推測為錯位型缺陷AgSb提供大量電洞所造成。而N型熱電薄膜於銀摻雜後載子濃度則僅小幅提升約1.75倍，推測為系統中過多的Te形成TeBi供體缺陷，抑制AgBi受體缺陷的產生。此外具非均勻銀摻雜之P型熱電薄膜經過掃描Seebeck量測發現Seebeck係數不對稱現象，當熱流方向為銀摻雜端至非銀摻雜端，且探針針距為5.3 mm時，偵測最大Seebeck係數285 µV/k、最大輸出電流5.41 µA以及最大輸出功率密度(power density)為10.5 nW/cm2。而N型熱電薄膜則無明顯差異，推測需於摻雜端以及非摻雜端建立足夠之載子濃度差異，才可產生Seebeck係數不對稱現象。

關鍵字

熱電材料；薄膜；碲化鉍；銀摻雜；擴散

並列摘要

Bismuth telluride has been considered as a promising candidate for thin-film thermoelectric (TE) devices due to its superior thermoelectric properties at room temperature regime. Generally, a good thermoelectrics requires a large Seebeck coefficient, a high electrical conductivity and a low thermal conductivity, which can be achieved by optimization of carrier concentration. In this study, both P-type Bi-Sb-Te and N-type Bi-Se-Te thin films were deposited on polyimide substrates by RF magnetron sputtering. A step-like Ag overlayer was evaporated partially on top of the TE films using e-gun deposition. Silver atoms were driven into the TE films by thermal annealing to form a non-uniform doping profile. The research goal is to investigate the effect of Ag doping on thermoelectric transport properties of P- and N-type Bi-Te thin films. The results show that Ag elements have non-uniform distributions in both in-plane and out-of-plane directions of TE thin films. The Ag doping results in 4.7 times increase of carrier concentration in P-type films and 1.75 times increase in N-type films. It suggests that AgSb acceptor-like defects provide large amount of hole carriers in P-type films, while the excessive Te atoms occupy Bi site by forming TeBi donor-like defects counterbalances the contribution of AgBi defects in N-type films. The scanning Seebeck results reveal an asymmetric Seebeck effect in the P-type films. The P-type films with Ag doping achieve a maximum Seebeck coefficient of 285 µV/k, an output current of 5.41 µA and a power density of 10.5 nW/cm2 when heat flows in the direction from high to low doping region of P-type films with a distance between two probes of 5.3 mm. The N-type films with Ag doping do not show obviously asymmetric effect, which is likely attributed to small difference in carrier concentration between doped and non-doped region.

並列關鍵字

thermoelectrics ； thin films ； bismuth telluride ； sliver-doping ； diffusion

參考文獻

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具非均勻銀原子摻雜結構之碲化鉍系薄膜熱電傳輸性質研究

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