Beta矽化鐵塊材的合成及電性量測

Abstract

β-FeSi2是相當吸引人的材料，具高熱電轉換效率，對可見光有高的吸收係數，容易與Si的製程整合，文獻上顯示其具有熱能隙(Thermal energy gap)約在0.87eV至0.95eV之間。在本論文中我們嘗試以不同的合成方法及不同的退火條件，合成β-FeSi2。發現在800℃的退火溫度，1000小時的退火時間，以及快速冷卻的方法，會有較佳的熱電轉換效率，而且在材料中摻雜銅，在熱電轉換效率的表現上也得到不錯的結果。猜測較高的熱電轉換效率是因為ε相與α相及Si在退火後或摻雜銅時，易轉換成β-FeSi2。我們也以粉末X-RAY繞射、拉曼散射量測、SEM與EPMA來分析材料的合成品質、組成與成分。此外，以變溫電阻率的量測去觀察β-FeSi2的導電特性，得到它的熱能隙約在0.82eV至0.88eV之間；在低溫區(100K至200K)，電阻率和溫度間的關係符合Mott定律，暗示材料內含有高濃度雜質和缺陷。

β-FeSi2 is an attractive material because of its high thermoelectric power，high absorption coefficient of visible light，and the integrating on silicon substrate﹒The thermal energy gap ofβ-FeSi2 has been reported 0.87eV－0.95eV in some literatures[1][2]﹒In this research，we synthesized and annealed theβ-FeSi2 in some different conditions﹒Theβ-FeSi2 was observed higher thermoelectric power in the condition that the syntheticβ-FeSi2 was quenched，and then annealed at 800℃，sustained 1000 hours﹒We also found that the copper-dopedβ-FeSi2 performed higher thermoelectric power﹒The higher thermoelectric power could be becauseβ-FeSi2 was formed fast fromε－FeSi and α－Fe2Si5 after annealing or doping copper﹒Structural characterizations were made by X-ray diffraction，Raman scattering，scanning electron microscopy and electron probe microanalyzer﹒Further more，ther result of measurement of resistivity as a function of reciprocal temperature is shown with a thermal energy gap 0.82eV－0.88eV﹒At low temperature(100K－200K)，the temperature dependence of the resistivity matched well with Mott's exp(To/T)^(1/4)law，indicating high impurity and defect in our materials﹒