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首页> 外文期刊>Thin Solid Films >Effect of vacuum annealing on structural, electrical and thermal properties of e-beam evaporated Bi2Te3 thin films
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Effect of vacuum annealing on structural, electrical and thermal properties of e-beam evaporated Bi2Te3 thin films

机译：真空退火对电子束蒸发Bi2Te3薄膜的结构，电和热性能的影响

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Nanocrystalline thin films of a V-VI compound Bi2Te3 are fabricated with uniform thickness by e-beam evaporation at room temperature. The as-deposited films are stoichiometric, monophasic, highly strained and polycrystalline. We studied the effect of vacuum annealing (at a pressure of similar to 3 x 10(-6) mbar) on composition, structure, optical and electrical properties of these films. It is observed that, as the annealing temperature increases (from 100 degrees C to 300 degrees C), the crystallites grow with a preferential orientation along (110) planes with slight increase in the crystallite size from similar to 14 nm to 30 nm. This is associatedwith the breaking of quintuple layers and rearrangement of crystallographic planes in the crystallites with Te rich surface emerging on vacuum annealing as evidenced from the XRD, Raman and high-resolution TEM studies. The direct bandgap (0.116 eV) of as-deposited Bi2Te3 changes from0.092 eV to 0.113 eV on annealing at 100 degrees C to 300 degrees C, respectively. Interestingly, we observe a gradual change from a semiconductor to metallic behavior on annealing the samples from 100 degrees C to 300 degrees C. Such a transition from negative temperature coefficient (NTC) to positive temperature coefficient (PTC) is seen mainly due to the percolation of Te -rich crystallite surfaces, which evolve as the annealing temperature increases. While the films annealed at 200 degrees C and 250 degrees C shows a broad semiconductor to metallic transition at similar to 150 K and 200 K respectively, the thin films annealed at 300 degrees C are found to exhibit complete metallic behavior belowroomtemperature. The electrical property and Seebeck coefficient studieswith power factors in the range of similar to 4 to 12 x 10(-4) W/K-2 m for films annealed above 200 degrees C suggest that the vacuum annealed Bi2Te3 thin films are favorable for thermoelectric applications. (C) 2017 Elsevier B.V. All rights reserved.
机译：通过在室温下通过电子束蒸发制备厚度均匀的V-VI化合物Bi2Te3纳米晶薄膜。沉积的薄膜是化学计量的，单相的，高度应变的和多晶的。我们研究了真空退火（在类似于3 x 10（-6）mbar的压力下）对这些膜的组成，结构，光学和电学性质的影响。可以观察到，随着退火温度的升高（从100摄氏度到300摄氏度），微晶沿着（110）平面以优先取向生长，微晶尺寸从大约14 nm略微增加到30 nm。这与通过X射线衍射，拉曼光谱和高分辨率TEM研究证明的，在真空退火中出现富Te表面的微晶中五层层的破裂和晶体平面的重排有关。沉积后的Bi2Te3的直接带隙（0.116 eV）在100摄氏度至300摄氏度下退火时分别从0.092 eV变为0.113 eV。有趣的是，在将样品从100摄氏度退火到300摄氏度时，我们观察到从半导体到金属行为的逐渐变化。这种从负温度系数（NTC）到正温度系数（PTC）的转变主要是由于渗滤富含Te的微晶表面，其随着退火温度的升高而发展。虽然在200摄氏度和250摄氏度下退火的薄膜分别在150 K和200 K下显示出从半导体到金属的宽泛过渡，但发现在300摄氏度下退火的薄膜在室温以下显示出完全的金属行为。在200摄氏度以上退火的薄膜的电学性质和塞贝克系数研究，功率因数在大约4至12 x 10（-4）W / K-2 m范围内，表明真空退火的Bi2Te3薄膜适合热电应用。 （C）2017 Elsevier B.V.保留所有权利。

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