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Thermoelectric properties of bismuth-selenide films with controlled morphology and texture grown using pulsed laser deposition

机译:通过脉冲激光沉积生长可控制形态和织构的硒化铋薄膜的热电性能

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摘要

Polycrystalline, thermoelectric thin films of bismuth selenide (Bi_2Se_3) were grown on SiO_2/Si (111) substrates, using pulsed laser deposition (PLD). Bi_2Se_3 films with highly c-axis-oriented and controlled textures were fabricated by maintaining the helium gas pressure (P) between 0.7 and 173 Pa and the substrate temperature (T_s) between 200 and 350 ℃. The carrier concentration (n) of films decreased with increasing P, which was attributed to the increase of Se concentration from Se deficiency (P ≤ 6.7 Pa) to stoichiometry to slight Se enrichment (P ≥40 Pa). The Seebeck coefficient (S) was enhanced considerably because of the reduction in n, following the S~n~(-2/3) relation approximately. The average grain size increased from approximately 100 to 500 nm when T_s was raised from 200 to 350 ℃, resulting in enhanced carrier mobility (μ) and electrical conductivity (σ) and a reduced full width at half maximum of (006) peaks. The shape of grains transformed from rice-like at T_s of 200-250℃ to layered-hexagonal platelets (L-HPs) or super-layered flakes (S-LFs) at T_s of 300-350 ℃. Films that were grown at 300 ℃ and 40 Pa and contained highly c-axis oriented L-HPs possessed the highest power factor (PF=S~2σ), which reached 5.54μWcm~(-1) K~(-2), where S = 75.8μV/K and σ = 963.8 S cm~(-1).
机译:使用脉冲激光沉积(PLD)在SiO_2 / Si(111)衬底上生长硒化铋(Bi_2Se_3)的多晶热电薄膜。通过将氦气压力(P)维持在0.7至173 Pa之间,并将衬底温度(T_s)维持在200至350℃之间,制造出具有高度c轴取向和可控纹理的Bi_2Se_3薄膜。薄膜的载流子浓度(n)随着P的增加而降低,这归因于Se浓度从Se缺乏(P≤6.7 Pa)到化学计量比到Se略微富集(P≥40Pa)。由于n的减少,塞贝克系数(S)大大提高,大致遵循S〜n〜(-2/3)关系。当T_s从200℃提高到350℃时,平均晶粒尺寸从约100nm增加到500nm,从而导致载流子迁移率(μ)和电导率(σ)提高,全峰宽度减小了(006)峰的一半。籽粒的形状从200-250℃的T_s转变为米状,再到300-350℃的T_s转变为层状六方血小板(L-HPs)或超薄薄片(S-LFs)。在300℃和40 Pa的温度下生长并带有高度c轴取向的L-HPs的薄膜具有最高的功率因数(PF = S〜2σ),达到5.54μWcm〜(-1)K〜(-2),其中S =75.8μV/ K,σ= 963.8 S cm〜(-1)。

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