Thickness-dependent electronic transport induced by in situ transformation of point defects in MBE-grown Bi2Te3 thin films

作者：Zhang, Min; Liu, Wei^*; Zhang, Cheng; Qiu, Junhao; Xie, Sen; Hua, Fuqiang; Cao, Yu; Li, Zhi; Xie, Hongyao; Uher, Ctirad; Tang, Xinfeng^*

来源：Applied Physics Letters, 2020, 117(15): 153902.

DOI：10.1063/5.0025828

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Interactions among various film growth parameters, such as the substrate temperature (T-sub), film thickness (d), and composition, play a crucial role in controlling the type and density of the intrinsic point defects. In turn, the point defects modulate and control electronic transport properties of Bi2Te3 films. We have grown n-type Bi2Te3 films with different d by molecular beam epitaxy at different T-sub. The formation of point defects was analyzed by a combined use of angle-resolved photoelectron spectroscopy (ARPES) and electronic transport measurements. Two important findings were made: (i) the negatively charged vacancies,
V
Te
center dot center dot initially the dominant intrinsic defects, transform gradually during the growth process into positively charged anti-site defects,
B
i
Te
', driven by thermal annealing from a continuously heated substrate; and (ii) from the film's surface into the inner strata of the film, the density of
V
Te
center dot center dot decreases while the density of
B
i
Te
; increases, leading to a gradient of vacancies and anti-site defects along the film growth direction. As a result, the electron density in Bi2Te3 films decreases monotonically with increasing d. Moreover, elevating T-sub leads to a more significant in situ annealing effect and an eventual onset of intrinsic excitations that deteriorates electronic transport properties. The thinnest Bi2Te3 film (16nm) grown at T-sub=245 degrees C has the highest electron concentration of 2.03x10(20)cm(-3) and also the maximum room temperature power factor of 1.6 mW m(-1) K-2 of all grown epitaxial films. The new insights regarding the defect formation and transformation pave the way for further optimization of electronic transport properties of n-type Bi2Te3-based films.

• 单位
  武汉理工大学; 西北大学