Interactions among various film growth parameters, such as the substrate temperature (Tsub), 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 Tsub. 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 · ·, 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 · · 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 Tsub 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 (16 nm) grown at Tsub = 245 °C has the highest electron concentration of 2.03 × 1020 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.

中文翻译：

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由 MBE 生长的 Bi2Te3 薄膜中点缺陷的原位转变引起的与厚度相关的电子输运

各种薄膜生长参数之间的相互作用，如衬底温度 (Tsub)、薄膜厚度 (d) 和成分，在控制本征点缺陷的类型和密度方面起着至关重要的作用。反过来，点缺陷调节和控制 Bi2Te3 薄膜的电子传输特性。我们已经通过分子束外延在不同 Tsub 下生长了具有不同 d 的 n 型 Bi2Te3 薄膜。通过结合使用角分辨光电子能谱 (ARPES) 和电子输运测量来分析点缺陷的形成。有两个重要发现：(i) 带负电的空位 V Te · · 最初是主要的固有缺陷，在生长过程中逐渐转变为带正电的反位缺陷 B i Te '，由热退火驱动连续加热基板；(ii) 从薄膜表面到薄膜内层，V Te · · 的密度降低，而 B i Te ' 的密度增加，导致沿薄膜生长方向的空位和反位缺陷梯度. 因此，Bi2Te3 薄膜中的电子密度随着 d 的增加而单调减少。此外，提高 Tsub 会导致更显着的原位退火效应，并且最终会出现使电子传输特性恶化的内在激发。在 Tsub = 245 °C 下生长的最薄的 Bi2Te3 膜（16 nm）具有最高的电子浓度 2.03 × 1020 cm-3，并且在所有生长的外延膜中的最大室温功率因数为 1.6 mW m-1 K-2。