arXiv 1603.048022016-03-15cond-mat.mtrl-sci

Ge $_{1-x}$ Sn $_x$中的两个能隙跃迁：非替位复合缺陷的影响

The two gap transitions in Ge$_{1-x}$Sn$_x$: effect of non-substitutional complex defects

J. D. Querales-Flores, C. I. Ventura, J. D. Fuhr, R. A. Barrio

备注：: 11 pages, 9 Figures
发表信息：: Journal of Applied Physics 120, 105705 (2016)
DOI：: 10.1063/1.4962381

摘要：

Ge $_{1-x}$ Sn $_{x}$中非取代的$β$-Sn缺陷的存在通过发射沟道实验证实[Decoster等人，Phys.Rev.B81，155204（2010）]，其确立了尽管大部分Sn以替代方式（$α$ -Sn）进入Ge晶格中，但第二显著部分对应于分裂空位构型中的Sn-空位缺陷复合物（$β$ -Sn），这与我们先前的理论研究一致[Ventura等人，B79，155202（2009）]。在这里，我们提出了我们的电子结构计算的Ge $_{1-x}$ Sn $_{x}$，包括取代$α$ -Sn以及非取代$β$ -Sn缺陷。为了在这种多轨道合金问题的电子结构计算中包括非替代复合缺陷的存在，我们扩展了Jenkins和Dow [Jenkins和Dow，Phys.Rev.B36，7994（1987）]对纯替代合金的方法。我们采用了一个有效的替代两个网站集群相当于真正的非替代$β$ -Sn缺陷，这是由格林函数计算确定。然后，我们计算的电子结构的有效合金纯粹的替代缺陷，嵌入在晶格中的有效替代集群。我们的研究结果描述了两个过渡的基本间隙的锗$_{1-x}$锡$_{x}$作为总锡浓度的函数：即从间接到直接的间隙，第一，和金属化过渡在较高的$x$。他们还强调了$β$ -Sn在降低对应于该合金的直接带隙相的浓度范围中的作用，这对于光电子应用是有意义的。

英文摘要：

The existence of non-substitutional $β$-Sn defects in Ge$_{1-x}$Sn$_{x}$ was confirmed by emission channeling experiments [Decoster et al., Phys. Rev. B 81, 155204 (2010)], which established that although most Sn enters substitutionally ($α$-Sn) in the Ge lattice, a second significant fraction corresponds to the Sn-vacancy defect complex in the split-vacancy configuration ( $β$-Sn ), in agreement with our previous theoretical study [Ventura et al., Phys. Rev. B 79, 155202 (2009)]. Here, we present our electronic structure calculation for Ge$_{1-x}$Sn$_{x}$, including substitutional $α$-Sn as well as non-substitutional $β$-Sn defects. To include the presence of non-substitutional complex defects in the electronic structure calculation for this multi-orbital alloy problem, we extended the approach for the purely substitutional alloy by Jenkins and Dow [Jenkins and Dow, Phys. Rev. B 36, 7994 (1987)]. We employed an effective substitutional two-site cluster equivalent to the real non-substitutional $β$-Sn defect, which was determined by a Green's functions calculation. We then calculated the electronic structure of the effective alloy purely in terms of substitutional defects, embedding the effective substitutional clusters in the lattice. Our results describe the two transitions of the fundamental gap of Ge$_{1-x}$Sn$_{x}$ as a function of the total Sn-concentration: namely from an indirect to a direct gap, first, and the metallization transition at higher $x$. They also highlight the role of $β$-Sn in the reduction of the concentration range which corresponds to the direct-gap phase of this alloy, of interest for optoelectronics applications.

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