title: Composition-dependent band gaps and indirect-direct band gap transitions of group-IV semiconductor alloys.
abstract: We used the coherent potential approximation to investigate the band structures of group-IV semiconductor alloys, including Si(x)Ge(1-x), Ge(1-y)Sn(y) and Si(x)Ge(1-x-y)Sn(y). The calculations for Si(x)Ge(1-x) prove the reliability and accuracy of the method we used. For Ge(1-y)Sn(y), the direct band gap optical bowing parameter we obtained is 2.37 eV and the indirect-direct band gap transition point is at y = 0.067, both consistent with the existing experimental data. For Si(x)Ge(1-x-y)Sn(y), with the increase of the Si concentration, the compositional dependency of the band gap becomes complex. An indirect-direct band gap transition is found in Si(x)Ge(1-x-y)Sn(y) in the range of 0 < x≤ 0.20, and the indirect-direct crossover line in the compositional space has the quadratic form of y = 3.4x(2) + 1.11x + 0.07, not the linear form as suggested before. Furthermore, for the Ge lattice-matched alloy Ge(1-x()Si0.79Sn0.21)(X), our results show that those with 0.18 < X < 0.253 have band gaps larger than 0.8 eV at room temperature.
authors.affiliation: Shanghai Ultra-Precision Optical Manufacturing Engineering Center, Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China. junzhuang@fudan.edu.cn.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhu
authors.forename: Jiamin
authors.initials: J
authors.lastname: Xiao
authors.forename: Haibin
authors.initials: H
authors.lastname: Sun
authors.forename: Yue
authors.initials: Y
authors.lastname: Hu
authors.forename: Ronggen
authors.initials: R
authors.lastname: Cao
authors.forename: Yin
authors.initials: Y
authors.lastname: Wang
authors.forename: Li
authors.initials: L
authors.lastname: Zhao
authors.forename: Jun
authors.initials: J
authors.lastname: Zhuang