Theoretical Investigations of Si-Ge Alloys in P42/ncm Phase: First-Principles Calculations

Abstract

The structural, mechanical, anisotropic, electronic and thermal properties of Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase are investigated in this work. The calculations have been performed with an ultra-soft pseudopotential by using the generalized gradient approximation and local density approximation in the framework of density functional theory. The achieved results for the lattice constants and band gaps of P42/ncm-Si and P42/ncm-Ge in this research have good accordance with other results. The calculated elastic constants and elastic moduli of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase are better than that of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/mnm phase. The Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase exhibit varying degrees of mechanical anisotropic properties in Poisson’s ratio, shear modulus, Young’s modulus, and universal anisotropic index. The band structures of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase show that they are all indirect band gap semiconductors with band gap of 1.46 eV, 1.25 eV, 1.36 eV and 1.00 eV, respectively. In addition, we also found that the minimum thermal conductivity κmin of the Si, Si0.667Ge0.333, Si0.333Ge0.667 and Ge in P42/ncm phase exhibit different degrees of anisotropic properties in (001), (010), (100) and (0true1¯0) planes.

Group 14 elements in the Cmcm phase with a direct band structure for photoelectric application

“…Saleev et al [37] proposed six novel Si and Ge allotropes, and the crystal structure, elastic property, and electronic and optical properties of Si and Ge allotropes were studied. This is attributed to the fact that semiconductor alloys could change by indirect band gap to direct band gap or quasi-direct band gap to a certain extent, for example, Si-C alloys, Si-Ge alloys and Ge-Sn alloys [38][39][40][41][42][43][44], to acquire the ideal direct band gap semiconductor material. Fan et al [38] predicted two new Ge allotropes in the hP12 and oC12 phases.…”

Direct and quasi-direct band gap of novel Si-Ge alloys in P-3m1 phase

“…In recent years, the elements of group 14 have attracted more and more attention from researchers . Since semiconductor alloys can be converted from indirect to direct band gaps to some extent, researchers focused on group 14 ele-ment alloys, such as C-Si [23][24][25][26], Si-Ge [26][27][28][29][30][31][32][33][34][35][36][37][38], and Ge-Sn [34,39], to obtain suitable semiconductor materials with direct band gaps. Fan et al [32] studied the physical principles, and found that doping germanium to Si 12 in oC12 and hP12 phases can make its band gap shifted from indirect to direct.…”

P63/mmc-Ge and their Si–Ge alloys with a mouldable direct band gap

“…However, obtaining allotropes of diamond-Si with a direct band gap is difficult, as most are indirect band gaps [7][8][9][10][11][12][13][14][15][16][17][18]. Therefore, researchers in the field have focused on semiconductor alloys, such as C-Si [19,20], Si-Ge [7,19,[21][22][23][24][25][26][27][28][29], and Ge-Sn [28,30], to obtain suitable semiconductor materials with a direct band gap.…”