Nonlinear Concentration-Dependent Electronic and Optical Properties

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Article pubs.acs.org/JPCC

Nonlinear Concentration-Dependent Electronic and Optical Properties of Si1−xGex Alloy Nanowires Yixi Zhang, Gang Xiang,* Gangxu Gu, Rui Li, Duanwei He, and Xi Zhang* Department of Physics and Key Laboratory for Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064, China ABSTRACT: Nonlinear concentration-dependent electronic and optical properties of the Si1−xGex substitutional alloy nanowires are investigated using first-principles calculations. The nonuniform distribution of Ge (or Si) atoms is found, and the resulting orbital hybridization of the inner Ge or Si atoms results in the nonlinear Ge concentration dependence of electronic properties in the Si1−xGex alloy NWs, which suggests an effective approach to modulate band-gap properties of the NWs along all three directions. Moreover, a strong adsorption of solar radiation and a high quantum yield is predicted in (110)-oriented alloy NWs, which implies a great potential of Si1−xGex alloy NWs in the optical electronics applications on nanoscale.

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INTRODUCTION

THEORETICAL BASIS We have performed first-principles calculations within density functional theory (DFT), and the exchange correlation potential has been approximated by generalized gradient approximation (GGA) using PW91 functional in the VASP code. Separation between two closest H atoms between neighboring wires is between 6 and 8 Ǻ to eliminate the interaction. Projected augmented wave (PAW) potentials have been employed, and the Brillouin zone is sampled in the k space within the Monkhorst-Pack scheme by (1 × 1 × 9) mesh points. The energy cutoff for the plane waves is 350 eV, and the convergence for energy is chosen to be 10−5 eV between tow ionic steps. We allow the volume of the supercell to be relaxed as well as the internal coordinates until the Hellmann− Feynman forces are