First-principles study of the dependence of silicon electronic transport properties on the crystallographic growth

Abstract

Differences in the electronic transport properties of two polymorphs of bulk silicon due to the crystallographic direction are investigated theoretically. The calculations are performed in two steps: first an optimized geometry for two polymorphs of silicon (cubic diamond and hexagonal diamond) is obtained using DFT calculations, and then the transport relations of four directions (<001>, <110> and <111> for diamond and <001> for hexagonal) are obtained using NEGF approach. SIESTA and TranSIESTA simulation codes are used in the calculations correspondingly. The electrodes are chosen to be the same as the central region where transport is studied, eliminating current quantization effects due to contacts and focusing the electronic transport study to the intrinsic structure of the material. By varying chemical potential in the electrode regions, an I-V curve is traced for each particular configuration. Conductance in silicon bulk shows certain dependence in the crystallographic direction, in agreement with the different behavior of silicon nanowires due to their growth direction. The study of electronic and transport properties in silicon nanowires is interesting because they are promising candidates as bridging pieces in nanoelectronics.