Accurate Estimation of Band Offsets in Group IV Polytype Junctions: A First-Principles Study

Abstract

Recent advances in the fabrication of group IV homojunctions made by cubic-diamond (3C) and hexagonal-diamond (2H) phases call for a detailed understanding of the physics underlying their electronic structure. In this work, we employ hybrid density functional theory (hybrid-DFT) calculations to study the structural and electronic properties of Si and Ge polytype junctions. Starting from high-resolution transmission electron microscopy (HRTEM) micrographs of 2H/3C Si nanowires, we build a computational model that takes into account both crystal-phase effects and the length of the junction. We obtain accurate estimations of the magnitudes of the band offsets: In particular, we show that 2H/3C Si interfaces induce a type-II band alignment, whereas the Ge structures exhibit a type-I band offset. Furthermore, both Si and Ge homojunctions have direct gaps that are smaller than those of the bulk 3C phase. Finally, we demonstrate that, in all of the considered systems, varying the thickness of the hexagonal phase...