Continuous tuning of band gap by strain engineering in new predicted 13H-Si allotrope

Abstract

Diamond silicon and most of its allotropes have indirect band gaps that do not allow electrons to propagate directly between the valence and conduction band edges due to momentum mismatch, limiting their performance and efficiency in optoelectronic devices. With the rapid development of the optoelectronic industry, searching for new silicon allotropes with adjustable and/or direct band gap has become increasingly urgent. Here, we predict five new silicon allotropes 13H-Si with continuously tunable band gap, high mechanical, dynamic and thermal stability under tensile strain. As expected, besides their adjustable band gaps in a wide range (0.80–1.30 eV), the indirect-to-direct band gap transition can be achieved in these predicted silicon allotrope 13H-Si under tensile strain (4.5–9.0 %) along a- and b-axis. Especially, these predicted 13H-Si not only demonstrate the stronger visible light absorption ability than diamond silicon, but also show the enhanced absorption intensity under axial strain. The current research not only enriches the types of silicon allotropes, but also accumulates data for the application of silicon materials in the field of solar photovoltaics.