Tunable Electronic Structures of Hydrogenated Zigzag and Armchair Dumbbell Silicene Nanosheets: A Computational Study

Very recently, zigzag and armchair dumbbell silicene (zd-Si and ad-Si) nanosheets have been identified as the most stable structures of two-dimensional silicon systems. Here, utilizing the first-principle calculations, we have investigated the fully hydrogenated forms of these dumbbell silicene (H-zd-Si and H-ad-Si). It is found that the hydrogenation is an energetically favorable process on the dumbbell silicene, for which the formed structures possess robust mechanical, dynamical, and thermal stabilities. Semiconducting behaviors are well preserved in these H-zd-Si and H-ad-Si nanosheets, which are indirect- and direct-gap semiconductors with larger band gaps than the pristine cases. The gap sizes and band features can be significantly modulated by uniaxial strains, and an indirect-to-direct (direct-to-indirect) band gap transition occurs in the H-zd-Si (H-ad-Si) nanosheet under a small y-axial tensile strain. More interestingly, a ultra high electron mobility is present in the H-ad-Si nanosheet, which reaches up to 3.6/1.5 × 104 cm2/(V s) in the x/y direction. Besides that, the carrier mobility ratio in the H-ad-Si nanosheet is as large as 9.93/15.34 in the x/y direction, which benefits the hole and electron separation. For these dumbbell silicene, a type-II band alignment can be formed between the hydrogenated and pristine nanosheets. In particular, the combined H-ad-Si/ad-Si system will be a promising excitonic solar cell material, whose power conversion efficiency is up to 13–20%. Owing to these peculiar electronic properties, the hydrogenated dumbbell silicene nanosheets are promising nanomaterials for the potential nanoelectric and green-energy applications