Insights into the unusual semiconducting behavior in low-dimensional boron.

Elementary semiconductors are rare and attractive, especially for low-dimensional materials. Unfortunately, most of the boron nanostructures have been found to be metallic, despite their typical semiconducting bulk structure. Herein, we propose a general recipe to realize low-dimensional semiconducting boron. This unusual semiconducting behavior is attributed to charge transfer and electron localization, induced by symmetry breaking that divides boron atoms into cations and anions. In addition, it is feasible to accomplish band gap engineering by rationally designing various structures. Importantly, the low-dimensional semiconducting boron allotropes are predicted to be an excellent solar-cell material with a power conversion efficiency of up to 22%, paving the way for their promising optoelectronic application.

Two-Dimensional Semiconducting Boron Monolayers.

The two-dimensional boron monolayers were reported to be metallic both in previous theoretical predictions and experimental observations. Unexpectedly, we have first found a family of boron monolayers with the novel semiconducting property as confirmed by the first-principles calculations with the quasi-particle G0W0 approach. We demonstrate that the connected network of hexagonal vacancies dominates the gap opening for both the in-plane s+px,y and pz orbitals, with which various semiconducting boron monolayers are designed to realize the band gap engineering for the potential applications in electronic devices. The semiconducting boron monolayers in our predictions are expected to be synthesized on the proper substrates, due to the similar stabilities to the ones observed experimentally.