Two Direct Bandgap Silicon Phases from High-Throughput Structure Screening

Herein, two silicon allotropes (CMMM-Si-20 and CCCA-Si-18) with excellent photoelectronic properties are proposed, based on first-principles calculations. Through the Heyd-Scuseria-Ernzerhof-based band of CMMM-Si-20 and CCCA-Si-18, it is revealed that they are direct bandgap semiconductors with fundamental bandgaps of 0.6373 and 0.7704 eV, respectively, and the direct bandgap properties are robust against the strain. Furthermore, it is found that both CMMM-Si-20 and CCCA-Si-18 exhibit stronger light absorption capacity than diamond silicon (cd-Si) in the visible light region. In the results, it is shown that CMMM-Si-20 and CCCA-Si(18 )are low-energy meta-stable silicon phases, because their energies are only about 0.176 and 0.15 eV atom(-1) higher than that of diamond silicon and lower than that of some predicted and synthesized silicon phases. Their stabilities are confirmed by the calculations of elastic constants, phonon dispersion, and molecular dynamic. Through these findings, it is demonstrated that CMMM-Si-20 and CCCA-Si(18 )are promising candidate silicon materials for solar cells.