Phys. Rev. X 4, 021029 (2014)

Although silicon is an excellent electronic material, it has limitations as an optoelectronic material because of its indirect bandgap and relatively weak absorption of light. Various methods of modifying the band structure and optical properties of silicon have been investigated. Now, researchers in the USA, China and Korea have proposed a new approach — hydrogenation of bilayer silicene, a two-dimensional hexagonal silicon structure. By performing first-principles calculations in conjunction with the cluster-expansion approach, they systematically evaluated the structural and electronic properties of hydrogenated bilayer silicene. The results predict that hydrogenation can significantly enhance the optoelectronic properties of bilayer silicene and yield a widely tunable bandgap. At low hydrogen concentrations, the researchers identified four single- and double-sided hydrogenated bilayer silicene ground-state structures that are predicted to have dipole-allowed direct (or quasi-direct) bandgaps in the range 1–1.5 eV; these structures are thus promising for solar applications. At high hydrogen concentrations, the scientists found three well-ordered double-sided hydrogenated bilayer silicene structures that have bandgaps in the colour ranges of red, green and blue; these structures could potentially be used to fabricate a silicon-based white-light-emitting diode, and hence hold great promise for solid-state lighting.