The discovery of stable two-dimensional (2D) semiconductors with exotic electronic properties is crucial to the future electronic technologies. Using the first-principles calculations, we predict the monolayered Silicon- and Germanium-monopnictides as a new class of semiconductors owning excellent dynamical and thermal stabilities, prominent anisotropy, and high possibility of experimental exfoliation. These semiconductors, including the monolayered SiP, SiAs, GeP, and GeAs, possess wide bandgaps of 2.08-2.64 eV obtained by hybrid functional calculation. Under small uniaxial strains (-2 to 3%), dramatic modulations of their band structures are observed, and furthermore, all the 2D monolayers (MLs) can be transformed between indirect and direct semiconductors. The monolayered GeAs and SiP exhibits extraordinary optical absorption in the range of visible and ultraviolet (UV) light spectra, respectively. The exfoliation energies of these monolayers are comparable to graphene, implying a strong probability of successful fabrication by mechanical exfoliation. These intriguing properties of the monolayered silicon- and germanium-monopnictides, combined with their highly stable structures, offer tremendous opportunities for electronic and optoelectronic devices working under UV-visible spectrum.
Searching for new van der Waals (vdW) heterostructure with novel electronic and optical properties is of great interest and importance for the next generation of devices. By using first-principles calculations, we show that the electronic and optical properties of the arsenene/CN vdW heterostructure can be effectively modulated by applying vertical strain and external electric field. Our results suggest that this heterostructure has an intrinsic type-II band alignment with an indirect bandgap of 0.16 eV, facilitating the separation of photogenerated electron-hole pairs. The bandgap in the heterostructure can be tuned from 0-0.35 eV via the strain, experiencing an indirect-to-direct bandgap transition. Moreover, the bandgap of the heterostructure varies linearly with respect to a moderate external electric field, and the semiconductor-to-metal transition can be realized in the presence of a strong electric field. The calculated band alignment and the optical absorption reveal that the arsenene/CN heterostructure could present excellent light-harvesting performance. Our designed vdW heterostructure is expected to have great potential applications in nanoelectronic devices and photovoltaics.
Electroabsorption of strained-layer Inx Ga1−x As/GaAs superlattice structures grown by molecular beam epitaxy on GaAs substrates was experimentally investigated. Its spectral characteristics were found to be similar to those of Franz–Keldysh electroabsorption of bulk semiconductor materials, and suggest that the widths of ground-state electron and hole minibands might be larger than the maximum tilt of the potential well caused by an applied voltage. We attribute the electroabsorption of such superlattices to photon-assisted tunneling between ground-state electron and heavy hole minibands.
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