Characterization of electronic and optical properties of doped GeSe monolayer using first principles calculation

Abstract

Of late, group-IV monochalcogenides, isoelectronic to phosphorene with similar orthorhombic puckered structure, have drawn numerous interest due to their tunable isoelectronic properties, giant piezoelectricity etc. Among the members of this family, GeSe, a material with small carrier effective mass and intriguing anisotropic properties, has shown great potential in optoelectronic and thermoelectric devices. Monolayer GeSe is an intrinsic multiferroic material with small thermal conductivity and high electrical conductivity indicating its potential application in information storage devices. A few layers to monolayer GeSe have been successfully fabricated and they have been extensively used in photodetectors, phototransistors, and solar cells. On the other hand, substitutional doping has traditionally been used to modulate the existing properties of semiconductors and introduce new exciting properties, especially in two-dimensional materials. Considering these, in this work, we have investigated the impact of substitutional doping (using group III, IV, V, and VI dopants) on the structural, electronic, spin, and optical properties of GeSe monolayer by using first-principles calculations based on density functional theory. The change in the structural parameters are calculated and a possibility of the formation of dangling bonds has been found when Ge is substituted with group VI dopants. Our calculated binding energies of the doped systems also support their stability and hence the feasibility of physical realization. The results further suggest that switching between metallic and semiconducting states of GeSe monolayer can be controlled by dopant atoms with a different number of valence electrons. The band gap of the semiconducting structures can be tuned within a range of 0.2864 eV to 1.17 eV substituting by different dopants. In addition, most of the doped structures maintain the low effective mass, 0.20〖 m〗_0 to 0.59m_0 for electron and 0.21〖 m〗_0 to 0.52m_0 for hole, which ensures the enhanced transport properties of GeSe based electronic devices. Moreover, when Ge is substituted with group V dopants, a magnetic moment is introduced and a spin-split is observed in the band structure in an otherwise non-magnetic GeSe monolayer. The real and imaginary part of the dielectric function can be substantially tuned in the low energy region with different dopants. The dopants also increase the static dielectric constant (3.5× maximum) of the monolayer. The optical absorption coefficient of the doped structures can be significantly improved (>2×) in the visible and infrared region. These intriguing results would encourage the applications of doped GeSe monolayer in next-generation electronic, optoelectronic and spintronic devices.