Structure-Property Relationships of 2D Ga/In Chalcogenides

Abstract

Two-dimensional MX (M = Ga, In; X = S, Se, Te) homo- and heterostructures are of interest in electronics and optoelectronics. Structural, electronic and optical properties of bulk and layered MX and GaX/InX heterostructures have been investigated comprehensively using density functional theory (DFT) calculations. Based on the quantum theory of atoms in molecules, topological analyses of bond degree (BD), bond length (BL) and bond angle (BA) have been detailed for interpreting interatomic interactions, hence the structure–property relationship. The X–X BD correlates linearly with the ratio of local potential and kinetic energy, and decreases as X goes from S to Te. For van der Waals (vdW) homo- and heterostructures of GaX and InX, a cubic relationship between microscopic interatomic interaction and macroscopic electromagnetic behavior has been established firstly relating to weighted absolute BD summation and static dielectric constant. A decisive role of vdW interaction in layer-dependent properties has been identified. The GaX/InX heterostructures have bandgaps in the range 0.23–1.49 eV, absorption coefficients over 10−5 cm−1 and maximum conversion efficiency over 27%. Under strain, discordant BD evolutions are responsible for the exclusively distributed electrons and holes in sublayers of GaX/InX. Meanwhile, the interlayer BA adjustment with lattice mismatch explains the constraint-free lattice of the vdW heterostructure.

Structure–Property Relationships in Transition Metal Dichalcogenide Bilayers under Biaxial Strains

“…According to Gatti [ 59 ], an atomic expectation value results from the sum of bond contributions. As we did in previous works [ 28 , 61 ], a relationship was searched for between the bond degrees summation and the relative permittivity under zero frequency ε 1 (0) along the zz -direction. As two types of bonds coexist in the structures, namely M-X and X-X, the summation can be written as h|BD| M-X +k|BD| X-X , with h and k the parameters to be fitted.…”