Investigation of anisotropic mechanical, electronic, and charge carrier transport properties of germanium-pnictogen monolayers

Recently, novel two-dimensional (2D) GeP and GeAs systems have been fabricated by mechanical exfoliation and utilized in various applications. These developments have brought the 2D germanium-pnictogens, C2/m-GeX (X = N, P, As, Sb, and Bi) structures into the limelight. In this study, we systematically investigate the structural, mechanical, electronic, and charge carrier transport properties of GeX monolayers by using first-principles methods. Our results show that the considered systems are dynamically stable and possess anisotropic physical properties. Examined structures are found to be flexible, and their mechanical strength and stiffness decrease down the group-V, in line with the trends of the bond strength, cohesive energy, charge transfer, and electron localization function. Additionally, the zigzag in-plane direction is mechanically superior to the armchair direction. The electronic band structure calculations based on HSE06 hybrid functional with the inclusion of spin-orbit coupling indicate that GeX monolayers are either direct or quasi-direct semiconductors with band gaps lying within the infrared and visible spectrum. The estimated charge carrier mobilities are highly anisotropic and also differ significantly depending on the structure and carrier type. These unique properties render GeX monolayers as suitable 2D materials for flexible nanoelectronic applications.