Tunable electronic properties of germanene and two-dimensional group-III phosphides heterobilayers

In this research work, the 2D structure of the germanene layer is compounded with 2D group-III phosphides: AlP and GaP. The planar structure of AlP and low-buckled GaP have been taken to form the bilayer patterns. In each case, three stacking patterns are considered, and their relaxed interlayer distance and binding energy have been reported. The binding energy being around in the range between ~150 to 210 meV shows the existence of weak van der Waals interactions between the layers. The heterostructures containing germanene and these two phosphides show an opening of a large indirect bandgap of magnitude range of ~200 meV to 600 meV, which can be tuned by changing interlayer distance and by incorporating bi-axial compressive and tensile strain. Although their normal bandgap, which significantly changes with SOC, is an indirect one, whilst tunning the interlayer distance band gap jumps from unsymmetrical point to symmetrical Dirac cones and becomes direct on K points. The charge carrier mostly concentrates on the p-orbitals of the germanene in the conduction regions; thus, the electrical properties of germanene will be retained, and the carrier will provide a much faster device response property. The absence of the phosphides influence makes them the intended substrate for growing the germanene layer on top of that. Again, due to the bandgap at Dirac cones being opened and jumps between the Dirac cones and band gap changes with SOC tropological insulator can be formed, and Quantum Spin Hall effect may exist.