Thickness-Dependent Phase Stability and Electronic Properties of GaN Nanosheets and MoS2/GaN van der Waals Heterostructures

The formation of GaN-based heterostructures is essential for optoelectronic applications, but it is greatly limited by the traditional heteroepitaxial method due to the impact of lattice mismatch. Integrating two-dimensional layered semiconductors (e.g., MoS2) on GaN surface into van der Waals (vdW) heterostructures can effectively overcome the constraint of lattice mismatch but also create the possibility to induce novel electronic and optical properties due to size and interface effects. Here we report the thickness effect on the structural, electronic, and optical properties of GaN nanosheets and MoS2/GaN van der Waals heterostructures based on hybrid density functional theory calculations. Our results demonstrate the thickness-driven structural transitions of GaN nanosheets from the wurtzite, to the haeckelite, to the graphitic phase, which is accompanied by a direct to-indirect band gap transition. The integration of a MoS2 monolayer on GaN nanosheets into MoS2/GaN vdW heterostructures exhibits the strong thickness dependence of the band gap, band alignment, and optical absorption coefficient. Overall, two-dimensional MoS2/GaN vdW heterostructures possess moderate band gaps (1.35-1.7 eV), type II band alignment, and large visible-light absorption coefficients, which make them potential candidates for photovoltaic and photocatalytic applications.