First-principles study of band alignment in passivated and doped GaN/WSe2 van der Waals heterojunctions.

van der Waals (vdW) heterojunctions formed between GaN and transition metal dichalcogenides (TMDs) hold promise for application in broadband photodetection. Here, we investigate the electronic structure of GaN/WSe2 heterojunctions. Ga-terminated GaN surfaces exhibit strong covalent interactions with WSe2, and the interfacial charge significantly perturbs the heterojunction band structure, thereby preventing effective modulation of the band alignment via GaN conductivity. In contrast, passivated GaN surfaces (pseudo-hydrogen) form robust vdW heterojunctions with WSe2, and their band alignment can be tuned from type-II to type-I through controlled GaN doping. This is consistent with the results we previously tested in our experiments. Our calculations provide good design guidance for van der Waals heterojunctions between GaN and 2D materials.