Versatile van der Waals heterostructures of gamma-GeSe with h-BN/graphene/MoS2

The recent discovery of a novel hexagonal phase of GeSe (gamma-GeSe) has triggered great interest in nanoelectronics applications owing to the electrical conductivity of its bulk phase being even higher than that of graphite while its monolayer is a semiconductor. For potential applications, the construction of functional two-dimensional (2D) contacts is indispensable. Herein, via first-principles calculations, we propose the design of van der Waals heterostructures (vdWHs) of gamma-GeSe contacting graphene, 2D h-BN and MoS2 as representatives of metallic, insulator, and semiconductor partners, respectively. Our work shows that the h-BN or graphene layer donates electrons to the gamma-GeSe layer, resulting in n-doping in gamma-GeSe, while the MoS2 layer accepts electrons from the gamma-GeSe layer, leading to p-doping of the latter. The gamma-GeSe/BN heterostructure has a type-I band alignment with large band offsets, indicating that BN can be used as an effective passivating layer to protect gamma-GeSe from environmental disturbance while maintaining its major electronic and optical characteristics. The gamma-GeSe/graphene heterostructure is prone to having a very low Schottky barrier of tens of meV, easily overcome by thermal excitation, making it tunable by strain and external electric fields. The gamma-GeSe/MoS2 vdWH forms a Z-scheme interface, which is beneficial for carrier splitting and photon utilization. Our work indicates that gamma-GeSe can be well passivated by BN, and form an intimate contact with graphene for high charge injection efficiency and with MoS2 for efficient carrier splitting for redox reactions.