Catalyst-free growth of two-dimensional hexagonal boron nitride few-layers on sapphire for deep ultraviolet photodetectors

Two-dimensional (2D) hexagonal boron nitride (h-BN) is a promising candidate as a supporting substrate, a gate dielectric and a protecting layer for 2D electronic and photonic devices. Transition metals were usually adopted as substrates for the synthesis of 2D h-BN, however, catalyst-free growth of high-quality h-BN on dielectric substrates is still very challenging. Herein, we report the catalyst-free growth of 2D h-BN few-layers on sapphire substrates by ion beam sputtering deposition (IBSD). We find that the h-BN grown under conventional conditions is nonstoichiometric with an excess of B element, resulting in a large number of N vacancy defects and poor crystalline quality. The wafer-scale high quality 2D h-BN layers were synthesized on sapphire by the combination of surface nitridation and N+ sputtering. Furthermore, the 2D h-BN few-layers on sapphire were used to fabricate deep ultraviolet photodetectors, which exhibit better performance in comparison with the devices fabricated by the transferred h-BN.