Direct Growth of Hexagonal Boron Nitride Thick Films on Dielectric Substrates by Ion Beam Assisted Deposition for Deep‐UV Photodetectors

Abstract High quality hexagonal boron nitride (h‐BN) thick films are indispensable for practical deep‐ultraviolet (DUV) photodetector applications. However, the controllable synthesis of h‐BN films in terms of thickness and crystallinity often requires high growth temperatures, tedious chemical precursors and, catalytic transition metal substrates, that will eventually hinder their applicability. In this work, the direct growth of h‐BN films with thickness of 50–500 nm on silicon(100), sapphire, and quartz substrates by ion beam assisted deposition at a lower temperature (≈500 °C) without employing extra catalysis is reported. The as‐synthesized h‐BN thick films are stoichiometric, smooth, and continuous without obvious pinholes and cracks, consisting of nanocrystalline domains on the dielectric substrates, distinct from those grown on metallic substrates. More intriguingly, the DUV photodetector fabricated from a 500 nm thick h‐BN film on quartz substrate exhibits high peak responsivity (0.5 A W⁻¹) with a ultrahigh on/off ratio of >10³ at 204 nm, a high rejection ratio (R_204nm/R_250nm > 10³), a large specific detectivity (6.92 × 10⁹ Jones), and a sharp cutoff wavelength at 218 nm. The work herein demonstrates the great potential of this form of h‐BN thick films toward the development of DUV photodetectors.