Strain Induced Bandgap Engineering in Wafer‐Scale Hexagonal Boron Nitride Thick Epitaxial Films for Broadband Solar‐Blind Ultraviolet Detection

ABSTRACT The Earth's atmosphere selectively intercepts ultraviolet (UV) light, endowing solar‐blind UV (Solar blind, 200–280 nm) detection with low interference and a low false alarm rate, which is irreplaceable in multiple fields. Hexagonal boron nitride ( h ‐BN), an ultra‐wide bandgap semiconductor, is an ideal solar blind detection material but is limited by a fixed intrinsic bandgap and poor thickness tunability. Herein, we achieved heteroepitaxial growth of 2‐inch h ‐BN films (several nm–2 µm) on sapphire via low‐temperature plasma‐enhanced chemical vapor deposition (PECVD). Thickness accumulation induces in‐plane compressive and out‐of‐plane tensile strains, narrowing the h ‐BN bandgap from 5.72 to 4.87 eV. Density functional theory (DFT) calculations confirm that the bandgap variation is dominated by the conduction band minimum (Γ point) shift, as it is highly sensitive to biaxial compressive and tensile strains, unlike the valence band maximum (M point). The fabricated metal‐semiconductor‐metal (MSM) photodetectors cover the range from 185 to 280 nm with pA‐level dark current, high responsivity, and excellent high‐temperature/long‐term stability. This work breaks through the traditional bottleneck in h ‐BN bandgap engineering via thickness‐mediated stress variation, providing a novel strategy and experimental foundation for the large‐scale fabrication of high‐performance full‐band solar blind photodetectors.