Easy-peeling growth of triangular hBN flakes and their demonstration in vacuum ultraviolet photodetectors

An easy-peeling growth method for high-quality triangular hBN flakes was developed by adjusting the Fe–Ni–Cr solution composition and optimizing a specially designed cooling protocol. This method could induce the reprecipitation of BN powder between the grown hBN crystals and the metal ingot, forming an isolating layer that enabled the hBN crystals to be scraped off using a thin and hard medium while preserving their integrity. A 41 mm² area and 171 μm thick hBN flake was successfully peeled from the ingot. Both the narrow (002)-plane X-ray diffraction peak width of 0.079° and the Raman E_2g mode peak width of 7.7 cm⁻¹ indicate the high crystalline quality of the hBN flakes. Furthermore, a vacuum ultraviolet photodetector was fabricated using the peeled hBN flake, exhibiting a photo-to-dark current ratio exceeding three orders of magnitude and a photoresponse time of tens of milliseconds. The photodetector also demonstrated long-term operational stability under 185 nm irradiation for 30 minutes. The device performance further proved the superior crystalline quality of the hBN flakes obtained via the newly developed growth method.