Mechanical peeling characteristics of large-scale high-crystallinity hBN films

Hexagonal boron nitride (hBN), a two-dimensional material with a bandgap of 5.9 eV, can be given priority for the dielectric substrate and mechanical release layer. The sapphire was used for the epitaxy growth of large-scale high-crystallinity hBN films, in which the sapphire exerted significant compressive stress onto the hBN layer with the thickness increases. The maximum thickness of high-crystallinity hBN on sapphire was determined to be 35 nm in our LPCVD system, and then the self-peeling phenomenon was observed with the further increase in thickness. Based on the thick high-crystallinity film and intriguing stress, the hBN film of 1 cm × 1 cm was stripped from the sapphire substrate by facile mechanical exfoliation. The hBN with various thicknesses was synthesized to study the effects on the epitaxy of AlN films. The AlN film grown on an 18 nm hBN/sapphire template exhibited optimum stress relief, grains lateral coalescence efficiency, and crystal-quality improvement. The transferred hBN/AlN heterostructure maintained structural integrity, high crystallinity, and heterojunction properties. In contrast to laser lift-off and chemical lift-off, the technology of hBN-assisted mechanical exfoliation and the transferable high-quality hBN/AlN heterojunction has great industrialization potential for ultraviolet photonics, high-power LEDs, and next-generation micro-LEDs.