Growth Mechanism of Exfoliable GaN by van der Waals Epitaxy on Wrinkled Hexagonal Boron Nitride

The excellent physical and chemical properties of two-dimensional (2D) materials provide the possibility to promote the further development of 3D III-nitride semiconductors. Growing GaN films on 2D materials like hexagonal boron nitride (h-BN) can reduce the defects and stress caused by lattice mismatch and thermal mismatch and improve the crystal quality of GaN. Here, the growth mechanism of exfoliable GaN films grown on processed wrinkled h-BN/sapphire substrates by van der Waals epitaxy is reported. The processed wrinkled h-BN is obtained from natural wrinkled h-BN through O2 plasma treatment. The O2 plasma creates new atomic steps in the wrinkles and also additional defects in the flat areas. Metal-organic chemical vapor deposition was used to grow GaN, and it was found that GaN preferentially nucleated along the processed wrinkles. The physical mechanism of preferential nucleation of GaN along h-BN wrinkles was investigated with first-principles calculations, which reveals that compared with flat areas, the wrinkles showed greater N atom adsorption energy (-5.55 eV). The complete growth process of GaN nucleation along the wrinkles, followed by lateral growth of islands and finally merging to form a flat single-crystal GaN film, was fully demonstrated. The obtained GaN film has a typical atomic-step terrace, a dislocation density of 7.23 x 108 cm-2, and a low compressive stress of 0.095 GPa. Due to the weak van der Waals force between the h-BN layers, the obtained GaN film can be easily released. Our work provides a new strategy for the growth of high-quality exfoliable GaN films on 2D materials, laying the foundation for the preparation of transferable GaN flexible devices.