Transferable single-crystal GaN thin films grown on chemical vapor-deposited hexagonal BN sheets

Abstract

Single-crystal gallium nitride (GaN) layers were directly grown on centimeter-scale hexagonal boron nitride (h-BN). Using chemical vapor deposition (CVD), centimeter-scale h-BN films were synthesized on a single-crystal Ni(111) and readily transferred onto amorphous fused silica supporting substrates that had no epitaxial relationship with GaN. For growing fully coalescent GaN layers on h-BN, the achievement of high-density crystal growths was a critical growth step because the sp2-bonded h-BN layers are known to be free of dangling bonds. Unlike GaN layers grown on a typical heterogeneous sapphire substrate, the morphological and microstructural results strongly suggest a high-density growth feature that is driven by the atomic cliffs inherent in the CVD-grown h-BN layers. More importantly, the GaN layers grown on CVD-grown h-BN exhibited a flat and continuous surface morphology with well-aligned crystal orientations both along the c-axis and in-plane, indicating the characteristics of GaN heteroepitaxy on h-BN. A method for depositing high-quality semiconductor thin films on a two-dimensional material has been developed by researchers in Korea. Growing one defect-free material on another is difficult because of their different atomic structures, particularly when very thin samples are required. Now, Gyu-Chul Yi and co-workers from Seoul National University in Korea have grown large areas of single crystals of the semiconductor gallium nitride directly on boron nitride, which is useful for flexible electronics. They used chemical vapor deposition, which works by exposing a hot volatile gas incorporating atoms of the top material to a cooler substrate. The gallium nitride films could be readily transferred to silica substrates. Since the technique can produce large areas of the material it is a promising for making flexible devices on a commercial scale. Here, we utilize large-size scalable single-crystal 2D films to grow single crystalline inorganic semiconductors. Centimeter-scale hexagonal boron nitride (h-BN) films were synthesized on a single-crystal Ni(111) using chemical vapor deposition (CVD). Single-crystal GaN layers were directly grown on h-BN using metal–organic vapor phase epitaxy. The CVD-grown h-BN exhibited many atomic cliffs that enabled us to grow high-density GaN islands to be merged as homogeneous and flat GaN films. We also investigated the crystallinity and growth mechanism of the GaN films grown on CVD-grown h-BN using transmission electron microscopy and X-ray diffraction.