Two stage epitaxial growth of wafer-size multilayer h-BN by metal-organic vapor phase epitaxy – a homoepitaxial approach

Van der Waals heterostructures based on hexagonal boron nitride (h-BN) and other 2D materials may pave the way for future electronic applications. Wafer-scale uniform h-BN substrates are a must in this respect. In this work, we demonstrate a new growth regime which allows for scalable, uniform synthesis of high quality h-BN layers on 2' sapphire substrates. We propose a new approach to metal organic vapour phase epitaxy of h-BN layers on sapphire substrates. The growth scheme involves an intermediary BN buffer layer grown under self-limiting conditions (continuous flow) followed by the final growth of h-BN with flow modulated epitaxy in one growth run. This scheme can be regarded as homoepitaxial growth of h-BN on a self-limiting buffer. Our studies show that the buffer layer allows to control the nucleation at the crucial early stages of BN layer growth, suppressing unwanted out-of-plane growth. It can also be used to control the density of point-like defects responsible for unwanted luminescence from the h-BN layer. Moreover, our results show that the buffer effectively suppresses the creation of amorphous BN at the sapphire/h-BN interface.