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Hexagonal boron nitride is a promising material for many applications rangingfrom deep UV emission to an ideal substrate for other two dimensional crystals.Although efforts towards the growth of wafer-scale, high quality materialstrongly increased in recent years, the understanding of the actual growthmechanism still remains fragmentary and premature. Here, we unveil fundamentalgrowth mechanisms by investigating the growth of hBN by metalorganic vaporphase epitaxy (MOVPE) in a wide range of growth conditions. The obtainedresults contradict the widespread opinion about the importance of parasiticgas-phase reactions decreasing the growth efficiency. Two different growthmechanisms that depend on ammonia flow and reactor pressure can bedistinguished. Both mechanisms are effective in the case of polycrystallinegrowth, but the growth of highly ordered, flat layers, is strongly hindered.The problem is caused by a low efficiency of boron chemisorption onN-terminated edges of sp2-BN sheets forming the atomic steps on the surface ofthe layer. Two-dimensional growth can be activated and sustained by the flowmodulation epitaxy (FME) method, an alternate switching of ammonia and TEBflows. The success of the FME method is explained in terms of periodic changesbetween N- and B-terminated reconstructions at the edges of sp2- BN sheets,which restore boron chemisorption. The presented results identify thefundamental growth mechanisms, which is the prerequisite for any furtherdeterministic development of efficient, high-quality, large-scale hBN growthwith MOVPE.

Fundamental mechanisms of hBN growth by MOVPE