Fundamental mechanisms of hBN growth by MOVPE

TL;DR

This paper investigates the fundamental growth mechanisms of hexagonal boron nitride (hBN) by MOVPE, revealing how flow modulation epitaxy (FME) enables high-quality 2D layer growth by restoring boron chemisorption at sheet edges.

Contribution

It uncovers the core growth mechanisms of hBN by MOVPE and demonstrates how FME can activate 2D growth through periodic surface reconstruction changes.

Findings

Contradicts the belief that gas-phase reactions reduce growth efficiency.

Identifies two growth mechanisms based on ammonia flow and pressure.

Shows FME enables sustained 2D growth by restoring boron chemisorption.

Abstract

Hexagonal boron nitride is a promising material for many applications ranging from deep UV emission to an ideal substrate for other two dimensional crystals. Although efforts towards the growth of wafer-scale, high quality material strongly increased in recent years, the understanding of the actual growth mechanism still remains fragmentary and premature. Here, we unveil fundamental growth mechanisms by investigating the growth of hBN by metalorganic vapor phase epitaxy (MOVPE) in a wide range of growth conditions. The obtained results contradict the widespread opinion about the importance of parasitic gas-phase reactions decreasing the growth efficiency. Two different growth mechanisms that depend on ammonia flow and reactor pressure can be distinguished. Both mechanisms are effective in the case of polycrystalline growth, but the growth of highly ordered, flat layers, is strongly hindered. The problem is caused by a low efficiency of boron chemisorption on N-terminated edges of sp2-BN sheets forming the atomic steps on the surface of the layer. Two-dimensional growth can be activated and sustained by the flow modulation epitaxy (FME) method, an alternate switching of ammonia and TEB flows. The success of the FME method is explained in terms of periodic changes between N- and B-terminated reconstructions at the edges of sp2- BN sheets, which restore boron chemisorption. The presented results identify the fundamental growth mechanisms, which is the prerequisite for any further deterministic development of efficient, high-quality, large-scale hBN growth with MOVPE.