Effect of the Growth Interruption on the Surface Morphology and Crystalline Quality of MOCVD-Grown h-BN

Abstract

Hexagonal boron nitride (h-BN) is one promising material class for applications in DUV optoelectronics due to the layered structure and ultra-wide bandgap. The synthesis of h-BN with smooth surface morphology and high quality on dielectric substrates is the key to construct efficient functional devices thereon. In this study, we reported wafer-scale h-BN on c-plane sapphire substrates by metal organic chemical vapor deposition utilizing the flow modulation epitaxy (FME) with growth interruptions. The effect of the growth interruption location within FME on the surface morphology and crystalline quality of h-BN films was systematically investigated. The interruption after the TEB injection could promote the mobility of B adatoms, and the interruption after the NH3 injection could further relieve the passivation of N terminal growth fronts and mitigate the parasitic gas-phase reaction between growth precursors. By simultaneously employing interruptions after TEB and NH3 injections, the growth rate of h-BN increased significantly from 0.16 nm/min to 4.76 nm/min, and the surface roughness of 2-nm-thick h-BN was reduced to 0.587 nm. In addition, h-BN grown with an interruption solely after the NH3 injection presented the best crystallinity because the relatively slow growth rate reduced the possibility of impurity incorporation.

Morphology Evolution of a h-BN Film Grown by Halide Vapor Phase Epitaxy at Different Growth Temperatures

“…To expedite this transition, it is essential to further increase the migration rate of B atoms and reduce parasitic reactions between B and N sources. Therefore, next, we will try to utilize a growth interruption method or flow modulation epitaxy, , where B and N sources are alternately introduced into the reactor. This will further enhance adatom surface migration and reduce parasitic gas-phase reactions, potentially allowing for the growth of larger-sized h-BN single-crystal thick films.…”

High-Crystallinity and High-Temperature Stability of the Hexagonal Boron Nitride Film Grown on Sapphire

“…The redshifted absorption peak originated from defects-assisted donor−acceptor pair transitions, such as nitrogen vacancies (V N ) and carbon impurities substitution defects in hBN film. 44 The 250 nm peak disappeared in samples-II and sample-III, thereby illustrating the peaks related to nitrogen-vacancy defects (V N ) in sample-I. The inset of Figure 2a shows the Tauc plot of samples, and the band gaps are determined by linearly extrapolating the leading edge.…”

“…The UV–visible absorption spectra were used to unravel the bandgap differences of the hBN film with direct bandgap property, as shown in Figure a, which shows a strong absorption for all three samples in the deep-ultraviolet spectral region below 220 nm due to an interband transition absorption, while weak absorption at 250 nm was also detected for sample-I. The red-shifted absorption peak originated from defects-assisted donor–acceptor pair transitions, such as nitrogen vacancies (V N ) and carbon impurities substitution defects in hBN film . The 250 nm peak disappeared in samples-II and sample-III, thereby illustrating the peaks related to nitrogen-vacancy defects (V N ) in sample-I.…”

Influence of sapphire substrate with miscut angles on hexagonal boron nitride films grown by halide vapor phase epitaxy

“…In a B-rich environment, the mobility of B atoms is small, causing h-BN to grow faster vertically than laterally. 49 Therefore, even though the h-BN nuclei develop into islands to some extent, the lateral extension is insufficient to form a continuous film. It is necessary to modulate growth conditions further to encourage the lateral growth of h-BN nuclei, allowing for the transition from 3D growth to 2D growth, thus getting the single-crystal h-BN thick films with a smooth surface.…”