Deep ultraviolet emission in hexagonal boron nitride grown by high-temperature molecular beam epitaxy

Abstract

We investigate the opto-electronic properties of hexagonal boron nitride grown by high temperature plasma-assisted molecular beam epitaxy. We combine atomic force microscopy, spectroscopic ellipsometry, and photoluminescence spectroscopy in the deep ultraviolet to compare the quality of hexagonal boron nitride grown either on sapphire or highly oriented pyrolytic graphite. For both substrates, the emission spectra peak at 235 nm, indicating the high optical quality of hexagonal boron nitride grown by molecular beam epitaxy. The epilayers on highly oriented pyrolytic graphite demonstrate superior performance in the deep ultraviolet (down to 210 nm) compared to those on sapphire. These results reveal the potential of molecular beam epitaxy for the growth of hexagonal boron nitride on graphene, and more generally, for fabricating van der Waals heterostructures and devices by means of a scalable technology. LETTEROriginal content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.

High-temperature molecular beam epitaxy of hexagonal boron nitride layers

“…4,15 The high optical quality of our hBN grown at high temperatures on highly oriented pyrolytic graphite (HOPG) has been confirmed by both spectroscopic ellipsometry and photoluminescence spectroscopy. 33,37 Using AFM we also observe hexagonal moir e patterns, consistent with the close rotational alignment of the hBN lattice and the graphite substrate. 33,39 In this paper, we present our recent results on the hightemperature PA-MBE growth of hBN monolayers with atomically controlled thicknesses for 2D applications and on the growth of significantly thicker hBN layers for potential DUV applications.…”

“…We have already demonstrated that we can control the hBN layer coverage by adjusting the epitaxial growth temperatures for submonolayer thicknesses. 33,37 Several hBN layers were grown under the same B and active nitrogen fluxes on sapphire and HOPG substrates in the temperature range from 1390 to 1690 C. 37 At the highest growth temperatures, only a small density of hBN islands was observed and the coverage gradually increased to a complete hBN monolayer by decreasing the growth temperature. This effect has been explained by hBN sublimation at high MBE growth temperatures above 1390 C. 37 Another way to control reproducibly the hBN monolayer coverage is to change the MBE growth time.…”

“…40 In this study, we use thermocouple readings to measure the substrate temperature. 33,37,40 We have used a high-temperature Veeco effusion cell for sublimation of boron and a standard Veeco radio-frequency (RF) plasma source for active nitrogen. Boron has two naturally occurring stable isotopes, 11 B (80.1%) and 10 B (19.9%).…”

“…Following exfoliation, the HOPG substrates were further cleaned in toluene and annealed at 200 C in H 2 :Ar gas flow, as previously described. 33,37 The structural properties of the BN layers were studied in situ using reflection high-energy electron diffraction (RHEED) and after growth ex situ measurements were performed using x-ray diffraction (XRD).…”

“…[2][3][4][5][6][7] Recently, there have been many attempts to develop a reproducible technology for the growth of large area boron nitride layers by chemical vapor deposition, [19][20][21] metalorganic chemical vapor deposition 8,9,22 and molecular beam epitaxy (MBE). [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] Progress in MBE growth of boron nitride layers has been relatively slow, partly due to a lack of an efficient MBE source for boron, due to its very low vapor pressure.…”