Molecular Beam Epitaxial Growth of Hexagonal Boron Nitride on Ni(111) Substrate
Chiun-Lung Tsai, Yasuyuki Kobayashi, and Tetsuya Akasaka
Materials Science Laboratory
Hexagonal boron nitride (h-BN), with its wide bandgap in the deep ultraviolet region, has been gaining interest since it was proposed as a promising material for optoelectronic applications. The h-BN epitaxial growth has been achieved using the metalorganic vapor phase epitaxy (MOVPE) . Parasitic reactions between sources in BN epitaxy by MOVPE can be avoided in molecular beam epitaxy (MBE) growth of h-BN. However, a polycrystalline BN structure was obtained by MBE and no successful MBE-grown h-BN epitaxy has been reported yet.
Here, we report the epitaxial h-BN growth on Ni(111) substrate by MBE . Elemental boron evaporated by an electron-beam gun and active nitrogen generated by a radio-frequency (RF) plasma source were used as the group-III and -V sources, respectively. Figure 1 shows in-situ reflection high energy electron diffraction (RHEED) pattern taken along the [
110] azimuth of Ni(111) surface at the end of 1000 Å BN growth. The unreconstructed intense streaky (1×1) patterns were seen immediately upon initiation of the MBE growth of BN, and the consistent streaky (1×1) pattern was recorded during the entire process till the end of 1000 Å BN growth. The streaky patterns observed throughout the entire growth carried out at a relatively low temperature of 890ºC not only indicate the formation of single-crystalline BN, but also mean the growth proceeded with a smooth growth front.
A representative XRD for the 1000 Å h-BN epitaxial film is shown in Fig. 2. Diffraction peaks from both the h-BN(0002) and h-BN(0004) planes along with the underlying Ni(111) substrate prove the formation h-BN with the orientation of h-BN parallel to the Ni direction. The inset of Fig. 2 shows the x-ray rocking curve of the h-BN epitaxial film characterized by the full width at half maximum (FWHM) of 0.61º. This FWHM from a 1000 A film is narrower than the best value ever reported , and can possibly be further decreased by optimizing the growth conditions and/or increasing the epitaxial film thickness. From the RHEED observation and XRD, the alignments between the h-BN film and the Ni substrate are h-BN || Ni, [11
20]h-BN || [ 110]Ni and [1 100]h-BN || [ 1 12]Ni . The achievement of h-BN epitaxial growth by MBE allows us to clarify fundamental properties, such as near-band-gap luminescence.
 Y. Kobayashi et al., J. Crystal Growth 298 (2007) 325.
 C.L. Tsai et al., J. Crystal Growth (in press).
Fig. 1. The RHEED pattern at the end of 1000 Å BN growth.
Fig. 2. The 2θ/ω XRD of the h-BN epitaxial film with an inset displaying the XRC.
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