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) [1]. 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 [2]. 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 [1()10] 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[0001] parallel to the Ni[111] 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 [1], 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 [0001]h-BN || [111]Ni, [112()0]h-BN || [1()10]Ni and [11()00]h-BN || [1() 1()2]Ni . The achievement of h-BN epitaxial growth by MBE allows us to clarify fundamental properties, such as near-band-gap luminescence.

[1] Y. Kobayashi et al., J. Crystal Growth 298 (2007) 325.
[2] 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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