Growth of hexagonal BN crystals by traveling-solvent floating zone

TL;DR

This paper demonstrates a novel traveling-solvent floating zone method for growing large, high-quality hexagonal boron nitride crystals, which are crucial for advanced applications and research.

Contribution

It introduces a new crystal growth technique for h-BN using TSFZ, achieving high-quality crystals with optimized conditions and detailed characterization.

Findings

Successful growth of h-BN crystals with 3-5 mm diameter and 2-10 mm length.

High lattice quality confirmed by Raman spectroscopy and minimal defect signals.

Viability of TSFZ method for producing large, high-quality h-BN crystals.

Abstract

Large, high-purity single-crystals of hexagonal BN (h-BN) are essential for exploiting its many desirable and interesting properties. Here, we demonstrate via X-ray tomography, X-ray diffraction and scanning electron microscopy that h-BN crystals can be grown by traveling-solvent floating-zone (TSFZ). The diameters of grown boules range from 3 - 5 mm with lengths from 2 - 10 mm. Tomography indicates variable grain sizes within the boules, with the largest having areas of $\approx$ 1 mm $\times$ 2 mm and thickness $\approx$ 0.5 mm. Although the boules contain macroscale flux inclusions, the h-BN lattice itself is of high quality for samples grown under optimized conditions. The currently optimized growth procedure employs an Fe flux, moderate N$_2$ pressure ($P_{N2} \approx$ 6 bar), and a growth rate of 0.1 mm/h. Raman spectroscopy for an optimized sample gives an average linewidth of 7.7(2) cm$^{-1}$ for the E$_{\mathrm{2g}}$ intralayer mode at 1365.46(4) cm$^{-1}$ and 1.0(1) cm$^{-1}$ for the E$_{\mathrm{2g}}$ interlayer shear mode at 51.78(9) cm$^{-1}$. The corresponding photoluminescence spectrum shows sharp phonon-assisted free exciton peaks and minimal signal in the energy range corresponding to carbon-related defects ($E$ = 3.9 4.1 eV). Our work demonstrates the viability of growing h-BN by the TSFZ technique, thereby opening a new route towards larger, high-quality crystals and advancing the state of h-BN related research.