Bandgap energy of graphite-like hexagonal boron nitride

doi:10.1016/S0022-3697(01)00030-0

Journal of Physics and Chemistry of Solids

Volume 62, Issue 7, July 2001, Pages 1331-1334

https://doi.org/10.1016/S0022-3697(01)00030-0 Get rights and content

Abstract

We have carried out laser-induced fluorescence measurements of hBN powder at room temperature under different environmental conditions (dry powder and suspensions in water or ethanol). From fluorescence excitation spectra, the absorption onset, related to the bandgap energy of this indirect gap semiconductor, has been precisely determined to be E_g=4.02±0.01 eV. This result is of importance in view of large discrepancies in previously published data.

Introduction

Graphite-like hexagonal boron nitride (hBN) is one of important inorganic materials, which provides a basis for many advanced technologies. hBN is a good electrical insulator and an excellent thermal conductor widely used as material of crucibles for crystal growth and cells for molecular beam epitaxy. It has a low thermal expansion and high thermal and chemical stability in oxygen-free environments in addition to being transparent to X-rays. Materials for electronics and nuclear energy, lubricants and refractories are an incomplete list of applications of hBN.

Despite of the fact that hBN is the best studied polymorph of boron nitride, up to date no agreement concerning its band gap energy has been obtained. The analysis of the available literature data (Table 1) shows that the measured values of the hBN band gap energy (E_g) are widely dispersed in the range between 3.6 and 7.1 eV. It is, therefore, evident that the band gap energy of hBN cannot be regarded as been determined.

In the present work we have measured the band-gap energy of hBN powder by using laser-induced fluorescence (LIF) technique. This approach is very useful as it allows observing a very small material absorbance close to the absorption threshold and obtaining accurate values of the band-gap energy. The measurements have been done at room temperature under different environmental conditions: dry powder and powders suspended in water and ethanol.

Section snippets

Experimental

The experiments have been carried out using the pulsed ns MOPO laser (Spectra Physics) tunable over 0.2—1.8 μm spectral range. Suspensions in liquids and dry samples were excited (vertically, from the top site) in a cylindrical windowless stainless steel cell equipped by two optical fibers. The air-sample interface was situated above and very close to the horizontally positioned optical axis of the fibers. The use of this cell allows one to avoid the contamination of the measured spectra by

Results and discussion

The fluorescence spectra of dry hBN powder normalized on I_L are shown in Fig. 1. Three different fluorescence bands have been observed. (i) At excitation below 260 nm the fluorescence band is of the asymmetric shape with a maximum at 374 nm (UV1). It sharply grows in intensity at 363 nm and extends to the visible over 100 nm. (ii) At excitation between 260 and 310 nm a new structured UV2 band appears with two maxima situated at 336 and 354 nm and a shoulder at ∼320 nm. The UV1 band does almost not

Acknowledgements

V.L.S. and A.G.L. are grateful to the University Paris-Nord for financial support.

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¹: Permanent address: Kharkov State Politechnical University, 21 Frunze st., Kharkov 61002, Ukraine.

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Bandgap energy of graphite-like hexagonal boron nitride

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Acknowledgements

Mater. Res. Bull.

Fizika Tverdogo Tela (Sov. J. Solid State Phys.)

Fizika Tverdogo Tela (Sov. J. Solid State Phys.)

J. Electrochem. Soc.

J. Phys. Chem.