Anisotropic index of refraction and structural properties of hexagonal boron nitride epilayers probed by spectroscopic ellipsometry

Abstract

The anisotropic index of refraction of 200 μm thick boron-10 enriched hexagonal boron nitride (h-BN) freestanding epilayers grown by metalorganic chemical vapor deposition has been measured using spectroscopic ellipsometry in the UV (4.0–5.1 eV) spectral range. It was found that the index of refraction for the polarization mode with an electric field perpendicular to the c-axis (ordinary, no) is much higher than that with an electric field parallel to the c-axis (extraordinary, ne). By inclusion of turbostratic- (t-) phase layers within h-BN having an average inclination angle (θ) with respect to the ideal c-plane, a simple method for quantifying θ has been deduced. Our results revealed that the presence of t-phase layers decreases the optical anisotropy of h-BN and that a signature of improved crystalline quality is an increase in the ordinary index of refraction (no) as a result of the average incline angle θ approaching 0° and predicted that no = 2.7 and ne = 1.5 at 280 nm for single crystalline h-BN epilayers. More importantly, our results demonstrated that spectroscopic ellipsometry is an effective technique for characterizing the crystalline quality of h-BN epilayers with the advantages of being noninvasive and highly sensitive.

Ellipsometry Study of Hexagonal Boron Nitride Using Synchrotron Radiation: Transparency Window in the Far‐UVC

“…Spectroscopic ellipsometry measurements were also used to reveal the predominant or character of BN films prepared by magnetron sputtering. [ 49 ] Recently, the ellipsometric technique has been applied to characterize the crystalline quality of h ‐BN samples with the presence of turbostratic layers, [ 50 ] but a comprehensive ellipsometric study on h ‐BN giving insight into the optical properties is still lacking. Ellipsometry measurements allow the dielectric function of h ‐BN to be determined without the need of performing the Kramers–Kronig analysis that is necessary in the case of reflectance and absorption measurements.…”

Comparative Study of Boron Precursors for Chemical Vapor‐Phase Deposition‐Grown Hexagonal Boron Nitride Thin Films

“…The CVD‐grown h ‐BN easily incorporates turbostratic BN ( t ‐BN), which is a disordered phase of h ‐BN along the growth direction. [ 25 ] t ‐BN can be formed under undesirable growth conditions, which degrade device performance. We then clarified the crystal structures of BN by XRD.…”

“…Thus, wafer‐scale mass production is expected to be realized through hetero‐epitaxy of BN thin films grown on foreign substrates. There are several growth methods for growing BN films, such as thermal chemical vapor‐phase deposition (CVD), [ 4–27 ] plasma‐assisted CVD, [ 28–31 ] and molecular beam epitaxy (MBE). [ 32 ] BN films have been demonstrated on various substrates, including sapphire, [ 4–7,9–26 ] Cu, [ 8 ] Ni, [ 21,27,28 ] SiC, [ 24,26 ] GaN, [ 29 ] Si, [ 30,31,33 ] and highly‐oriented pyrolytic graphite.…”

“…There are several growth methods for growing BN films, such as thermal chemical vapor‐phase deposition (CVD), [ 4–27 ] plasma‐assisted CVD, [ 28–31 ] and molecular beam epitaxy (MBE). [ 32 ] BN films have been demonstrated on various substrates, including sapphire, [ 4–7,9–26 ] Cu, [ 8 ] Ni, [ 21,27,28 ] SiC, [ 24,26 ] GaN, [ 29 ] Si, [ 30,31,33 ] and highly‐oriented pyrolytic graphite. [ 32 ] The boron precursors include borazine (B 3 N 3 H 6 ), [ 8 ] boron halides (BF 3 , BCl 3 , and BBr 3 ), [ 9,27,28 ] triethyl boron ((C 2 H 5 ) 3 B, TEB), [ 4,5,10–23 ] trimethyl boron ((CH 3 ) 3 B, TMB), [ 24,25 ] and diborane (B 2 H 6 ).…”

Hexagonal boron nitride nanophotonics: a record-breaking material for the ultraviolet and visible spectral ranges

“…Besides, hBN is an essential building block for two-dimensional electronic and optoelectronic devices, 19 being widely used as a high-quality dielectric and encapsulation material. 20 Despite the wide use of hBN in nanophotonics and optoelectronics, only a few studies [21][22][23] have determined its anisotropic optical response and in the relatively narrow wavelength ranges of 245-310 nm, 21 220-780 nm, 22 and 1530 nm. 23 Furthermore, the optical properties were studied via transmittance spectroscopy and micro-reflectance, which have a limited accuracy, and the near-field microscopy, which yields a result at a single wavelength.…”