Abstract
The linear optical response of the ultrawide bandgap h‐BN is investigated by spectroscopic ellipsometry. The ordinary dielectric function of h‐BN is determined up to 25 eV on a high‐quality single‐crystal platelet. The direct bandgap and the high‐energy transitions are characterized with the aid of ab initio self‐consistent GW calculations and the optical properties are calculated using the Bethe–Salpeter equation. The dispersion of the ordinary refractive index in the visible and UV part of the spectrum below the bandgap is in excellent agreement with previous transmission experiments. A sharp excitonic peak at 6.1 eV associated with the direct bandgap dominates the absorption spectrum, and a second peak is observed at 6.8 eV. At higher energies, a strong absorption peak emerges at 15 eV associated with higher σ → σ* transitions. As a consequence of the unique electronic band structure of h‐BN, a transparency window is observed in the far‐UV region between 7 and 13 eV, where the light penetration depth reaches a value of 38 nm, as opposed to the value of 0.8 nm at the absorption peak of the fundamental bandgap.
Highlights
Ultrahigh bandgap semiconductors are central to a wide range of a wide range of fields, such as waste treatment and water photolysis,[12,13,14] photopolymerization curing of nanocomposite coatings,[15] and high-resolution lithography.[16]
We present a spectroscopic ellipsometric study of high-quality single-crystal h-BN for energies up to 25 eV using synchrotron radiation
We have conducted a detailed ellipsometric study of h-BN over an extended energy range up to 25 eV using synchrotron radiation. This is the first ellipsometric study performed with synchrotron radiation in 2D/layered compounds
Summary
Ultrahigh bandgap semiconductors are central to a wide range of a wide range of fields, such as waste treatment and water photolysis,[12,13,14] photopolymerization curing of nanocomposite coatings,[15] and high-resolution lithography.[16]. Www.advancedsciencenews.com www.adpr-journal.com in high dislocation densities and a significant degradation of the internal quantum efficiency To circumvent these drawbacks, advancements in the design of deep-UV LEDs using AlN substrates with very low dislocation densities are currently being actively investigated.[20,21] On the other hand, direct wide bandgap oxides have aroused a notable interest for the realization of future UV applications.[22] In particular, considerable efforts are being devoted to develop Ga2O3-based devices.[23] because of the relatively low bandgap of the most stable β À Ga2O3 phase (reported in the 4.6–4.9 eV range),[22] this material is not a real contender for applications in the UVC region. This fact, together with the fact that h-BN exhibits an exceptionally good thermal conductivity and can be integrated in 2D devices, could be exploited in future far-UVC technological applications
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