Dielectric function of zinc-blende AlN from 1 to 20 eV: Band gap and van Hove singularities

Abstract

The dielectric function (DF) of phase-pure cubic AlN films is determined by ellipsometry. The sharp onset of the imaginary part of the DF defines the direct absorption edge corresponding to a conduction-to-valence band spacing at the center of the Brillouin zone (BZ) of 5.93 eV. Phonon-assisted transitions lead to the pronounced absorption tail below this edge from which the indirect gap of zinc-blende AlN is estimated with 5.3 eV. Transitions due to four additional critical points of the BZ are resolved at higher photon energies. The high-frequency and static dielectric constants are determined with 4.25 and 8.07, respectively.

Photoelastic properties of zinc-blende AlxGa1−xN in the UV: Picosecond ultrasonic studies

“…We associate the peak position in the wavelength dependence of n with the onset for optical electron-hole transition and correspondingly with the band gap E g of the alloy (i.e., E g = E 0 ). As was shown in previous studies with c-GaN [24], c-AlN [25], and (AlGa)N alloys [8] this is a good approximation and the values of E g defined in such a way are presented in Table I. We do not see any experimental evidence of indirect band gap in (AlGa)N which could happen when x approaches the value of 0.7 [8].…”

“…The values of E g measured in [8] are much closer to our data. We note that there is also a difference for c-AlN measured in [6,7] and more recent works on c-AlN [25] and (AlGa)N alloys [8]. The differences of our ellipsometry data with values obtained in earlier works [6,7] could possibly be related to different quality of the grown material, the accuracy of defining x, different substrates, and the models used in the ellipsometric analysis.…”

Optical and Electronic Properties of AlN, GaN and InN: An Analysis

“…The sharp onset above 7.20 eV is correlated with a critical point around the X-point of the BZ and above 7.95 eV is due to transitions along the [11 l]-direction. Other two transitions at 11.14 eV and 12.52 eV are assigned to L-andT-points of BZ [38], For comparison, ab-initio density functional theory [39] calculated results give a slightly larger band gap (6.18 eV). Instead of a main peak at 7.20 eV, a wide peak in the range of 7 to 10 eV is observed with a maximum at 8.04 eV.…”

“…Modified MDF seems to be closer to the experimental results than LDA first-principle calculations. For Zincblende A1N films, we take Roppischer's data [38] as an example. The sample was grown by RF plasma-assisted MBE on free 3C-SiC(001) substrates and the dielectric functions were recorded by a commercial ellipsometer.…”

Optical Properties

“…For instance, the In the inset of (a) the k-point density is increased by about one order of magnitude, while only quasielectronquasihole pairs with energies <10 eV and a broadening parameter of η = 0.1 eV are taken into account. Experimental spectra for zb-AlN [36] and wz-AlN [37] (black solid lines) are given for comparison. From [35] simplification of the QP treatment, e.g.…”