Infrared dielectric functions and optical phonons of wurtzite Y_xAl_1−xN (0  ⩽  x  ⩽  0.22)

Abstract

YAlN is a new member of the group-III nitride family with potential for applications in next generation piezoelectric and light emitting devices. In this work we report the infrared dielectric functions and optical phonons of wurtzite (0001) YxAl1-xN epitaxial films with 0 ≤ x ≤ 0.22.The films are grown by magnetron sputtering epitaxy on c-plane Al2O3 and their phonon properties are investigated using infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The infrared-active E1(TO) and LO, and the Raman active E2 phonons are found to exhibit one-mode behaviour, which is discussed in the framework of the MREI model. The compositional dependencies of the E1(TO), E2 and LO phonon frequencies, the high-frequency limit of the dielectric constant, ∞ , the static dielectric constant, 0 , and the Born effective charge ZB are established and discussed.

Metal‐Organic Chemical Vapor Deposition of Aluminum Yttrium Nitride

“…In Figure 6d, the determined bandgap values are plotted versus the Y content determined by TOF-SIMS. The experimental values of the sputtered samples presented by Sedrine et al [40] are shown as well as the theoretical values of Ramírez-Montez et al, [30] who calculated the direct and indirect wurtzite and cubic bandgaps of AlYN over the whole composition range, concluding that both the binary rock salt compounds as well as wurtzite Al 0.25 Y 0.75 N and YN have an indirect bandgap. These calculations underestimate the experimental bandgap of wurtzite AlN by 0.815 eV.…”

“…Different kinds of measurements were performed, such as phase analysis (2θ/θ-scan), azimuthal Φ-scan (e.g., to easily distinguish the presence of cubic inclusions), and pole figures (e.g., to estimate the presence of textures or twisting). While the AlYN layers deposited between 900 and 1000 °C showed typical wurtzite phase-related peaks (0002 peak at %35°-36°) and the cubic phase could not be detected, the layer grown at 1100 °C seemed to have traces of cubic phase inclusions, while the sample growth at 1200 °C was rich in cubic phase inclusions (100 peak at %31°-32°), [22,40] as visible in the Φ-scan (Figure 1).…”

“…[30] Nevertheless, compressive strain and the choice of a proper substrate with an off-cut or with a proper nucleation layer, and the choice of the right growth temperature can help to stabilize the desired wurtzite structure, as done for other metastable semiconductor materials, such as SiC. [36][37][38][39] The growth of AlYN has been demonstrated only by two groups so far: Linköping University [29,40] and TU Wien. [22,41] In both cases, the sputtering technique was used to grow the samples at temperatures below 1000 °C, and the maximum concentration of Y in crystalline wurtzite AlYN layers was below 22% and 15%, respectively.…”

Influence of the free-electron concentration on the optical properties of zincblende GaN up to 1×1020cm−3

“…Additionally, Raman measurements were performed to support the IRSE measurements. For quantitative comparison of the DFs and Raman spectra, we calculate the imaginary part of the dielectric loss function (ω) from pbp-DFs [74]: In the range ω < 1000 cm −1 , the Raman spectra are dominated by phonons from the substrates, namely the TO( ) Si at 521 cm −1 , the TO( ) 3C−SiC at 795 cm −1 , and the LO( ) Si at 972 cm −1 [75]. The TO( ) c−GaN phonon mode is forbidden and therefore not visible in these Raman spectra [76,77].…”

Modelling of Optical Damage in Nanorippled ZnO Produced by Ion Irradiation

“…For the samples studied here, the optical axes of ZnO are oriented parallel to the surface normal. Therefore, no mode conversion of p-polarized light to s-polarized light and vice versa occurs and standard ellipsometry can be applied [18,34]. The SE spectra of all samples were analysed by using a 3-layer physical model consisting of a bulk ZnO substrate, a ZnO damaged layer and a surface roughness layer, as illustrated in Figure 5.…”