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We present a model dielectric function composed of critical point functions in order to parameterize the temperature and wavelength dependencies of the dielectric function of InAs. This model is based on Adachi’s critical point model, with simple wavelength-dependent analytical functions whose parameters change linearly with temperature. The calculated dielectric function at room temperature is in excellent agreement with previously published data. We apply this model in the spectral range of 0.7–5 eV and in the temperature range of room temperature to 250°C with in situ spectroscopic ellipsometry measurements on an InAs substrate. Spectroscopic measurements were performed continuously while slowly ramping sample temperature in a stepwise manner in the controlled ambient environment of an atomic layer deposition system. We find that our model matches excellently with all experimental data with deviations less than 2% in pseudoepsilon. Our model permits smooth interpolation of the dielectric function of InAs for any intermediate temperature in the range studied and therefore can be used to monitor temperature, for example, during thin film deposition processes by in situ spectroscopic ellipsometry. We propose that this model can be applied to other semiconductors as well as wider temperature ranges. 

We investigate the temperature-dependent complex dielectric function of bulk single-crystal In2O3 over the spectral range of 1–6 eV and temperatures from room temperature to 600 °C under high-vacuum conditions using in situ spectroscopic ellipsometry. The dielectric function was modeled using wavelength-by-wavelength and critical-point model dielectric function analyses. The dielectric function exhibits pronounced alterations with increasing temperature, attributed to thermally induced changes in the band structure and carrier dynamics. We identify direct and indirect interband transitions and excitonic contributions associated with the direct bandgap near the onset of absorption. At elevated temperatures, features in the dielectric function due to indirect transitions emerge below the direct bandgap energy, which shift toward shorter photon energies with increasing temperature. Combining our results with low-temperature data from previous reports, both observed shifts of the direct and indirect transitions can be seamlessly explained with the Bose–Einstein model. The direct transition is coupled less strong to the phonon bath (average temperature θB=512 K), leading to a smaller high-temperature slope (γ=−0.2 meV/K) than for the indirect transition (θB=360 K, γ=−1.3 meV/K). The exciton contributions diminish toward higher temperatures reflected by the decrease in amplitude and increase in broadening model parameters. Our parameter set can be used to calculate the model dielectric function In2O3 at elevated temperatures. 

A set of ultrawide bandgap single-crystal NdGaO3 samples cut with crystallographic surface orientations (001), (101), and (110) are investigated by using generalized spectroscopic ellipsometry. We report the complex anisotropic dielectric functions in the spectral range from 0.73 to 9.0 eV, for polarization along directions a, b, and c of the orthorhombic unit cell. A Kramers–Kronig consistent parameterized model was utilized to identify critical point structures and their association with band-to-band transitions, and the results from density functional theory (DFT) calculations for the electronic band structure of NdGaO3 are compared. A Cauchy parameter analysis for the three refractive indices is performed in the below bandgap spectral range. Dielectric functions along lattice directions a, b, and c and their respective bandgap energy values are very similar. Below the bandgap energy, the refractive index differences for directions a and b are very small (0.34% on average) while index differences with direction c (approximately 1.25%) lead to effective positive uniaxial optical properties (nc>na≈nb) toward the phonon modes spectral range. Our ellipsometry analysis determines the lowest band-to-band transitions of NdGaO3 to occur at Ea=6.46(6)eV, Eb=6.29(5)eV, and Ec=6.77(7)eV, i.e., Ec>Ea>Eb, while our DFT calculations predict the first transition to be lowest along the a axis. We discuss our findings in light of previous reports and present all parameters of our theoretical and experimental analyses. 

Electron paramagnetic resonance of Cr3+ ions in β-Ga2O3 is investigated using terahertz spectroscopic ellipsometry under magnetic field sweeping, a technique that enables the polarization resolving capabilities of ellipsometry for magnetic resonance measurements. We employed a single-crystal chromium-doped β-Ga2O3 sample, grown by the Czochralski method, and performed ellipsometry measurements at magnetic field strengths ranging from 2 to 8 T, at frequencies from 82 to 125 and 190 to 230 GHz, and at a temperature of 15 K. Analysis of the frequency-field diagrams derived from all Mueller matrix elements allowed us to differentiate between the effects of electron spin Zeeman splitting and zero-field splitting and to accurately determine the anisotropic Zeeman splitting g-tensor and the zero-field splitting parameters. Our results confirm that Cr3+ ions predominantly substitute into octahedral gallium sites. Line shape analysis of Mueller matrix element spectra using the Bloch–Brillouin model provides the spin volume concentration of Cr3+ sites, showing very good agreement with results from chemical analysis by inductively coupled plasma-optical emission spectroscopy and suggesting minimal occupation of sites with inactive electron paramagnetic resonance. This study enhances our understanding of the magnetic and electronic properties of chromium-doped β-Ga2O3 and demonstrates the effectiveness of high-frequency/high-field electron paramagnetic resonance generalized spectroscopic ellipsometry for characterizing defects in ultrawide-bandgap semiconductors. 

We describe a magnetic relation in analogy to the well-known dielectric Lyddane-Sachs-Teller relation [R. H. Lyddane , ]. This magnetic relation follows directly from the model equations for nuclear induction due to fast oscillating electromagnetic fields [F. Bloch, ] and relates the static permeability with the product over all ratios of antiresonance and resonance frequencies associated with all magnetic excitations within a given specimen. The magnetic relation differs significantly from its dielectric analog where the static properties are related to ratios of the squares of resonance frequencies. We demonstrate the validity of the magnetic Lyddane-Sachs-Teller relation using optical magnetization data from terahertz electron magnetic resonance spectroscopic ellipsometry measurements in the presence of an external magnetic field on an iron-doped semiconductor crystal of gallium nitride. 

The anisotropic optical absorption edge of β-Ga2O3 follows a modified Beer–Lambert law having two effective absorption coefficients. The absorption coefficient of linearly polarized light reduces to the least absorbing direction beyond a critical penetration depth, which itself depends on polarization and wavelength. To understand this behavior, a Stokes vector analysis is performed to track the polarization state as a function of depth. The weakening of the absorption coefficient is associated with a gradual shift of linear polarization to the least absorbing crystallographic direction in the plane, which is along the a-exciton within the (010) plane or along the b-exciton in the (001) plane. We show that strong linear dichroism near the optical absorption edge causes this shift in β-Ga2O3, which arises from the anisotropy and spectral splitting of the physical absorbers, i.e., excitons. The linear polarization shift is accompanied by a variation in the ellipticity due to the birefringence of β-Ga2O3. Analysis of the phase relationship between the incoming electric field to that at a certain depth reveals the phase speed as an effective refractive index, which varies along different crystallographic directions. The critical penetration depth is shown to be correlated with the depth at which the ellipticity is maximal. Thus, the anisotropic Beer–Lambert law arises from the interplay of both the dichroic and birefringent properties of β-Ga2O3. 

Abstract Efficient and compact single photon emission platforms operating at room temperature with ultrafast speed and high brightness will be fundamental components of the emerging quantum communications and computing fields. However, so far, it is very challenging to design practical deterministic single photon emitters based on nanoscale solid‐state materials that meet the fast emission rate and strong brightness demands. Here, a solution is provided to this longstanding problem by using metallic nanocavities integrated with hexagonal boron nitride (hBN) flakes with defects acting as nanoscale single photon emitters (SPEs) at room temperature. The presented hybrid nanophotonic structure creates a rapid speedup and large enhancement in single photon emission at room temperature. Hence, the nonclassical light emission performance is substantially improved compared to plain hBN flakes and hBN on gold‐layered structures without nanocavity. Extensive theoretical calculations are also performed to accurately model the new hybrid nanophotonic system and prove that the incorporation of plasmonic nanocavity is key to efficient SPE performance. The proposed quantum nanocavity single photon source is expected to be an element of paramount importance to the envisioned room‐temperature integrated quantum photonic networks.