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This research investigates the electronic band structure and dielectric functions of NdGaO3.

April 8, 2026Journal of Applied Physics0 citationsOpen Access

Electronic band structure, band-to-band transitions, and anisotropic dielectric functions of orthorhombic NdGaO3

YTYousra TraouliUniversity of Nebraska–Lincoln UKUfuk Kilic RKRafał Korlacki

Key Points

This research investigates the electronic band structure and dielectric functions of NdGaO3.
Utilized generalized spectroscopic ellipsometry to analyze NdGaO3 samples.
Examined complex anisotropic dielectric functions across various crystallographic directions.
Applied a Kramers–Kronig consistent model for identifying band-to-band transitions.
Conducted density functional theory (DFT) calculations for comparison of electronic structures.
Identified lowest band-to-band transitions at 6.46 eV, 6.29 eV, and 6.77 eV along directions a, b, and c respectively.
Found minimal differences in refractive indices along a and b (0.34% on average) compared to c (1.25%).
Observed effective positive uniaxial optical properties with nc > na ≈ nb in the phonon modes spectral range.

Abstract

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 (ncna≈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., EcEaEb, 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.

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