Structural and optical characterization of electron Beam–Deposited Dy2O3 thin films on n-GaAs(111) substrate for photonic applications

Abstract

In this study, dysprosium oxide thin films with a thickness of 15 nm were deposited onto an n-type gallium arsenide (111) substrate using electron beam evaporation under ultra-high vacuum conditions. The deposition process, carried out at 250 °C and followed by thermal annealing at 400 °C, yielded uniformly smooth films with good structural quality and interfacial integrity. Structural analysis through scanning electron microscopy and X-ray diffraction revealed uniform triangular surface features and confirmed the cubic phase of dysprosium oxide, with crystallographic alignment to the gallium arsenide substrate. Fourier-transform infrared spectroscopy validated the formation of dysprosium–oxygen bonds. The optical properties were extracted using spectroscopic ellipsometry. The refractive index exhibited normal dispersion, and the optical band gap was determined to be 4.09 ± 0.03 eV. Wemple–DiDomenico modeling provided the oscillator energy (5.02 ± 0.05 eV) and dispersion energy (9.80 ± 0.07 eV), while dielectric function analysis identified sharp electronic transitions attributed to intra-4f states of trivalent dysprosium ions. In the infrared region, classical dispersion relations enabled the extraction of key parameters, including the high-frequency dielectric constant (3.28 ± 0.05), plasma frequency (1.81 ± 0.04) × 10¹⁴ Hz, carrier relaxation time (2.26 ± 0.03) × 10⁻¹⁵ s, and carrier concentration to effective mass ratio ((3.69 ± 0.08) × 10⁴⁷ g⁻¹ cm⁻³). Energy loss analysis through surface and volume energy loss functions revealed distinct plasmonic and interband excitation features. Optical conductivity measurements highlighted excitonic and bulk plasmon activity in the 2.7–3.8 eV range. Nonlinear optical behavior was evaluated using Miller's rule, yielding a linear susceptibility of 0.155 ± 0.004 esu, a third-order susceptibility of (9.74 ± 0.21) × 10⁻¹⁴ esu, and a nonlinear refractive index of (2.40 ± 0.06) × 10⁻¹² esu. Overall, the dysprosium oxide thin films demonstrated excellent crystallinity, high optical quality, and strong third-order nonlinear response, positioning them as promising candidates for advanced optoelectronic and photonic applications, including ultraviolet photodetectors, nonlinear optical modulators, and integrated optical devices.