Work

Influences of Zn flow rate and temperature on the defect state-related photoelectronic properties of MOCVD-grown ZnGa2O4

Year: 2025

Type: article

Abstract: Spinel-structural ZnGa 2 O 4 has attracted considerable attention for novel high-power device applications due to its broad transparent range, wide bandgap of ∼4.80 eV, and high breakdown voltage characteristics. Herein, we focus on the evolution of the optical, electronic, and structural properties of ZnGa 2 O 4 films under different Zn flow rates and temperature loading, as determined by spectroscopic ellipsometry, optical transmittance, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and first-principles calculations. Remarkably, non-classical temperature-dependent evolution of the crystal-related band gap E g and defect-related Urbach tail energy E U has been observed in an ultra-wide temperature range of 10–873 K using the two optical characterization techniques combined with a temperature-loading module. Specifically, the temperature dependency of E U only partially conforms to the Bose-Einstein distribution, due to the effects of oxygen-based defect emission. The results from XRD-based structural observation, PL-based sub-bandgap emission, and XPS-based atomic-ratio scanning also collectively demonstrate a strong correlation between E U and oxygen-based defect emission. The valence-band maxima and valence-band offset, as determined by ultraviolet photoelectron spectroscopy, further support the elucidation of the impacts of the different-level oxygen-based defect states caused by the Zn flow rate on the band structure of ZnGa 2 O 4 . These systematic consequences related to the defect stage are thus promising as a beneficial reference in the continual developments of ZnGa 2 O 4 -based optoelectronic, spintronic, electronic, sensing, optical, and related applications.

Source: Results in Engineering

DOI: 10.1016/j.rineng.2025.108511