Al₂O₃ layers with thicknesses in the 25–120 nm range were deposited by plasma enhanced atomic layer deposition at 70 °C. Trimethylaluminum was used as organometallic precursor, O₂ and H₂O as oxidant agents and Ar as a purge gas. The deposition cycle consisted of 50 ms TMA pulse/10 s purge time/6 s of plasma oxidation at 200 W/10 s purge time. The optical constants and thicknesses of the grown layers were determined by spectroscopic ellipsometry, while the roughness was measured by atomic force microscopy, giving RMS values in the 0.29–0.32 nm range for films deposited under different conditions and having different thicknesses. High transmittance, ~90%, was measured by UV–Vis spectroscopy. X-ray photoelectron spectroscopy revealed that, with both types of oxidants, the obtained films are close to stoichiometric composition and, with high purity, no carbon was detected. Electrical characterization showed good insulating properties of both types of films, though the H₂O oxidant leads to better I-V characteristics.

β‐Ga₂O₃ thin films were grown on c‐plane sapphire substrates by plasma‐assisted molecular beam epitaxy. The films were grown using an elemental gallium source and oxygen supplied by an RF plasma source. Reflection high‐energy electron diffraction (RHEED) was used to monitor the surface quality in real time. Both in situ RHEED and ex situ X‐ray diffraction confirmed the formation of single crystal β‐phase films with excellent crystallinity on c‐plane sapphire. Spectroscopic ellipsometry was used to determine the film thicknesses, giving values in the 11.6–18.8 nm range and the refractive index dispersion curves. UV‐Vis transmittance measurements revealed that strong absorption of β‐Ga₂O₃ starts at ∼270 nm. Top metal contacts were deposited by thermal evaporation for I‐V characterization, which has been carried out in dark, as well as under visible and UV light illumination. The optical and electrical measurements showed that the grown thin films of β‐Ga₂O₃ are excellent candidates for deep‐ultraviolet detection and sensing.