Ultrawide bandgap semiconductors like β-Ga₂O₃ are promising candidates for power electronics and optoelectronics applications, thanks to their large bandgap energy (4.6-4.9 eV), high breakdown electric field (~8 MV/cm), broadband UV photodetection, and the availability of high-quality substrates. Beyond the thermodynamically stable β-Ga₂O₃, metastable polymorphs (α, γ, δ, κ) may offer additional functionalities, including piezoelectricity (κ-phase).

This thesis explores two different chemical approaches, one in vapor phase and one in aqueous solution to grow Ga₂O₃ films on c-plane sapphire substrates. This comparative approach provides insight into the strengths and limitations of each technique for controlled Ga₂O₃ synthesis.

The first approach is pulsed-liquid injection MOCVD (PLI-MOCVD), which, unlike conventional MOCVD systems, enables fine control over precursor delivery and dosing, improving chemical yield and reducing gallium waste, an important sustainability consideration. The resulting thin films show granular morphology with a low RMS roughness of ≈ 2nm, and an optical bandgap of ≈ 4.8 eV. Reducing the growth temperature and O₂ flow shifts the films from pure β-Ga₂O₃ to mixed β/κ-Ga₂O₃. Reducing the chamber pressure improves crystallinity, with a (-201) rocking-curve FWHM as low as 0.11°. Increasing the precursor concentration improves the growth rates, although introduces a minor fraction of misoriented grains. Finally, a photo-to-dark current ratio of ≈10³ under 250 nm illuminations highlights the potential of PLI-MOCVD β-Ga₂O₃ thin films for solar-blind detection.

The second approach is chemical bath deposition (CBD) followed by thermal annealing, which offers a low-cost, tunable pathway to crystalline Ga₂O₃, although the link between growth parameters and final properties remains poorly understood. The deposited structures are α-GaOOH microrods, obtained with a high deposited volume when using Ga(NO₃)₃ at a concentration of 0.050 M and NH₄OH as alkali to adjust the pH between 2.6 to 3.3. Two morphology transitions occur up to pH 4.6: from hierarchical to prismatic microrods, elongated along the b-axis, and then to bundles of high-aspect-ratio prismatic rods. Annealing in an O₂ environment successfully converts α-GaOOH to β-Ga₂O₃. Sintering begins at 1000 °C, and above this temperature the morphologies change into microplatelets with different characteristics. The presence of other Ga-related materials is observed in XRD and Raman Spectroscopy.

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