A journey of growth: β-Ga2O3 on GaN and sapphire via Pulsed Laser Deposition

Sammanfattning

The exceptional breakdown field and ultra-wide bandgap of beta-gallium oxide (β-Ga2O3) position it as a promising material for next-generation high-power electronics. This thesis systematically investigates the growth behaviour, structural quality, and surface morphology of β-Ga2O3 thin films deposited via Pulsed Laser Deposition (PLD) on both c-plane sapphire (Al2O3) and MOCVD-grown GaN-on-sapphire templates under identical conditions. Deposition parameters were mapped across a broad experimental matrix, varying substrate temperatures from 500°C to 800°C and oxygen background pressures from 10^-6 mbar (vacuum) to 10^-1 mbar. Characterization was performed using spectroscopic ellipsometry, X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Three main parameters were used to assess the overall quality of the films: growth rate, crystal quality, and surface roughness. First, the growth rate evolution is evaluated for all grown layers to delineate the material tendencies with respect to the growth conditions. Next, a comparative structural analysis of the (-201) crystal orientation is presented for both substrates to isolate how growth parameters influence overall crystalline quality. To overcome severe interfacial degradation caused by premature GaN substrate oxidation under oxygen-rich environments, a two-step deposition process utilizing an inert Argon (Ar) sacrificial buffer layer is introduced. Finally, the surface topography is analyzed to establish a correlation between substrate temperature and surface roughness (RMS). Together, these structured analyses provide a comprehensive framework for understanding β-Ga2O3 thin films deposited via PLD.