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Aluminum gallium nitride (AlGaN) and the native oxide of GaN [gallium oxide (Ga2O3)] have become potential candidates for GaN-based high power metal-oxide-semiconductor devices. This paper discusses and analyzes the development of AlGaN/GaN and Ga2O3/GaN heterojunctions. Two techniques were followed for the formation of the epitaxial layers on silicon (Si) and sapphire (Al2O3) substrates: magnetron sputtering deposition for AlGaN and dry thermal oxidation for Ga2O3. The AlGaN layer was sputtered for two hours in a low pressure environment at room temperature using a combination of argon and nitrogen gases during deposition. The Ga2O3 was produced by dry thermal oxidation of the GaN-based samples. The samples were subjected to a two hour thermal treatment from 800°C to 1000°C. Characterization of the samples was conducted by X-ray Photoelectron Spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and atomic force microscopy (AFM). XPS analysis shows the presence of AlGaN and Ga2O3 compounds in the Ga-3D scan. EDX analysis confirms the results obtained through XPS. The film thickness was characterized by SEM studies and shown to be 34nm for AlGaN and 200nm for Ga2O3 after a two hour heat treatment at 900°C. AFM analysis confirms the results obtained through the SEM study.