Optimization of Growth and Properties of Unintentionally Doped Single Crystalline Ga₂O₃ Using Pulsed Laser Deposition

Although pulsed laser deposition (PLD) is one of the most cost-effective techniques for growing epitaxial thin films, its use for obtaining single-crystal β-Ga₂O₃ is still challenging. In this work, we report on the systematic investigation of the effect of PLD growth conditions on the structural and optical properties of β-Ga₂O₃ thin films grown on different substrates, such as sapphire, Si, p-GaN and Ga₂O₃. X-ray diffraction (XRD) analyses show that the films grown on sapphire and p-GaN exhibit a single crystalline structure along the [-201] direction, while the films grown on Si substrate are polycrystalline in nature with [400] direction as the dominant peak. Increase in the substrate temperature and the number of laser pulses results in a considerable peak shift in 2θ-scans irrespective of the substrate used, indicating presence of strain in the film. The XRD rocking curves are investigated to evaluate the crystal quality with respect to the type of substrate and growth conditions. While Field Emission Scanning Electron Microscope (FESEM) images reveal variations in the morphology, High Resolution Transmission Electron Microscope (HRTEM) characterizations show different structural defects that affect the material quality, the extent of which is observed to depend on the growth conditions and the substrate type. Atomic force microscopy (AFM) analyses further reveal that the surface roughness changes as the temperature increases from 800⁰C to 850⁰C, as well as due to the increase in the number of laser pulses. For the optimized samples, optical characterizations show a typical Ga₂O₃ absorption curve, while a defect band emission is weak. However, the energy gap of the samples widens as the growth temperature and the number of laser pulses are increased. Raman spectroscopy analyses shows the effect of defects and strain on the material quality. Post-annealing under different conditions is carried out, and structural as well as optical characterizations reveal enhancement in the film properties. The results obtained in this study will assist in the optimization of β-Ga₂O₃ properties, which is essential for its use in optoelectronic and high-power device applications.