Stabilization and Semiconductor Functionality of Metastable δ-Ga₂O₃: Buffer Layer Engineering for Deep UV Photodetection

The epitaxial growth and semiconductor functionality of δ-Ga 2 O 3 thin films were demonstrated using mist chemical vapor deposition. A high-quality δ-Ga 2 O 3 film was grown on YSZ(111) substrate utilizing a β-Fe 2 O 3 buffer layer on a bcc-ITO electrode. X-ray diffraction analysis revealed the formation of a single-phase δ-Ga 2 O 3 with a bixbyite structure, as evidenced by clear 222 diffraction peaks at 33.6°. The epitaxial relationships and sharp interfaces between layers were further validated by transmission electron microscopy, with selected area electron diffraction patterns definitively establishing the bixbyite crystal structure. Photoluminescence excitation spectroscopy revealed an absorption edge at 4.5 eV with a peak near 4.9 eV. We demonstrated the first semiconductor functionality of δ-Ga 2 O 3 through a vertical Schottky barrier photodiode structure. This structure exhibited photoresponsivity in the deep UV region, with a maximum value of 1.25 mA/W at approximately 5.1 eV. These results validate the presence of δ-Ga 2 O 3 while highlighting its potential in deep UV optoelectronics.