Structural and Electronic Properties of β-(Al_xGa_1–x)₂O₃ Active Layers for Space-Qualified Solar-Blind Photodetectors

This paper presents a detailed investigation of the structural, optical, and electronic properties of (Al x Ga 1– x ) 2 O 3 thin films used as active layers in solar-blind ultraviolet C (UVC) photodetectors onboard the INSPIRE-Sat 7 nanosatellite. Engineered via alloying Ga 2 O 3 with Al 2 O 3, these deep UV detectors exhibit a Gaussian spectral response centered at 215 nm with a full width at half maximum of 40 nm, enabling selective monitoring of solar irradiance in the Herzberg continuum (200–242 nm). The (Al x Ga 1– x ) 2 O 3 films are grown on c-plane sapphire substrates using pulsed laser deposition. Structural and optical analysis reveals that the engineered film exhibits the monoclinic β phase with a dominant (−201) orientation and the Al fraction of 0.58, inducing a 0.93 eV bandgap widening from 4.89 eV (Ga 2 O 3 ) to 5.82 eV. Complementary photoemission and X-ray absorption spectroscopy studies reveal a 0.17 eV valence band downshift and a 0.74 eV conduction band uplift due to the alloying at x = 0.58. Cathodoluminescence spectroscopy identifies broad emission peaks at 3.55, 3.34, and 3.10 eV, attributed to self-trapped hole states localized at O sites adjacent to Al and Ga, respectively, and donor–acceptor pair recombination, consistent with the band structure modifications induced by Al 2 O 3 alloying. These findings provide critical insights into β-(Al 0.58 Ga 0.42 ) 2 O 3 photodetector performance for Herzberg continuum detection in space applications.