Amorphous Gallium Oxide Nanosheets with Broad Absorption and Spin Polarization for Si‐Based UV‒Vis‒NIR Photodetectors

Abstract Achieving broad light absorption and high carrier separation efficiency is crucial for wide‐bandgap semiconductors to enable broadband photodetection applications. Here, amorphous gallium oxide nanosheets feature with broad absorption and spin polarization Wis synthesized, and assembled with graphene and p‐Si, realizing UV‒vis‒NIR photodetection. Extended X‐ray absorption fine structure reveals that a‐GaO_x NSs possess lower tetrahedral Ga occupation (10%) compared to crystalline β‐Ga₂O₃ (50%). UV‒vis‒NIR diffuse reflectance spectra and magnetic hysteresis loops demonstrate broad absorption and weak ferromagnetism of a‐GaO_x NSs, respectively. Density functional theory calculation further reveals sub‐gap states and spin polarization in a‐GaO_x NSs. Moreover, combined with Mott–Schottky curves, photoluminescence and time‐resolved photoluminescence spectra inferred the effective suppression of carrier recombination via spin polarization of a‐GaO_x NSs. The graphene/a‐GaO_x NSs/p‐Si photodetector incorporates a back‐to‐back rectifying junction, acquiring a dark current as low as 63 pA. All photogenerated carriers are in the depletion region of the photodetector favouring efficient charge separation. This photodetector exhibits a response time of τ_rise<60 ms and τ_fall<120 ms, and high specific detectivity 10¹³ Jones over 254–1064 nm light.