Cadmium defect-induced modulation of hole self-trapping in monoclinic gallium oxide for optoelectronic applications

Abstract

Self-trap holes (STHs) in β-Ga2O₃ prohibit p-type conduction in this material, severely limiting the homojunction-based optoelectronic applications. Here, we report that the presence of cadmium (Cd) impurity in β-Ga₂O₃ (CdGa₂O₃) drastically quenches STHs and significantly increases p-type conductivity in this material, making it promising for optoelectronics. Photoluminescence experiments show that Cd-induced defects in β-Ga₂O₃ significantly suppress the characteristic ultraviolet luminescence, indicating the reduction of STHs. The CdGa₂O₃ film shows the distinct recombination channels of green and blue emissions attributed to CdGa and VGa defects, which exhibit slow decay time constants of 38.45 and 13.31µs, respectively. Density functional calculations reveal that a few atom% of Cd in β-Ga₂O₃ induces an intermediate valence band state due to the formation of Cd_Ga and V_Ga defects in the octahedral sites. The calculated energy levels of Cd_Ga and V_Ga defects are 0.72 and 0.18 eV, respectively, which are significantly lower than the energy levels of 0.99 eV for STHs, resulting in the destabilization of STHs and promoting p-type conductivity. The Mott-Schottky measurement confirms the p-type conductivity in CdGa₂O₃ film with an acceptor concentration of 3.65×10¹⁷ cm^-3. This p-type CdGa₂O₃ film is used in fabricating Ag/p-CdGa₂O₃ Schottky diodes, which operate as high-performance self-powered ultraviolet photodetectors possessing a high responsivity of 164 mA/W and specific detectivity of 7.5×10¹¹Jones. This p-type CdGa₂O₃ film could provide better flexibility in designing efficient homojunction-based optoelectronic devices.