Plasmon-coupled sub-bandgap photoluminescence enhancement in ultra-wide bandgap CuO through hot-hole transfer

Ultra-wide bandgap oxide semiconductors are garnering widespread interest for numerous applications, including high-power electronics, deep-UV opto-electronics, quantum devices, and applications in hostile environments. CuO has recently been shown to be a good contender for ultra-wide bandgap oxide materials. CuO's ultra-wide bandgap property is still in its infancy as far as scientific understanding is concerned. Herein, sub-bandgap emission properties of ultra-wide bandgap CuO thin films, deposited using a facile and low-thermal budget solution-process have been systematically investigated using temperature-dependent photoluminescence measurements. Interestingly, near-infrared (NIR) emission has been observed in ultra-wide bandgap CuO with sub-bandgap (488 nm) excitation suggesting involvement of defect and tail states in emission properties. Further, with the incorporation of Au nanoparticles, four-fold enhancement in the NIR emission was observed. Temperature dependent photoluminescence measurements have suggested enhanced Purcell effect in Au and CuO. The enhanced NIR emission can be assigned concertedly to metal-enhanced fluorescence, plasmon-coupling with photoluminescence and hot-carrier transfer from the metal. Time-resolved photoluminescence measurements have shown clear change in the emission dynamics with Au coating (decay time changed from 7.6 ns to 3 ns). Further, systematic DFT studies have been performed to clearly understand the effect of defects on the emission and absorption properties of ultra-wide bandgap CuO. Finally, the effect of Au on other optical and electrical features has been studied using electron paramagnetic resonance measurements and current-voltage characteristics. This study will expand the understanding of the optical and electrical properties of ultra-wide bandgap CuO for better performing optoelectronic devices.