Ultra-narrowband hot-electron photodetection with Friedrich-Wintgen bound states in the continuum

Efficient operations of hot-electron photodetectors (HE PDs) require strong energy depositions in metals assisted by device-dependent optical resonances whose spectral properties are fundamental to electrical performances, particularly with the linewidths of responsivity spectra. However, ultra-narrowband HE PDs based on thin, planar structures remain scarce due to the difficulty of achieving sufficiently narrow resonance linewidths. Here, we propose a design of HE PDs that exhibits ultra-narrowband photoelectric conversions through Friedrich-Wintgen bound states in the continuum (BIC). Optical studies based on modal analysis reveal that the phase reversal of the guided mode resonance enable the HE PD support dual Friedrich-Wintgen BICs, arising from the coupling between optical Tamm states and guided mode resonance. Probability-based electrical calculations show that, when suitable structural parameters are chosen for quasi-BIC excitations, the designed device exhibits high absorption efficiencies (> 0.97) and enhanced responsivities (> 1 mA/W), together with ultra-narrowband responsivity spectra with extremely small linewidths (∼ 1 nm). Furthermore, the analysis on external and internal quantum efficiencies indicates that the role of BIC excitations is primarily associated with optical responses. The proposed BIC-assisted HE PDs are expected to open the pathway for highly selective photoelectric conversion.