Ultra-narrowband hot-electron photodetection with Friedrich-Wintgen bound states in the continuum
Efficient operations of hot-electron photodetectors (HE PDs) require strong energy deposition in metals assisted by device-dependent optical resonances whose spectral properties are fundamental to electrical performances, particularly in terms of 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. Therefore, we propose a design of HE PDs that exhibits ultra-narrowband photoelectric conversions through Friedrich-Wintgen bound states in the continuum (BIC). In our work, COMSOL is used for the analysis of opto-electronic coupling model, structural parameter optimization and material selection. Opto-electronic coupling reveals that the phase reversal of the guided mode resonance (GMR) enable the HE PD support dual Friedrich-Wintgen BICs through COMSOL simulation, which arise from the coupling between optical Tamm states (OTS) and guided mode resonance. The strong coupling and destructive interference of OTS and GMR result that the radiation losses of a mode are significantly reduced. Due to the phase reversal of GMR, dual FW BICs with significant field enhancement is achieved. We select suitable parameters for the structure by using COMSOL parameters sweeps. The study presents that the designed device exhibits high absorption efficiencies (>0.97) and enhanced responsivities (> 1 mA/W). The high Q-factor quasi-BICs enables near-unity and ultra-narrowband absorptions within the Au layer, allowing the efficiency of the hot electron transfer process to be significantly enhanced within an extremely small wavelength range 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.
