Enhancement of efficiency and long-term stability in graphene/Si-quantum-dot heterojunction photodetectors by employing bis(trifluoromethanesulfonyl)-amide as a dopant for graphene

We for the first time employ bis(trifluoromethanesulfonyl)-amide as a dopant for graphene to enhance the efficiency and the stability of graphene/Si quantum dot (SQDs)-embedded SiO₂ (SQDs:SiO₂) multilayer (ML) heterojunction photodetectors (PDs). With increasing the doping concentration (n_D) to 30 mM, the sheet resistance of the doped-graphene transparent conductive electrode (TCE) sharply decreases to ∼155 ohm sq^-1 with only 1% reduction in its transmittance at 550 nm, whilst the work function gradually increases to ∼4.95 eV, indicating p-type doping, useful for the graphene/SQDs:SiO₂ MLs interface. The DC conductivity/optical conductivity ratio saturates to ∼75 at n_D = 20 mM, much larger than the minimum industry standard (= 35) for the optoelectronic applications of TCEs. The PDs optimized at n_D = 20 mM exhibit 0.413 A W^-1 responsivity (R), 92 dB linear dynamic range, 1.09 × 10¹⁰ cm Hz^1/2 W^-1 detectivity, and 81.33% external quantum efficiency at a peak wavelength of 630 nm, and the loss of R is almost negligible while the PDs are kept for 700 h in air. These characteristics are comparable to those of commercially-available Si PDs and better than those of previously-reported graphene/Si PDs.