High-detectivity and -stability multilayer-graphene/Si-quantum-dot photodetectors with TiOx back-surface passivation layer

Abstract

We first report Si quantum dots (SQDs)-embedded SiO2 (SQDs:SiO2) multilayers (MLs)/Si photodetectors (PDs) using multilayer graphene (MLG) transparent conductive electrode (TCE) and TiOx back-surface passivation layer. With increasing number of graphene layer (Ln) to 5, the sheet resistance of the MLG TCE sharply decreases to ∼273 Ω/sq whilst the work function gradually increases to ∼4.71 eV, indicating p-type doping, useful for collection of photo-excited carriers at the MLG/SQDs:SiO2 MLs interface. At Ln = 4, the PD without TiOx exhibits best performance of 0.340 AW-1 responsivity (R) and 3.21 × 109 cm Hz1/2 W−1 specific detectivity (D*) at the peak wavelength. With TiOx on the back side of Si wafer (Ln = 4), the R slightly increases to 0.351 AW-1, but the D* is greatly enhanced to 9.42 × 1011 cm Hz1/2 W−1, resulting from the sharp reduction of the dark current by the suppression of the carrier recombination at the Si/TiOx interface. The PD performance is almost consistent for 1000 h in air, irrespective of the use of the TiOx layer. These behaviors are much better than ever achieved in graphene/Si wafer PDs.