A nano-hybrid plasmon-exciton material with an enhanced biexciton emission increases the efficiency of the photodetector at high excitation intensities

Abstract

Semiconductor quantum dots (QDs) have a wide absorption spectrum spreading from UV to the visible region and high photoluminescence (PL) quantum yield (QY) what determine possible use of their films for re-emitting coatings enhancing the photodetector spectral range. Unlike fluorescent organic dyes, the QDs absorption doesn’t saturate at high excitation intensities and can absorb more than one photon per particle due to the biexciton generation. However, due to the high rate of the Auger nonradiative relaxation, the QDs biexciton PL QY is much lower than the single-exciton one, what reduces the overall PL QY and the photodetector photosensitivity at the high excitation intensities. An employment of the Purcell effect in the plasmon nanocavities should increase the biexciton PL QY thus overcoming this limitation. To use this effect, we designed a thin-film plasmon–exciton material containing QDs and silver nanoplates (SNPs) in which the QDs’ PL band and the SNPs’ absorption band are overlapped. To demonstrate the advantage of the designed (QD-SNP)-film, we have compared effects of QD-film and (QD-SNP)-film on the photoresponse of the Si-based photodetector. The response of a photodetector to pulse excitation at 266 nm was negligible and increased after the deposition of the QD-film on its surface. However, at the high excitation intensities, the photosignal was reduced due to the biexcitons formation. The addition of SNPs increased the photoresponse at high excitation intensities. We attribute this improvement to a strong enhancement of QD biexciton PL in the QD-SNP material, which became predominate at high excitation intensities.