Cumulative effect of spectral downshifting, anti-reflection and space-charge region formation in enhancing the spectral response of self-powered silicon photodetectors on sensitisation with CdZnS/ZnS core-shell quantum dots

Abstract

Despite their ubiquity, Silicon (Si)-based photodetectors face intrinsic limitations that inhibit their performance, especially in the critical ultraviolet (UV) range. Downshifting of high energy photons by employing luminescent quantum dots (QDs) has up to now been the commonest photon harvesting technique in Si photodetectors. This research article describes the monolithic integration of CdZnS/ZnS core-shell QDs with Si photodetectors to make use of the spectral downshifting effect. Silicon detectors sensitised with these QDs have shown remarkably enhanced responsivity and external quantum efficiency over a broad spectral range of 300 - 1100 nm. Apart from the spectral down-shifting process, the anti-reflection effect of the QD film and the formation of a space charge region at the Si-CdZnS/ZnS interface have also contributed to enhanced device performance. The additive effect of spectral downshifting, anti-reflection effects and heterojunction formation has given these QD-sensitized devices enhanced responsivity and EQE values of 345 mA/W and 0.5, markedly higher than the values of 110 mA/W and 0.15 seen in pristine devices. Given the notable enhancement demonstrated without the need for the application of epitaxial techniques, this study may assist in mitigating the inherent limitations of Si photodetectors.