Enhanced emission of charged-exciton polaritons from colloidal quantum dots on a SiN/SiO2 slab waveguide.

Xingsheng Xu,Xingyun Li

doi:10.1038/srep09760

Xingsheng Xu, Xingyun Li

Open Access

https://doi.org/10.1038/srep09760

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Abstract

We investigate the photoluminescence (PL) spectra and the time-resolved PL decay process from colloidal quantum dots on SiN/SiO2 wet etched via BOE (HF:NH4F:H2O). The spectrum displays multi-peak shapes that vary with irradiation time. The evolution of the spectral peaks with irradiation time and collection angle demonstrates that the strong coupling of the charged-exciton emission to the leaky modes of the SiN/SiO2 slab waveguide predominantly produces short-wavelength spectral peaks, resulting in multi-peak spectra. We conclude that BOE etching enhances the charged-exciton emission efficiency and its contribution to the total emission compared with the unetched case. BOE etching smoothes the electron confinement potential, thus decreasing the Auger recombination rate. Therefore, the charged-exciton emission efficiency is high, and the charged-exciton-polariton emission can be further enhanced through strong coupling to the leaky mode of the slab waveguide.

Highlights

We investigate the photoluminescence (PL) spectra and the time-resolved PL decay process from colloidal quantum dots on silicon nitride (SiN)/SiO2 wet etched via BOE (HF:NH4F:H2O)
As the irradiation time increased to 100 s, the total PL intensity increased slightly because of photo-oxidation[21], and the centre wavelength shifted to 583.7 nm (Fig. S1a)
Insert is a graphical description of exciton, bi-exciton and tri-exciton, where X represents exciton, BX bi-exciton, and TX represents tri-exciton; C1, C2, and C3 represent the radiative rates of exciton, bi-exciton and tri-exciton emissions. (d) Log-scaled lifetimes of emission of colloidal quantum dots (CQDs) on unetched SiN/SiO2 and that on BOE-etched SiN/SiO2

Summary

Introduction

We investigate the photoluminescence (PL) spectra and the time-resolved PL decay process from colloidal quantum dots on SiN/SiO2 wet etched via BOE (HF:NH4F:H2O). The evolution of the spectral peaks with irradiation time and collection angle demonstrates that the strong coupling of the charged-exciton emission to the leaky modes of the SiN/SiO2 slab waveguide predominantly produces short-wavelength spectral peaks, resulting in multi-peak spectra. Colloidal CdSe/CdS CQDs were synthesized, and it was found that the negatively charged exciton PL quantum yield reached 100% at low temperatures, where the Auger recombination was completely suppressed[8]. An exciton polariton can be regarded as a quasi particle with mixed properties of light and matter[17] This state has important applications in fields involving light matter interactions, such as in Bose-Einstein condensation (BEC)[18], low-threshold coherent emission[19], and low-threshold all-optical switches[17,20]. Waveguide exciton-polariton emission from colloidal quantum dots has been rarely reported

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Conclusion