Tuning the spontaneous emission of CdTe quantum dots with hybrid silicon–gold nanogaps

Abstract

Hybrid dielectric–metal nanogaps offer unique properties such as enhanced local density of optical states (LDOS) and simultaneously high quantum yield and coupling efficiency, with applications in bright single-photon sources, efficient nanoLEDs and imaging spectroscopy. In this work we report on silicon–gold hybrid nanogaps, considering both silicon nanorods on a gold film and gold nanorods on a silicon surface and compare them to their purely metallic and dielectric equivalent. To obtain the necessary nanometer-scale control, a combination of colloidal lithography, metal assisted chemical etching (MACE), and layer-by-layer polyelectrolyte approach were used to construct the nanogaps. Quantum emitters were incorporated in the nanogap in the form of a CdTe quantum dot monolayer. The efficient coupling between the quantum dot monolayer and the nanogap modes results in hybrid nanogaps outperforming their homogeneous counterpart, with the gold nanorod–silicon hybrid nanogap offering the largest emission rate enhancement factor of 51. Specifically, Purcell enhancements were increased by a factor of ∼2 for silicon nanorod–gold film and ∼1.5 for gold nanorod–silicon surface nanogaps compared to purely dielectric and metallic geometries respectively. These results, supported by FDTD simulations, highlight hybrid nanogaps as cornerstones for probing light–matter-interactions under extreme optical confinement with applications such as low cost and low power consumption ultrafast LEDs for short distance on-chip and chip-to-chip communications.