Controlling exciton spontaneous emission of quantum dots by Au nanoparticles

Abstract

As an ideal single-photon source, quantum dots (QDs) can play a unique role in the field of quantum information. Controlling QD exciton spontaneous emission can be achieved by anti-phase coupling between QD exciton dipole field and Au dipole field after QD film has been transferred onto the Si substrate covered by Au nanoparticles. In experiment, the studied InAs/GaAs QDs are grown by molecular beam epitaxy (MBE) on a (001) semi-insulation substrate. The films containing QDs with different GaAs thickness values are separated from the GaAs substrate by etching away the AlAs sacrificial layer and transferring the QD film to the silicon wafer covered by Au nanoparticles with a diameter of 50 nm. The distance <i>D</i> (thickness of GaAs) from the surface of the Au nanoparticles to the QD layer is 10, 15, 19, 25, and 35 nm, separately. A 640-nm pulsed semiconductor laser with a 40-ps pulse length is used to excite the QD samples for measuring QD exciton photoluminescence and time-resolved photoluminescence spectra at 5 K. It is found that when the distance <i>D</i> is 15–35 nm the spontaneous emission rate of exciton is suppressed. And when <i>D</i> is close to 19 nm, the QD spontaneous emission rate decreases to <inline-formula><tex-math id="M2">\begin{document}$ ~{10}^{-3} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20211863_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20211863_M2.png"/></alternatives></inline-formula>, which is consistent with the theoretical calculations. The physical mechanism of long-lived exciton luminescence observed in experiment lies in the fact that Au nanoparticles scatter the light field of the exciton radiation in the QD wetting layer, and the phase of the scattered field is opposite to the phase of the exciton radiation field. Therefore, the destructive interference between the exciton radiation field and scattering field of Au nanoparticles results in long-lived exciton emission observed in experiment.