To fabricate efficient devices, we need to make sure that a quantum dot is coupled to a single mode of the electromagnetic field.
We can approach such ideal situation by controlling the quantum dot spontaneous emission, through cavity quantum electrodynamics.
To do so, the quantum dot must be in both spectral and spatial resonance with the cavity mode. Yet, quantum dots usually grow with random spatial positions and a wide distribution of their spectral properties. As a result, usual nanofabrication techniques present fabrication yields in the low 10-4.
We have invented a technique which enables to fabricate as many as desired ideally coupled quantum dot-cavity devices, with a fabrication yield close to unity.
Our technique relies on a low temperature photolithography, with an in situ monitoring of the quantum dot emission.
The emission monitoring makes it possible to select the quantum dot with desired optical properties, to measure the quantum dot spatial location with 50 nm accuracy and to expose the photoresist to define a disk centered on the QD. The hole in the resist will later be used as a mask for the micropillar etching, ensuring that the quantum dot will be located at the maximum of the fundamental optical mode.
Dozens of micropillar microcavities with diameters ranging from 1 to 2.3 µm are fabricated. Each of them embeds a spectrally resonant quantum dot in its center. Using this technique, we have demonstrated on demand control the spontaneous emission for one or two QDs coupled to a cavity mode, with an acceleration of spontaneous emission close to 10. Increasing the quality factor of the cavity mode, we have recently demonstrated scalable implementation of strongly coupled QD cavity devices.
Further reading
“Controlled Light-Matter Coupling for a Single Quantum Dot Embedded in a Pillar Microcavity Using Far-Field Optical Lithography”, A. Dousse, L. Lanco, J. Suffczynski, E. Semenova, A. Miard, A. Lemaître, I. Sagnes, C. Roblin, J. Bloch, P. Senellart, Phys. Rev. Lett. 101, 267404 (2008)
“Scalable implementation of strongly coupled cavity-quantum dot devices” , A. Dousse, J. Suffczynski, R. Braive, A. Miard, A. Lemaître, I. Sagnes, L. Lanco, J. Bloch, P. Voisin, P. Senellart, Appl. Phys. Lett. 94, 121102 (2009)