Direct-write projection lithography of quantum dot micropillar single photon sources

Abstract

We have developed a process to mass-produce quantum dot micropillar cavities using direct-write lithography. This technique allows us to achieve mass patterning of high-aspect ratio pillars with vertical, smooth sidewalls maintaining a high quality factor for diameters below 2.0 μm. Encapsulating the cavities in a thin layer of oxide (Ta2O5) prevents oxidation in the atmosphere, preserving the optical properties of the cavity over months of ambient exposure. We confirm that single dots in the cavities can be deterministically excited to create high-purity indistinguishable single photons with interference visibility (0.941 ± 0.008).

Quantum dot micropillar cavities with SiO2 hard mask microlenses

“…Building on the fabrication method developed in previous work 19 , microlenses were produced by leaving a layer of SiO2 hard mask on top of our devices. These could be used to tune the outgoing emission's numerical aperture and mode field diameter to better mode-match with an output single-mode fiber, with the thickness and cross-sectional profiles of the lens being key variables in accomplishing this.…”

“…The pillar structures studied here consist of 7(26) upper (lower) DBR pairs and are designed to emit photons around a wavelength of 940 nm. To fabricate our samples, we developed a novel direct-write photolithography method, allowing the mass-etching of high-aspect ratio pillars in GaAs and Al0.95Ga0.05As 19 (an SEM image of the devices formed is shown in Fig. 1a).…”