Deterministic fabrication of circular Bragg gratings coupled to single quantum emitters via the combination of in-situ optical lithography and electron-beam lithography

In the present work, we investigate the coupling of deterministically pre-selected In(Ga)As/GaAs quantum dots (QDs) to low Q circular Bragg grating cavities by employing a combination of state-of-the-art low-temperature in-situ optical lithography and electron-beam lithography. The spatial overlap between the cavity mode and quantum emitter is ensured through the accurate determination of the QD position via precise interferometric position readout. Simultaneously, the high precision of the electron-beam lithography is exploited for the cavity fabrication. In order to optimize the spectral overlap, prior to cavity fabrication, finite-difference time-domain simulations are performed to estimate the spectral position of the cavity mode. A Purcell factor of 2 together with an increased count rate is reported for a deterministically positioned cavity where the emission line is detuned by 3.9 nm with respect to the cavity mode. This non-negligible Purcell enhancement for large detunings and, thus, the large range where this can be achieved points towards the possibility of using the cavity for the simultaneous enhancement of spectrally distinct transitions from the same quantum emitter located spatially in the mode maximum. Furthermore, investigations on the bending of the cavity membrane and the effects on the cavity mode and QD emission are presented.