The combination of
semiconductor quantum dots with photonic cavities
is a promising way to realize nonclassical light sources with state-of-the-art
performances regarding brightness, indistinguishability, and repetition
rate. Here we demonstrate the coupling of InGaAs/GaAs QDs emitting
in the telecom O-band to a circular Bragg grating cavity. We demonstrate
a broadband geometric extraction efficiency enhancement by investigating
two emission lines under above-band excitation, inside and detuned
from the cavity mode, respectively. In the first case, a Purcell enhancement
of 4 is attained. For the latter case, an end-to-end brightness of
1.4% with a brightness at the first lens of 23% is achieved. Using
p-shell pumping, a combination of high count rate with pure single-photon
emission (g(2)(0) = 0.01 in saturation) is achieved. Finally,
a good single-photon purity (g(2)(0) = 0.13) together with
a high detector count rate of 191 kcps is demonstrated for a temperature
of up to 77 K.
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.
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