Strain‐Free GaSb Quantum Dots as Single‐Photon Sources in the Telecom S‐Band

Abstract

Generating single photons in the telecommunication wavelength range from semiconductor quantum dots (QDs) and interfacing them with spins of electrons or holes is of high interest in recent years, with research mainly focusing on indium‐based QDs. However, there is not much data on the optical and spin properties of gallium antimonide (GaSb) QDs, despite it being a physically rich system with an indirect to direct bandgap crossover in the telecom wavelength range. This work investigates the (quantum‐) optical properties of GaSb QDs, which are fabricated by filling droplet‐etched nanoholes in an aluminum gallium antimonide (AlGaSb) matrix. Photoluminescence (PL) features from isolated and highly symmetric QDs are observed that exhibit narrow linewidth in the telecom S‐band and show an excitonic fine structure splitting of up to µeV. Moreover, time‐resolved measurements of the decay characteristics of an exciton are performed and the second‐order photon autocorrelation function of the charge complex is measured to , revealing clear antibunching and thus proving the capability of this material platform to generate non‐classical light.

Unveiling the electronic structure of GaSb/AlGaSb quantum dots emitting in the third telecom window

“…The analysis of the TDPL data revealed the presence of a considerable energy barrier that suggests an inefficiency in the transfer of non-resonantly generated carriers into QD states. This idea is further supported by the recent findings reported on the temporal dynamics of this QD system, thus pointing towards the need for resonant excitation schemes for more efficient carrier transfer mechanisms [16]. Use of either coherent resonant excitation or incoherent quasi-resonant excitation should provide true single exciton lifetimes, with the former being the most efficient excitation-decay scheme and thus preferential for reaching optimal singleand entangled-photon metrics.…”

“…The presence of such an energy barrier agrees well with the time-resolved PL response of the GaSb QDs collected with above-bandgap excitation, which show a relatively slow radiative decay rate that is dominated by the trapping of carriers during their movement from QW to QDs. Additionally, the second-order autocorrelation function obtained from these QDs exhibits signatures of a carrier reservoir effect [16]. Therefore, from a practical application point of view, a more efficient way to inject carriers would be to excite them to the QDs resonantly either to the QD GS or QD ES transition which has been the preferable method for state-of-the-art single-and entangled-photon sources [5,49,50].…”

“…Strain-free GaSb/AlGaSb QDs grown by in-filling LDE-nanoholes have been recently proposed as deterministic sources of non-classical light emission at telecom wavelengths. These QDs exhibit narrow exciton lines resulting in single-photon emission in the telecom S-band with state-of-the-art homogeneity for a self-assembled growth process [14][15][16], making them an excellent candidate for quantum communication. From a device perspective, QD-based single-photon sources greatly benefit from employing resonant [12,17] or quasi-resonant [9,[18][19][20] excitation schemes which, however, require precise knowledge about the available energy states in the QDs.…”

Purcell‐Enhanced Single‐Photon Emission in the Telecom C‐Band

“…Unfortunately, this material platform is typically limited to wavelengths below 1300 nm, [ 12 ] with the exception of the exploitation of strain‐relaxing layers like metamorphic buffers. [ 13–15 ] Metamorphic buffers as well as InP‐based systems [ 16–19 ] have been used to reach wavelengths in the telecom C‐band, and recent works on the GaSb/AlGaSb system [ 20 ] highlight GaSb QDs as another candidate for single‐photon sources.…”