David Quandt

Electrically driven single photon source based on a site-controlled quantum dot with self-aligned current injection

Electrical operation of single photon emitting devices employing site-controlled quantum dot (QD) growth is demonstrated. An oxide aperture acting as a buried stressor structure is forcing site-controlled QD growth, leading to both QD self-alignment with respect to the current path in vertical injection pin-diodes and narrow, jitter-free emission lines. Emissions from a neutral exciton, a neutral bi-exciton, and a charged exciton are unambiguously identified. Polarization-dependent measurements yield an exciton fine-structure splitting of (84 ± 2) μeV at photon energies of 1.28–1.29 eV. Single-photon emission is proven by Hanbury Brown and Twiss experiments yielding an anti-bunching value of g(2)(0) = 0.05 under direct current injection.

Fabrication and room temperature operation of semiconductor nano-ring lasers using a general applicable membrane transfer method

Semiconductor nanolasers are potentially important for many applications. Their design and fabrication are still in the early stage of research and face many challenges. In this paper, we demonstrate a generally applicable membrane transfer method to release and transfer a strain-balanced InGaAs quantum-well nanomembrane of 260 nm in thickness onto various substrates with a high yield. As an initial device demonstration, nano-ring lasers of 1.5 μm in outer diameter and 500 nm in radial thickness are fabricated on MgF2 substrates. Room temperature single mode operation is achieved under optical pumping with a cavity volume of only 0.43λ03 (λ0 in vacuum). Our nano-membrane based approach represents an advantageous alternative to other design and fabrication approaches and could lead to integration of nanolasers on silicon substrates or with metallic cavity.

Triggered high-purity telecom-wavelength single-photon generation from p-shell-driven InGaAs/GaAs quantum dot

We report on the experimental demonstration of triggered single-photon emission at the telecom O-band from In(Ga)As/GaAs quantum dots (QDs) grown by metal-organic vapor-phase epitaxy. Micro-photoluminescence excitation experiments allowed us to identify the p-shell excitonic states in agreement with high excitation photoluminescence on the ensemble of QDs. Hereby we drive an O-band-emitting GaAs-based QD into the p-shell states to get a triggered single photon source of high purity. Applying pulsed p-shell resonant excitation results in strong suppression of multiphoton events evidenced by the as measured value of the second-order correlation function at zero delay of 0.03 (and ~0.005 after background correction).

Semiconductor quantum dot to fiber coupling system for 1.3 um range

We present an alignment procedure which allows for precise gluing of a structure with an optically pumped quantum emitter to the end face of zirconia ferrule with a specially fabricated high numerical aperture single-mode fiber. The proposed method is an important step towards building a single-photon source based on an InGaAs quantum dot emitting in 1.3 μm range and located deterministically in a microlens fabricated by in-situ electron beam lithography and plasma etching to improve the photon extraction efficiency. Since single QDs are very dim at room temperature which hinders QD-fiber adjustment by maximizing the collected photoluminescence signal, the developed method uses light back-reflected from the top surface of the sample with microlens as a feedback signal. Using this approach, we were able to position the high-NA fiber over the center of the microlens with an accuracy of about 150 nm in a lateral direction and 50 nm in a vertical direction. The alignment accuracy was confirmed by following the room temperature emission from quantum wells embedded in a reference microlens. We also present initial low temperature tests of the coupling system mounted in a compact and portable Stirling cryocooler.

Enhanced photon-extraction efficiency from InGaAs/GaAs quantum dots in deterministic photonic structures at 1.3 μm fabricated by in-situ electron-beam lithography

The main challenge in the development of non-classical light sources remains their brightness that limits the data transmission and processing rates as well as the realization of practical devices operating in the telecommunication range. To overcome this issue, we propose to utilize universal and flexible in-situ electron-beam lithography and hereby, we demonstrate a successful technology transfer to telecom wavelengths. As an example, we fabricate and characterize especially designed photonic structures with strain-engineered single InGaAs/GaAs quantum dots that are deterministically integrated into disc-shaped mesas. Utilizing this approach, an extraction efficiency into free-space (within a numerical aperture of 0.4) of (10±2) % has been experimentally obtained in the 1.3 μm wavelength range in agreement with finite-element method calculations. High-purity single-photon emission with g(2)(0)<0.01 from such deterministic structure has been demonstrated under quasi-resonant excitation.The main challenge in the development of non-classical light sources remains their brightness that limits the data transmission and processing rates as well as the realization of practical devices operating in the telecommunication range. To overcome this issue, we propose to utilize universal and flexible in-situ electron-beam lithography and hereby, we demonstrate a successful technology transfer to telecom wavelengths. As an example, we fabricate and characterize especially designed photonic structures with strain-engineered single InGaAs/GaAs quantum dots that are deterministically integrated into disc-shaped mesas. Utilizing this approach, an extraction efficiency into free-space (within a numerical aperture of 0.4) of (10±2) % has been experimentally obtained in the 1.3 μm wavelength range in agreement with finite-element method calculations. High-purity single-photon emission with g(2)(0)<0.01 from such deterministic structure has been demonstrated under quasi-resonant excitation.

Atomic structure and electronic states of InAs(Sb)/GaAs submonolayer quantum dots

Summary form only given. Submonolayer-grown semiconductor nanostructures are promising for high power and high speed laser devices. They are formed by a cycled deposition of the active material with a thickness well below the critical thickness for Stranski-Krastanov transition and well below one monolayer (ML), alternating with several ML thick matrix material. They were successfully implemented in high speed (>25 Gbit/s) vertical-cavity surface emitting lasers operating up to 120°C. In this contribution, the structural changes upon additional supply of Sb are studied on the atomic scale using XSTM. The InAsSb agglomerations show slightly smaller sizes than equivalent submonolayer structures grown without Sb. The structural findings are in close correlation with the different band alignments of the electronic states, showing different behavior for electrons and holes.

Room temperature operation of semiconductor nano-ring lasers fabricated through a general applicable membrane release and transfer method

A generally applicable release-transfer method is demonstrated to transfer a strained-balanced InGaAs quantum well nano-membrane of 250 nm in thickness for the fabrication of a nano-ring laser with 400 nm ring-thickness, operating at room temperature.

Self-aligned quantum-dot growth for single-photon sources

The buried oxide current-aperture in a pin diode-structure is used to create a strain field for the self-aligned nucleation of site-controlled single quantum dots. A single-photon source fabricated applying this approach shows spectrally very narrow emission lines (FWHM ≤ 25 μeV) and spectrally pure single-photon emission with a second-order autocorrelation g(2)(0) = 0.05.