Multi-dimensional modeling and simulation of semiconductor nanophotonic devices

Self-consistent modeling and multi-dimensional simulation of semiconductor nanophotonic devices is an important tool in the development of future integrated light sources and quantum devices. Simulations can guide important technological decisions by revealing performance bottlenecks in new device concepts, contribute to their understanding and help to theoretically explore their optimization potential. The efficient implementation of multi-dimensional numerical simulations for computer-aided design tasks requires sophisticated numerical methods and modeling techniques. We review recent advances in device-scale modeling of quantum dot based single-photon sources and laser diodes by self-consistently coupling the optical Maxwell equations with semiclassical carrier transport models using semi-classical and fully quantum mechanical descriptions of the optically active region, respectively. For the simulation of realistic devices with complex, multi-dimensional geometries, we have developed a novel hp-adaptive finite element approach for the optical Maxwell equations, using mixed meshes adapted to the multi-scale properties of the photonic structures. For electrically driven devices, we introduced novel discretization and parameter-embedding techniques to solve the drift-diffusion system for strongly degenerate semiconductors at cryogenic temperature. Our methodical advances are demonstrated on various applications, including vertical-cavity surface-emitting lasers, grating couplers and single-photon sources

Deterministically fabricated strain-tunable quantum dot single-photon sources emitting in the telecom O-band

Most quantum communication schemes aim at the long-distance transmission of quantum information. In the quantum repeater concept, the transmission line is subdivided into shorter links interconnected by entanglement distribution via Bell-state measurements to overcome inherent channel losses. This concept requires on-demand single-photon sources with a high degree of multi-photon suppression and high indistinguishability within each repeater node. For a successful operation of the repeater, a spectral matching of remote quantum light sources is essential. We present a spectrally tunable single-photon source emitting in the telecom O-band with the potential to function as a building block of a quantum communication network based on optical fibers. A thin membrane of GaAs embedding InGaAs quantum dots (QDs) is attached onto a piezoelectric actuator via gold thermocompression bonding. Here, the thin gold layer acts simultaneously as an electrical contact, strain transmission medium, and broadband backside mirror for the QD-micromesa. The nanofabrication of the QD-micromesa is based on in situ electron-beam lithography, which makes it possible to integrate pre-selected single QDs deterministically into the center of monolithic micromesa structures. The QD pre-selection is based on distinct single-QD properties, signal intensity, and emission energy. In combination with strain-induced fine tuning, this offers a robust method to achieve spectral resonance in the emission of remote QDs. We show that the spectral tuning has no detectable influence on the multi-photon suppression with g(2)(0) as low as 2%–4% and that the emission can be stabilized to an accuracy of 4 μeV using a closed-loop optical feedback

Deterministically fabricated quantum dot single-photon source emitting indistinguishable photons in the telecom O-band

In this work, we develop and study single-photon sources based on InGaAs quantum dots (QDs) emitting in the telecom O-band. Quantum devices are fabricated using in situ electron beam lithography in combination with thermocompression bonding to realize a backside gold mirror. Our structures are based on InGaAs/GaAs heterostructures, where the QD emission is redshifted toward the telecom O-band at 1.3 μm via a strain-reducing layer. QDs pre-selected by cathodoluminescence mapping are embedded into mesa structures with a backside gold mirror for enhanced photon-extraction efficiency. Photon-autocorrelation measurements under pulsed non-resonant wetting-layer excitation are performed at temperatures up to 40 K, showing pure single-photon emission, which makes the devices compatible with stand-alone operation using Stirling cryocoolers. Using pulsed p-shell excitation, we realize single-photon emission with a high multi-photon suppression of g(2)(0) = 0.027 ± 0.005, an as-measured two-photon interference visibility of (12 ± 4)%, a post-selected visibility of (96 ± 10)%, and an associated coherence time of (212 ± 25) ps. Moreover, the structures show an extraction efficiency of ∼5%, which is comparable to values expected from numeric simulations of this photonic structure. Further improvements of our devices will enable implementations of quantum communication via optical fibers.BMBF, 13N14876, Quantenkommunikations-Systeme auf Basis von Einzelphotonenquellen (QuSecure

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

Multi-dimensional Modeling and Simulation of Semiconductor Nanophotonic Devices

Self-consistent modeling and multi-dimensional simulation of semiconductor nanophotonic devices is an important tool in the development of future integrated light sources and quantum devices. Simulations can guide important technological decisions by revealing performance bottlenecks in new device concepts, contribute to their understanding and help to theoretically explore their optimization potential. The efficient implementation of multi-dimensional numerical simulations for computer-aided design tasks requires sophisticated numerical methods and modeling techniques. We review recent advances in device-scale modeling of quantum dot based single-photon sources and laser diodes by self-consistently coupling the optical Maxwell equations with semi-classical carrier transport models using semi-classical and fully quantum mechanical descriptions of the optically active region, respectively. For the simulation of realistic devices with complex, multi-dimensional geometries, we have developed a novel hp-adaptive finite element approach for the optical Maxwell equations, using mixed meshes adapted to the multi-scale properties of the photonic structures. For electrically driven devices, we introduced novel discretization and parameter-embedding techniques to solve the drift-diffusion system for strongly degenerate semiconductors at cryogenic temperatures. Our methodical advances are demonstrated on various applications, including vertical-cavity surface-emitting lasers, grating couplers and single-photon sources