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Lucie Leguay, MSc. profile photo

Lucie Leguay, MSc.

Technical University Berlin – Institute of Solid State Physics

Evolutionary inverse design numerical approaches for improved III-Sb devices

III-Sb semiconductor materials cover a huge range of possible nanostructures, starting from compressively strained type-II GaSb/GaAs quantum dots (QDs) or, if the roles are interchanged, tensile strained GaAs/GaSb QDs, to Sb-containing QDs on other substrates such as GaP, just to mention a few examples. Owing to the large space of possible III-Sb heterostructures, applications include memory cells, lasers, LIDAR, detectors in the infra-red range, or quantum light sources. However, large parts of the opportunities linked to the III-Sb are either unexplored or even unknown, which led us look for a systematic approach to find optimal solutions for given target properties, namely the inverse design method.

Our approach is to employ evolutionary strategies to systematically scan the configuration space for optimal design candidates. The configuration space is spanned by the morphological parameters describing the nanostructure in question. In our case the parameters are comprised of size, shape, chemical composition, and growth axis of quantum dots. The associated target properties could be a given wavelength and maximal oscillator strength or wave function overlap, respectively, at this wavelength, or – if memory cells are looked for – hole localization energies respective retention times. The prospective software module will be equipped with an open, generic interface to nextnano++ (provided by NEXTNANO) and tiberCAD (provided by TiberLab).

The evolutionary strategy is not only applicable to inverse design but also to the inverse bandstructure problem. Here, the target properties are replaced by measured spectroscopic signatures of existing samples and the task is to narrow down possible nanostructures that could yield such spectra. Thus, expensive high-resolution TEM/STM characterization could be avoided.


Electronic structure of GaSb/AlGaSb quantum dots

(collaboration with the University of Tampere)

Epitaxially-grown semiconductor quantum dots (QDs) provide an attractive platform for the development of deterministic sources of high-quality quantum states of light. Such non-classical light sources are essential for quantum information processing and quantum communication. QDs emitting in the telecom wavelengths are especially important for ensuring compatibility with optical fiber systems required to implement quantum communication networks. To this end, GaSb QDs fabricated by filling local-droplet etched nanoholes are emerging as a viable approach, yet the electronic properties of such nanostructures have not been studied in detail. In this article, an insight into the electronic structure and carrier dynamics in GaSb/AlGaSb QDs is provided through a systematic experimental analysis of their temperature-dependent photoluminescence behavior. A steady-state rate equation model is used to reveal the relevant energy barriers for thermally activated carrier capture and escape processes. Furthermore, results of detailed theoretical simulations of quantum-confined energy states using the multi-band k·p model and the effective mass method are presented. The purpose of the simulations is to reveal the direct and indirect energy states, carrier wavefunctions, and allowed optical transitions for GaSb QDs with different physical dimensions.

L. Leguay et al, Unveiling the electronic structure of GaSb/AlGaSb quantum dots emitting in the third telecom window, Materials for Quantum Technology (2024).


Optimization of UV LED design using evolutionary algorithms

We present a computational approach combining evolutionary algorithms with calculation software nextnano++ to optimize the design of a nitride-based ultraviolet light-emitting diode (UV LED). Our findings reveal a significant improvement of the theoretical internal quantum efficiency of the nanostructure at the target wavelength 300 nm.

L. Leguay et al, Optimization of UV LED design using evolutionary algorithms, IEEE Photonics conference proceedings (2023).


GaSb/GaAs quantum-ring single-photon LEDs

(collaboration with the University of Lancaster)

Advances in single-photon sources have proved pivotal to the progress of quantum information processing and secure communication systems. This study addresses the imperative need for developing commercially viable, electrically-driven single-photon sources capable of operating at or above room temperature with rapid response times and emission in the telecom wavelength range of 1260 to 1675 nm. We introduce an innovative single-photon light-emitting diode (SPLED) design employing GaAs quantum dots (QDs) and self-assembled GaSb quantum rings (QRs). The core of our design is an electron filter layer composed of GaAs QDs embedded in AlxGa1-xAs, engineered to inject (single) electrons into an ensemble of type-II GaSb QRs in GaAs, where they recombine with strongly confined holes producing (single) photons at a wavelength governed by an optical cavity created using distributed Bragg reflectors (DBRs). This concept removes the need to select individual QD emitters, rendering the device highly suitable for scalable production. Our research demonstrates a comprehensive theoretical and experimental analysis using nextnano++ simulations and fabricated prototype device characteristics. Quite remarkably, we find that the emission properties of the SPLED devices actually improves as operational temperature is increased from 20 °C to 80 °C, making them attractive as practical devices.

G. Acar, L. Leguay et al, Towards GaSb/GaAs quantum-ring single-photon LEDs: recent progress and prospects, Proceedings Volume 12906, 1290609 (2024)