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Layer-dependent spin properties of charge carriers in vertically coupled telecom quantum dots

Marius Cizauskas1,2,*, A. Kors3, J. P. Reithmaier3, A. Mark Fox2, M. Benyoucef3,†, Manfred Bayer1, and Alex Greilich1,‡

  • *Contact author: marius.cizauskas@tu-dortmund.de
  • †Contact author: m.benyoucef@physik.uni-kassel.de
  • ‡Contact author: alex.greilich@tu-dortmund.de
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Phys. Rev. B 113, 035441 – Published 28 January, 2026

DOI: https://doi.org/10.1103/xmz7-18rg

Abstract

We investigate the spin properties of charge carriers in vertically coupled InAs/InAlGaAs quantum dots grown by molecular beam epitaxy, emitting at telecom C-band wavelengths, with a silicon δ-doped layer. Using time-resolved pump-probe Faraday ellipticity measurements, we systematically study single-, two-, and four-layer quantum dot (QD) configurations to quantify how vertical coupling affects key spin-coherence parameters. Our measurements reveal distinct layer-dependent effects: (i) Adding a second QD layer flips the resident charge from electrons to holes, consistent with optically induced electron tunneling into lower-energy dots and resultant hole charging. (ii) Starting from the four-layer sample, the pump-probe signal develops an additional nonoscillating, decaying component absent in single- and two-layer samples, attributed to multiple layer growth changing the strain environment, which reduces heavy-hole and light-hole mixing. (iii) With four layers or more, hole spin mode locking (SML) can be observed, enabling quantitative extraction of the hole coherence time T2≈13 ns from SML amplitude saturation. We also extract longitudinal spin relaxation (T1) and transverse (T2*) spin dephasing times, g-factors, and inhomogeneous dephasing parameters for both electrons and holes across all layer configurations. The hole spin dephasing times T2* remain relatively constant (2.3–2.7 ns) across layer counts, while longitudinal relaxation times T1 decrease with increasing layers (from 0.9µs for single-layer to 0.32µs for four-layer samples). These findings provide potential design guidelines for engineering spin coherence in telecom-band QDs for quantum information applications.

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Phys. Rev. B 113, 035441– Published 28 January, 2026
  • Received 18 September 2025
  • Revised 18 November 2025
  • Accepted 9 January 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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