Complete characterization of GaAs gradient-elastic tensors and reconstruction of internal strain in GaAs/AlGaAs quantum dots using nuclear magnetic resonance

Recently, we have calibrated the diagonal components S11=Sxxxx of the GaAs gradient elastic tensor Sijkl using nuclear magnetic resonance (NMR) and photoluminescence spectroscopy of GaAs/AlGaAs quantum dot structures in Faraday geometry [E. A. Chekhovich et al., Phys. Rev. B 97, 235311 (2018)]. Here we measure quantum dot NMR spectra in oblique magnetic fields giving access to the off-diagonal components Syzyz. We find the ratios Syzyz/Sxxxx≈+1.98+0.21−0.27 for 75As and ≈−0.40+0.23−0.31 for 69Ga. Combined with our previous results, we find all independent nonzero components of Sijkl: QSxxxx≈+0.758×10−6 V, QSyzyz≈+1.51×10−6 V for 75As and QSxxxx≈−0.377×10−6 V, QSyzyz≈+0.151×10−6 V for 69Ga, where Q is the corresponding nuclear quadrupolar moment. Our results show that earlier nuclear acoustic resonance experiments [R. K. Sundfors, Phys. Rev. B 10, 4244 (1974)] most likely overestimated the GaAs gradient elastic tensors, especially for 69Ga. We further use NMR spectroscopy in oblique fields for assumption-free measurement of the intrinsic strain in GaAs/AlGaAs quantum dots. We find deviations of the strain principle directions from the sample growth axis, which vary between individual quantum dots.