Abstract
We report a model-independent atomic-mapping technique for quantum dots (QDs) by combining Bragg reflection x-ray standing wave (XSW) and grazing incidence diffraction (GID) measurements. In this study, we choose GaAs capped InGaAs QDs/GaAs(001) as a model system to show the locations and arrangements of indium atoms within the QDs along various [hkl] directions. This technique directly reveals the actual amount of positional anisotropy and ordering fraction of indium atoms within the QDs by probing the (1¯11), (111), (311), (1¯31), (113), and (1¯13) crystallographic planes. We find that indium atoms are outwardly shifted along the [001] direction by small fractions of the lattice constant, 0.04aGaAs and 0.06aGaAs from Ga sites for 50- and 150-Å GaAs capped InGaAs QDs, respectively. We observe that an improved coherency factor of the indium atoms within the QDs by 45-60% along the [001] and [011] directions reduces the photoluminescence linewidth by 22%, thus making the QDs efficient for QD-laser and optoelectronic device applications. We also find that the position and ordering of In atoms along the (113) and (1¯13) planes are most sensitive to the thickness of the GaAs cap layer. Our XSW-based results are supported by numerical calculations using a QD-macroscopic structural model based on our GID study. We thus show that this atomic-mapping technique will be useful for studying various quantum structures and tuning their properties.
| Original language | English (US) |
|---|---|
| Article number | 056002 |
| Journal | Physical Review Materials |
| Volume | 4 |
| Issue number | 5 |
| DOIs | |
| State | Published - May 2020 |
Funding
We thank the Indo-US Science and Technology Forum (IUSSTF) for their financial support for doing experiments under the project “Crystallization at Interfaces.” This work was partially supported at Northwestern University (NU) by the Institute for Catalysis in Energy Processes (ICEP) under U.S. DOE Grant No. DE-FG02-03ER15457 and National Science Foundation MRSEC (Grant No. DMR-1720139). GID experiments at PETRA-III synchrotron DESY were carried out through the India-DESY collaboration program. XSW experiments were performed at the Argonne National Lab (ANL) Advanced Photon Source (APS) DND-CAT 5ID-C station. ANL is supported by the DOE under Grant No. DE-AC02-06CH11357. DND-CAT is supported through E. I. DuPont de Nemours & Co., Northwestern University, The Dow Chemical Co., and the NSF funded MRSEC at NU. Preliminary and calibration measurements made use of the NU X-ray Diffraction Facility supported by the MRSEC.
ASJC Scopus subject areas
- General Materials Science
- Physics and Astronomy (miscellaneous)