Layer-thickness dependence of the compositions in strained III–V superlattices by atom probe tomography

B. Knipfer*, A. Rajeev, D. Isheim, J. D. Kirch, S. E. Babcock, T. F. Kuech, T. Earles, D. Botez, L. J. Mawst

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

In order to conduction-band engineer quantum cascade lasers (QCLs) for emission wavelength, specifically QCLs emitting at 4.6 µm, precise control over layer thicknesses and compositions is required. In this study, Al/Ga incorporation in a strain-balanced InAlAs/InGaAs superlattice (SL) on InP is characterized as a function of layer thickness, keeping the composition constant, using high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) and Atom Probe Tomography (APT). A SL structure was grown on an InP substrate by organometallic vapor phase epitaxy (OMVPE) at a temperature of 605 °C and a reactor pressure of 100 torr, with 5 sec interruption time between layers. The full growth thickness obtained from STEM images was used to calibrate the reconstruction of the atom probe data. From the APT results it was found that the Al and Ga incorporation in thin layers (<2 nm) is significantly lower (down by as much as 10–15% for 1 nm-thick layers) than the targeted composition, which results in a red-shifted emission wavelength when compared to theoretical-model calculations. This result is further shown to be self-consistent at these compositions when compared to a full QCL structure. By introducing an Al overshoot of 5% in the OMVPE gas phase Al/In ratio for the thinnest barrier layers of a full QCL structure, the emission wavelength was reduced from 4.8 µm to 4.6 µm, in accordance with the modeled wavelength for the design target.

Original languageEnglish (US)
Article number125550
JournalJournal of Crystal Growth
Volume535
DOIs
StatePublished - Apr 1 2020

Keywords

  • A1. Atom probe tomography
  • A3. Organometallic vapor phase epitaxy
  • A3. Superlattice
  • B3. Quantum cascade lasers

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Inorganic Chemistry
  • Materials Chemistry

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