Transmission electron microscopy of AlGaAs/GaAs quantum cascade laser structures

T Walther; A B Krysa

doi:10.1111/jmi.12655

Transmission electron microscopy of AlGaAs/GaAs quantum cascade laser structures

J Microsc. 2017 Dec;268(3):298-304. doi: 10.1111/jmi.12655. Epub 2017 Oct 3.

Authors

T Walther^{1

2}, A B Krysa^{3

2}

Affiliations

¹ Kroto Centre for High Resolution Imaging and Analysis, University of Sheffield, Sheffield, U.K.
² Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield, U.K.
³ EPSRC National Centre for III/V-Technologies, University of Sheffield, Sheffield, U.K.

PMID: 28972657
DOI: 10.1111/jmi.12655

Abstract

Quantum cascade lasers can be efficient infrared radiation sources and consist of several hundreds of very thin layers arranged in stacks that are repeated periodically. Both the thicknesses of the individual layers as well as the period lengths need to be monitored to high precision. Different transmission electron microscopy methods have been combined to analyse AlGaAs/GaAs quantum cascade laser structures in cross-section. We found a small parabolic variation of the growth rate during deposition, affecting the stack periodicity and a reduced aluminium content of the AlGaAs barriers, whereas their widths as well as those of the GaAs quantum wells agreed with the nominal values within one atomic layer. Growth on an offcut substrate led to facets and steps at the interfaces.

Keywords: Annular dark-field scanning TEM; Z-contrast; composition mapping; high-resolution electron microscopy; quantum cascade laser (QCL); transmission electron microscopy (TEM).