Measurement of indium segregation in strained InxGa1-xAs/GaAs quantum wells by transmission electron microscopy

  1. Get@NRC: Measurement of indium segregation in strained InxGa1-xAs/GaAs quantum wells by transmission electron microscopy (Opens in a new window)
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Journal titlePhilosophical Magazine A.
Pages803821; # of pages: 19
Subjectquantum wells; indium segregation; transmission electron microscopy (TEM); double-crystal X-ray diffraction (DCXRD)
AbstractDuring the production of InxGa1-xAs quantum wells by the crystal growth technique of molecular beam epitaxy, the indium tends to accumulate in the surface layer and to float on the crystal growth surface. This effect delays incorporation of the indium into the quantum well and results in a graduated value of x across the well. Detailed indium concentration profile information is essential if accurate theoretical models are to be applied to describe these quantum wells. Therefore, to quantify this indium segregation we combine the complementary results of two experimental techniques: transmission electron microscopy (TEM) and double-crystal X-ray diffraction (DCXRD). The indium concentration well profiles were determined through an analysis of the contrast variation in (200) dark-field TEM images. Differences of less than 0.5% indium concentration were discernible. The DCXRD analysis provided an accurate value for the total amount of indium in the individual wells which was used as the scaling factor for the TEM concentration profile. To ensure that the observed contrast differences were due to variations in indium concentration and were not merely TEM sample preparation artefacts, high-quality cross-sectional TEM samples with parallel cleaved surfaces free of ion-milling damage were required. Accurate thickness values for the samples were also needed. A TEM sample preparation technique was developed to provide these requirements. Indium concentration profiles were taken from intensity line scans across dark-field TEM images of these samples. These profiles were interpreted by a simple kinematical theory (structure factor) calculation, and then by a more rigorous model using the dynamical theory of electron diffraction. The results of these two models were then checked for consistency with the results of the DCXRD measurement. The model profiles of indium segregation within the quantum wells, calculated using the structure factor approach for up to 35% indium content, matched very closely the profiles produced by the use of dynamical theory. Both sets of model profiles strongly supported the DCXRD results. These results demonstrate that a simple structure factor calculation in conjunction with a DCXRD measurement can allow an accurate measure of quantum well profiles and of the abruptness of InxGa1-xAs on GaAs and GaAs on InxGa1-xAs interfaces. This information is a powerful aid in the modelling and understanding of devices based on these structures.
Publication date
AffiliationNational Research Council Canada; NRC Institute for National Measurement Standards; NRC Institute for Microstructural Sciences
Peer reviewedYes
NPARC number12328191
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Record identifier140c3b21-382c-472c-ad74-256bdacd2c4f
Record created2009-09-10
Record modified2016-05-09
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