Evaluation of atomic exchange in interfaces by tetragonal distortion measurements
General structure of the samples. Each sample contains three strained GaAs quantum wells separated by GaP barriers which are thick enough to avoid interactions between contiguous wells.
Experimental values of (squares) and (circles) phonon modes in strained GaAs quantum wells, and calculated values for wells with sharp interfaces (dotted lines) and smooth interfaces (solid lines).
HRTEM image of a region containing a single GaAs quantum well with a nominal thickness of five atomic layers. The approximate location of interfaces is indicated by lines.
Profile related to changes on thickness and chemical composition calculated with the QUANTITEM approach (a) and distances between contiguous (002) planes (b) for the image in Fig. 3. The former approach is appropriate for measuring the sample thickness in this samples while the latter method is more accurate to measure changes in chemical composition for the system.
Experimental HRTEM image (a) and parameters to be measured: distances between atomic rows ; (002) planes ; and angles between bonds . Local intensity maxima are shown in (b). Multiple maxima related to single rows are collapsed by expanding local maxima (c). The position of the atomic rows is calculated as the center of masses of the expanded areas in (c) weighted to the intensity of the experimental image (a).
HRTEM image of a section of the sample containing quantum wells with a nominal thickness of five atomic layers (a). Mapping of atomic row distances (b), angles between bonds (c), and distances between (002) planes (d).
Distances between the centers of dumbbells in a HRTEM image (right) as a function of distances between atomic planes (left). The introduction of a single atomic layer of a material which changes the separation of layers in is followed by an asymmetric distortion of distances between 1–2 and 2–3 dumbells.
Experimental arsenic profile of a GaAs quantum well with a nominal thickness of . Note the asymmetric shape that suggest that an interdiffusion takes place mainly by an atomic exchange mechanism.
Experimental As profiles for the GaAs quantum wells with a nominal thickness of three, five, and six atomic layers (solid bars) and best fit of the atomic exchange model. The fittings give segregation coefficients close to 0.45.
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