High Resolution Studies of Layers and Interfaces

When quantum wells are introduced into the active region of a laser device, it is especially important that their dimensions and composition be very carefully controlled so that device operation is within specified tolerances. In some cases, the well dimensions are so small that they require the growth technique to be extended to its limits: then, control over the detailed well properties is likely to be restricted. In the experiments reported here, approximately 1.8nm wide InGaAs wells were grown in an AlGaAs matrix by metal-organic chemical vapour deposition (MOCVD). The sharpness of the wells was not determined due to their very small dimensions.

Therefore, they were examined by bright-field and EFI imaging to determine their structural properties. The figure shows that the wells had good structural integrity despite their small thickness. Elemental mapping carried out by EFI imaging yielded the Ga and In profiles shown in sections b and c of the figure which, again resolve the wells. The latter clearly demonstrate the increase in concentration of In the wells from zero percent in the surrounding AlGaAs. The Ga concentration also rises in the wells in accordance with growth expectations. The EFI elemental mapping technique has a resolution of ~1nm and is effective in assessing and analyzing even the very narrow quantum wells investigated here.

a) bright-field image of quantum wells, b) In profile across wells and c) Ga profile across wells