Quantum confinement effects in opto-electronic materials have typically been limited to onedimensional confinement due to the constraints of epitaxial growth techniques. One method of forming higher degrees of confinement is the spontaneous lateral modulation seen in InAlAs shortperiod superlattices (SPS) grown on InP(00l). Here, a small number of monolayers (0.5 ˜ 2) of InAs and AlAs is alternately deposited by MBE to build a layer that exhibits lateral modulation on the 10 ˜ 25 nm scale. These materials show strong polarization and a large red shift (˜500meV) of the photo-emission spectra.
A key to understanding and predicting the properties of these films is determining their composition distribution. Using an HB-501 STEM, we have investigated the detailed composition distribution within a strongly modulated sample. The sample was grown in slight tension with respect to the InP substrate, a condition in which lateral modulation is known to be strong. Figure 1 shows a highangle annular dark-field (HAADF) image together with an intensity line scan from the image.