Laterally modulated composition profiles in AlAs/InAs short-period superlattices

Laterally modulated composition profiles in AlAs/InAs short-period superlattices grown by molecular-beam epitaxy under tensile strain on (001) InP are examined by transmission electron microscopy (TEM) and x-ray diffraction K mapping. Weak, one-dimensional modulation with a wavelength of lambda(m) = 110 Angstrom is observed for a period of 1 ML. At 2 ML, the composition profile is irregular, while a two-dimensional network of wire and dot structures with lambda(m) = 130 Angstrom occurs at 3 ML. At a high growth rate, 4-ML samples exhibit smooth modulated profiles with lambda(m) = 220 Angstrom. When the growth rate is reduced with beam interrupts, sharp profiles develop that show strong alignment in the substrate plane with lambda(m) = 270 Angstrom. TEM dark-field image contrast of the modulated profiles is simulated using dynamical diffraction theory to reproduce features observed in experiment. (C) 1998 American Institute of Physics. [S0021-8979(98)02123-9].