Channeling studies in strained-layer epitaxial structures

The use of planar and axial channeling to measure the magnitude of the tetragonal distortion (and hence the strain) in simple strained-layer systems has been investigated. The test structures consisted of a 250 Å epitaxial InxGa1−xAs layer sandwiched between a (100) GaAs substrate and a thin (250–360 Å) surface GaAs epilayer. The In concentrations were sufficiently high (0.10–0.16) so that the resulting tilt or kink angle, Δ, at the buried interface exceeded the planar critical angle ψc for the 2.0 MeV4He+ beam. Complications in the observed axial and planar angular scans in the InGaAs layer have been studied in detail and suitable methods for extracting the correct values of Δ have been established. Planar channeling measurements, corrected for specular reflection effects in the GaAs surface layer, give Δ values in very good agreement with those calculated from the indium content. Axial channeling, however, can only be used to determine Δ when the surface GaAs overlayer is thinner than d/ψc, where d is the spacing between atomic strings.