Diffraction-anomalous-fine-structure spectroscopy applied to the study of III-V strained semiconductors

The effect of built-in strain on III-V epitaxial semiconductors has been investigated by extended diffraction anomalous fine structure (EDAFS) at the Ga and As K edges. A general formalism is presented for analyzing the diffraction-anomalous-fine-structure (DAFS) oscillations, valid for any type of crystallographic structure. The EDAFS spatial selectivity provides a unique tool for studying systems that are out of the reach of other x-ray techniques. We study two different systems grown on a GaAs(001) substrate: a strained layer superlattice of (GaP)(2)(InP)(3) and three single epilayers of GaAs1-xPx (x = 0.20-0.23) partially relaxed, with a different amount of residual strain. The bond distance Ga-P in the SLS is stretched by about 0.04 Angstrom in agreement with the predictions of the elastic theory. The Ga-As and Ga-P bond lengths in GaAs1-xPx remain very close to their respective bulk values, independent of the residual strain. The GaAs1-xPx epilayers have also been measured by switching the light polarization vector from the [110] to the [1 (1) over bar 0] crystallographic direction. An effect is observed on the EDAFS at the Ga K edge for the most strained sample, suggesting an ordering of the P atoms in the [001] growth direction. We also point out the interest of the DAFS spectra analysis for obtaining further information about the average crystallographic structure. [S0163-1829(99)06307-9].