X-ray standing-wave study of(AlAs)m(GaAs)nshort-period superlattices

Abstract

X-ray standing-waves (XSW) are used for an investigation of the structure of $(\mathrm{AlAs}{)}_{m}(\mathrm{GaAs}{)}_{n}$ short-period superlattices (SL's). The XSW induced modulation of x-ray fluorescence from the Al, As, and Ga atoms and the total photoelectron yield are monitored around the 0th order SL satellite (AlAs)(GaAs)(004,0) and the GaAs(004) substrate Bragg reflection. From the specific shape of these modulations and the sample reflectivity, an atomic model about the interfaces is derived. This is accomplished by comparing the experimental data with dynamical calculations of x-ray wavefield distribution and reflectivity, which are based on the Takagi-Taupin equation. The fluorescence measurements at the 0th order SL satellite reveal a high crystalline order in the AlAs layers of the short-period SL, whereas in the GaAs layers, a fraction of the Ga and As atoms is not on the ideal lattice positions. From the analysis, a model of the atomic distribution along the [001] direction can be determined. This reveals that at each internal interface in the GaAs layers, two Ga atom planes are shifted by up to 0.035 nm and one As atom plane by 0.023 nm. At each interface, the shifts are directed towards the substrate. In addition, the XSW field at the GaAs(004) substrate reflection results in a moir\'e or beating effect in the SL structure, which can be used to determine the information depth ${\ensuremath{\Lambda}}_{e}$ of total electron-yield measurements in a more detailed approach.