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

X-ray standing-waves (XSW) are used for an investigation of the structure o f (AlAs)(m)(GaAs)(n) short-period superlattices (SL's). The XSW induced mod ulation of x-ray fluorescence from the Al, As, and Ga atoms and the total p hotoelectron yield are monitored around the 0th order SL satellite (AlAs)(G aAs)(004,0) and the GaAs(004) substrate Bragg reflection. From the specific shape of these modulations and the sample reflectivity, an atomic model ab out the interfaces is derived. This is accomplished by comparing the experi mental data with dynamical calculations of x-ray wavefield distribution and reflectivity, which are based on the Takagi-Taupin equation. The fluoresce nce measurements at the 0th order SL satellite reveal a high crystalline or der 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. Fr om the analysis, a model of the atomic distribution along the [001] directi on can be determined. This reveals that at each internal interface in the G aAs layers, two Ga atom planes are shifted by up to 0.035 nm and one As ato m plane by 0.023 nm. At each interface, the shifts are directed towards the substrate. Ln addition, the XSW field at the GaAs(004) substrate reflectio n results in a moire or beating effect in the SL structure, which can be us ed to determine the information depth Lambda e of total electron-yield meas urements in a more detailed approach. [S0163-1829(99)12715-2].