Can we distinguish between misfit and threading dislocations using x-ray diffuse scattering experiment? The case of PbTe thin layers.

S. Daniš and V. Holý

Department of Electronic Structures, Faculty of Mathematics and Physics, Charles University Prague,

Ke Karlovu 5, 121 16 Prague 2, Czech Republic

e-mail:danis@mag.mff.cuni.cz

X-ray diffuse scattering is a commonly used tool for determination of real structure in monocrystals, powders and low dimensional systems. If there is only one type of defect in the sample (clusters of atoms in ion-bombarded silicon, for example), the situation is quite simple. The size and concentration of the defect can be determined by reciprocal space maps. However, in the case of relaxed heteroepitaxial thin layers, we have to deal with misfit and threading dislocations.

Intensity of diffuse x-ray scattering is given by displacement of atoms caused by the defect(s). The displacement fields are simulated within isotropic theory of elasticity. The total intensity is calculated within kinematical theory of x-ray scattering,

where A is, among others, a constant containing square of the sample polarizability, V is the layer volume, q = Q-h is the coordinate in reciprocal space relative to the reciprocal lattice point h, Q = K_f -K_i is the scattering vector. T_h(r,r’) is correlation function of defects defined as a sum of contribution from threading and misfit dislocations,

Diffuse x-ray scattering from epitaxial PbTe layer on Si(111) is analyzed both theoretically and experimentally. Reciprocal space maps (RSM) and x-ray diffraction profiles are measured and simulated for symmetrical and asymmetrical diffractions. The intensity distribution of diffusively scattered radiation is simulated within statistical theory of x-ray scattering [1,2]. Both types of expected defects -misfit and threading dislocations – will be discussed.

[1] M. A. Krivoglaz, X-Ray and Neutron Diffraction in Nonideal Crystals, (Springer Berlin 1996)

[2] V. M. Kaganer, R. Koehler, M. Schmidbauer, R. Opitz, and B. Jenichen, Phys. Rev. B 55, 1793 (1997).