INVESTIGATIONS OF SEMICONDUCTOR SUPERLATTICES BY DEPTH-SENSITIVE X-RAY-METHODS

Focusing on the structure determination of a GaInAs/InP superlattice ( SL), the potential of grazing incidence diffraction (GID) to resolve s tructure parameters on a microscopic scale is compared to x-ray reflec tivity and conventional x-ray diffraction (XRD) measurements. Usually, information on the density profile perpendicular to the surface is ob tained by x-ray reflectivity and on lattice mismatch by XRD. Since the penetration depth of x rays is much larger than the total thickness o f the SL these methods measure parameters averaged over the whole stru cture. Furthermore, the depth sensitivity of both methods is small in the case of extremly high thickness ratios of the sublayers within the SL period. These disadvantages can be overcome using GID geometry for which the information depth can be reduced by keeping the angle of in cidence alpha(i) and exit alpha(f) of the x-ray beam with respect to t he surface in the range close to the critical angle of total external reflection alpha(C). This enables a depth-selective structure determin ation. As an example measurements and computer simulations correspondi ng to the three different methods of a lattice-matched (GaIn)As/InP SL are presented. The periodic length of the present SL and the thicknes s of the top layer was determined by all three methods to monolayer ac curacy.