Enlarged quantum well in a semiconductor superlattice studied by depth resolved grazing incidence x-ray diffraction

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Abstract
A lattice matched {InP/GaInAs}30/InP[001] superlattice containing an enlarged quantum well (EQW) was investigated by means of grazing incidence x‐ray diffraction (GID) using synchrotron radiation. The in‐plane (220) rocking curve was measured choosing a grazing angle for the incident beam with respect to the surface, αi. At the angular position of maximum intensity we recorded the intensity distribution of the reflected beam normal to the surface (rod scan) using a position sensitive detector. The rod contains information about the density variation towards the surface normal. Instead of a single superlattice Bragg peak we found a double peak which can be explained by the phase shift of the partial x‐ray waves scattered at the two superlattices sandwitching the EQW. For fixed αithe intensity ratio of the two peaks is a measure of the EQW thickness. An additional advantage of the GID technique is that this ratio can be modified by changing the penetration depth of the probing x‐ray beam into the sample. This is performed by keeping αi smaller or larger than the critical angle for total external reflection. The EQW thickness and its position below the surface is determined by simulation of the recorded rod scans using the kinematic approach of the GID. Both quantities are obtained with monolayer accuracy.