X-ray diffraction analysis of GaInNAs double-quantum-well structures

The structures of GaInNAs/GaAs double-quantum-well (DQW) samples with various well-layer thicknesses were analysed by X-ray diffraction measurements. Two types of rocking-curve analysis were applied with different scanning configurations: a conventional configuration without a receiving slit and one with an analyser crystal placed in front of the receiving detector (the latter is the same as that usually used in reciprocal-space mapping measurements). It was found that systematic combination of both types of analysis is essential for the characterization of the sample structures. The two types of X-ray profiles obtained using the different scanning configurations exhibit a considerable difference in intensity as the thickness of the well layers increases. The increasing difference clearly indicates deterioration of the DQW structures. The two profiles exhibit little difference in terms of shape, merely showing that the DQW layers are coherently strained relative to the substrate. This implies that measurement in only one of the configurations is insensitive to the deterioration and leads to the wrong conclusion that a sample has a perfect structure without dislocations and defects. Photoluminescence and transmission electron microscope analyses both reveal that defects really do exist in the DQW structures, which is consistent with the difference in intensity observed in the X-ray measurements. From these results, a clear picture that consistently explains the sensitivity of X-ray diffraction analysis to the deterioration of samples is presented. In addition, based on this picture, it is proposed that the procedure of comparing the two types of profiles represents a new type of analysis method for the precise characterization of samples.