Quantitative characterization of the interface roughness of (GaIn)As quantum wells by high resolution STEM.

The physical properties of semiconductor quantum wells (QW), like (GaIn)As/GaAs, are significantly influenced by the interface morphology. In the present work, high angle annular dark field imaging in (scanning) transmission electron microscopy ((S)TEM), in combination with contrast simulation, is used to address this question at atomic resolution. The (GaIn)As QWs were grown with metal organic vapor phase epitaxy on GaAs (001) substrates under different, precisely controlled conditions. In order to be able to compare different samples, a carefully applied method to gain reliable results from high resolution STEM micrographs was used. The thickness gradient of the TEM samples, caused by sample preparation, was compensated by the intensity of group V atomic columns, where no alloying takes place. After that, the In concentration map was plotted for the investigated regions based on the intensity of the group III atomic columns. The composition maps show that the Indium distribution across the quantum well is not homogeneous. The growth temperature of the QW can greatly influence the composition fluctuation and the interface morphology, with higher growth temperature resulting in larger composition fluctuations in the QWs and slightly wider interfaces, i.e. larger In-segregation. Growth interruptions are shown to significantly homogenize the elemental depth profile especially along the (GaIn)As/GaAs interface and hence have a positive effect on interface smoothness.