Structural properties of InAs/InAs _1-xSb _x type-II superlattices

This paper describes structural properties of strain-balanced InAs/InAs _1-xSb _x type-II superlattices (SLs) with random and modulated InAs/InAs _1-xSb _x alloy layers as grown on GaSb(001) substrates either by molecular beam epitaxy (MBE) or metalorganic chemical vapor deposition. The SL periods and the average Sb compositions of the InAs/InAs _1-xSb _x alloys are determined by comparison of simulations with (004) high-resolution X-ray diffraction (XRD) measurements. The most intense SL peaks no longer correspond to the zero-order peak because of the large SL periods, and XRD studies of thick individual InAs/InAs _1-xSb _x and InAs layers show envelope modulations of the SL peaks on either side of the substrate peak, causing some satellite peaks to be more intense than the zero-order SL peak. From the substrate - zero-order SL peak separations, the average SL strain in the growth direction is revealed to be less than ∼0.2%. Calculated bandgap energies agree closely with photoluminescence peaks for mid-wavelength and long-wavelength infrared samples. Cross-sectional electron micrographs reveal the entire structure including the GaSb substrate and buffer layer, the SL periods, and the GaSb cap layer. Growth defects are occasionally visible, some originating at the substrate/buffer interface, some starting in the middle of the buffer layer, and some located only just within the SL. Higher magnification images of the SLs grown by MBE reveal that interfaces for InAs/InAs _1-xSb _x deposited on InAs are considerably more abrupt than those of InAs deposited on InAs/InAs _1-xSb _x with the most likely reason being segregation of the Sb surfactant during layer growth.