Interfaces in AlGaSb∕GaSb multiquantum well structures

Abstract

The Al0.4Ga0.6Sb∕GaSb∕Al0.4Ga0.6Sb quantum well (QW) structures were grown by a molecular beam epitaxy on the GaSb substrates at different growth temperatures (Tg) and with different Sb4∕Ga beam equivalent pressure ratios (BEPR) and were studied using high-resolution x-ray diffraction, photoluminescence (PL), and transmission electron microscopy. The x-ray diffraction analysis showed that the AlGaSb∕GaSb interfaces have smooth Al composition profiles with graded region thicknesses in the range of 0.83nm–2.17nm, depending upon the growth conditions; the normal interfaces are generally sharper than the inverse ones. The low-temperature PL spectra from QWs show relatively broad peaks and energies of the peak emission that can be related to the growth parameters. Good agreement was obtained between the PL peak energies and the transition energies calculated using a QWs model that takes into account the one-dimensionally graded confining potential for describing the experimentally determined Al composition profiles. The interface broadening can be due to Al and Ga segregation, Al diffusion, or Al and Ga intermixing. The broadening increases with the growth conditions that enhance the surface mobility of group-III species, such as high Tg and low V∕III BEPRs. The relatively large full widths at half maxima of the PL features were attributed to the Al composition fluctuations in the barriers, instead of the well thickness ones.