Growth and Characterization of Ultrathin InAs/GaAs and GaSb/GaAs Quantum Wells

GaSb/GaAs and InAs/GaAs multiple quantum wells are grown by organometallic vapour phase epitaxy and characterized by x-ray diffraction, transmission electron microscopy and photoluminescence spectroscopy. Reflectance-difference spectroscopy is used to identify a characteristic signature of Sb on the GaAs (001) surface and to show that Sb has a strong tendency to segregate to the surface. The incorporation of Sb results in a graded GaAs-on-GaSb interface which is well described by a onedimensional model with a segregation coefficient of ~ 0.95. Desorption of the surface Sb layer is enhanced by exposure to tertiarybutylarsine; the interface abruptness is dramatically increased by employing a flashoff sequence in which the accumulated Sb is desorbed prior to GaAs overgrowth. Atomic force microscope images show that the transition from planar GaSb growth on GaAs to island formation occurs for a submonolayer coverage under equilibrium conditions. If the layer is immediately capped by GaAs overgrowth, however, a monolayer of GaSb can be grown without dots forming. Low-temperature photoluminescence spectra of abrupt and graded GaSb/GaAs quantum wells are compared; the luminescence line is at a lower energy for the more abrupt structures. For InAs/GaAs quantum wells, the luminescence line is at a higher energy than for the GaSb/GaAs quantum wells. The experimentally determined transition energies are compared with calculations using the envelope function approximation.