Stacks of InAs/GaAs submonolayer depositions forming small In-rich islands are interesting for efficient optoelectronic applications due to the high areal density of localization centers and their fast carrier relaxation. The electronic confinement of charge carriers in InAs/GaAs submonolayers can be influenced by adding Sb during growth. Eight-band k . p simulations show that electrons and holes experience a different localization depending on where the Sb is incorporated into the submonolayer stacks. Samples grown with metalorganic vapor-phase epitaxy show sharp interfaces between InAs(Sb)/GaAs submonolayers and the surrounding matrix material in transmission electron microscopy and x-ray diffraction measurements. Cross-sectional scanning tunneling microscopy shows the formation of In-rich agglomerations as well as a slight clustering of Sb atoms. Temperature-dependent photoluminescence and spatially resolved cathodoluminescence show evidence for strong electronic confinement whose depth is controlled by the Sb amount.