We have investigated InAs quantum dots (QDs) on GaAsSb barrier layers. Low temperature photoluminescence (PL) for InAs/GaAsSb with various δ-doping levels is performed to observe interband transitions. PL spectra of heavily doped QD samples show that the electrons injected from the δ-doping plane increase the intensity of the emission peak between the electron and hole first excited states, E1H1, not observed from undoped and lightly QD samples. Time resolved photoluminescence (TRPL) data as a function of δ-doping density reveal that the introduction of a δ-doping plane in the GaAsSb barrier decreases a carrier lifetime making recombination between ground states in QD area faster. As an evidence of carriers more injected from a δ-doping plane an Arrhenius fitting curve taken from temperature dependent PL indicates that the doped samples have the greater thermal activation energies than those of the lightly doped samples. Additionally, intersubband transitions of 20 multiple InAs QDs embedded in GaAsSb barriers are experimentally determined by low temperature (77K) Fourier Transformation-Infrared Spectroscopy (FT-IR) using a multiple internal reflection technique. It is noted that there is a broad peak around about 240meV corresponding to the energy separation between the electron ground state and the continuum state in the conduction band offset (CBO). The band structure based upon an eight band k.p method confirms the experimental results observed here. Furthermore, all related physical phenomena will be discussed as well.