Electron distribution and level occupation in an ensemble of In_xGa_1-xAs/GaAs self-assembled quantum dots

We presented capacitance-voltage characteristics and electron-filling reflectance measurements to investigate electron distribution in In_0.5Ga_0.5As self-assembled quantum dot ensemble. First, the electronic structures of the quantum dots were constructed by capacitance-voltage profile. Coulomb charging effects on the electronic structures were also discussed. Then, the electron level occupations were investigated by the electron-filling reflectance spectra. Due to the correlated carrier transfer among the quantum dots and the n-type GaAs environment, the electron level filling is found to be inhomogeneous near the Fermi level. Finally, electron thermal population in the quantum dot levels was also investigated. The activation energies for the thermal population were found to be close to the level splitting. This means that electrons thermally populated to higher state do not require Coulomb charging energy.