Screening effects in InAs quantum-dot structures observed by photoluminescence and capacitance-voltage spectra

We have performed photoluminescence spectroscopy as well as capacitance-voltage spectroscopy on an ensemble of self-assembled InAs quantum dots that are embedded in a field-effect-transistor structure. By investigating the charging spectra as a function of excitation power density, we are able to demonstrate a buildup of a transient positive charge in the heterostructure that leads to a screening of the electric field inside the structure. Moreover, by taking photoluminescence and capacitance spectra simultaneously, we can correlate the charging state of the dots with the interband transitions of s- and p-shell. We find that the observation of photoluminescence from higher orbital states in such field-effect-transistor structures is not only a consequence of Pauli-blocking but also of the accumulation of holes inside the structure. Also, we are able to determine the energy shift between the higher-charged excitonic states X^2- and X^3- to be ΔE=2.6 meV.