Theory of optical responses of spherical quantum dots under static and dynamical external fields

The influence of an external electric charge on optical properties of a spherical quantum dot (QD) is theoretically investigated within the effective-mass approximation. The absorption spectrum of QD is strongly affected when the electric charge Approaches close to the surface of QD : the lowest excited state shows a rapid red-shift and partially loses its oscillator strength. The magnitude of the red-shift and the reduction rate of the oscillator strength in such a case shows a characteristic change as a function of the dot-size : the former monotonously increases as the dot-size is reduced; while the latter reaches its maximum when the dot-size corresponds to that of the intermediate confinement regime.