Evolution from individual to collective electron states in a dense quantum dot ensemble

Absorption spectrum of a quantum dot ensemble was found to exhibit a systematic modification with dot concentration from a set of discrete subbands inherent in isolated nanocrystals to a smooth band-edge absorption similar to that of bulk semiconductors. The results are interpreted in terms of an evolution from individual (localized) to collective electron states delocalized within at least a finite number of nanocrystals. The observed behavior is considered as a possible precursor of the Anderson transition in a quantum dot ensemble, i.e., a transition from localized electron states to states that are delocalized over a macroscopically large number of nanocrystals. [S0163-1829(99)01327-2].