Exciton ionization in semiconductors

Two theoretical approaches, a dynamic density-matrix approach and an equilibrium Monte-Carlo technique, are combined to give new insight into the ionization behaviour of incoherent excitons in direct-gap semiconductor heterostructures. In contrast to the widely spread picture of the excitonic Mott transition as an unbinding transition where the correlation length of a bound electron-hole pair gradually increases until an ionized plasma is formed, the number of incoherent excitons is found to decrease continuously while the mean separation between electrons and holes within the remaining bound pairs is hardly changed, i.e., the pairs remain well correlated. In fact, the remaining excitons have a mean electron-hole separation even below that of an isolated single pair. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.