  The dynamics of exciton recombination in an ensemble of indirect band-gap
(In,Al)As/AlAs quantum dots with type-I band alignment is studied. The lifetime
of confined excitons which are indirect in momentum-space is mainly influenced
by the sharpness of the heterointerface between the (In,Al)As quantum dot and
the AlAs barrier matrix. Time-resolved photoluminescence experiments and
theoretical model calculations reveal a strong dependence of the exciton
lifetime on the thickness of the interface diffusion layer. The lifetime of
excitons with a particular optical transition energy varies because this energy
is obtained for quantum dots differing in size, shape and composition. The
different exciton lifetimes, which result in photoluminescence with
non-exponential decay obeying a power-law function, can be described by a
phenomenological distribution function, which allows one to explain the
photoluminescence decay with one fitting parameter only.
