  The effect of Gamma-X mixing on the energy levels fine structure of indirect
in k-space excitons in an ensemble of (In,Al)As/AlAs quantum dots with type I
band alignment was experimentally studied. Using the methods of optical spin
orientation and optical alignment in a magnetic field, an increase in the
anisotropic exchange splitting of excitonic levels (from approximately 0.6 to 5
ueV) due to the Gamma-X mixing was revealed. The extent of direct electronic
states admixing to indirect ones depends on the size of the quantum dot. On the
other hand, the optical and spin properties of excitons change radically with
increasing of the Gamma states admixture to the X states: in the absence of a
magnetic field, the optical orientation of excitons decreases from 18 to 3%,
while the alignment of excitons is restored from 6 to 53%.
