Microsecond Lifetime of Exciton Spin Polarization in (In,Al)As/AlAs Quantum Dots

The time of spin relaxation of excitons in (In,Al)As/AlAs quantum dots with an indirect bandgap and type-I band alignment is determined by measuring the dynamics of photoluminescence circular polarization induced by a magnetic field B. The spin relaxation time τ S increases with decreasing magnetic field in proportion to B −5; its value is ∼40 µs in a magnetic field of 6 T at a temperature of 1.8 K. As the temperature T increases in a magnetic field of 7 T, the value of τ S decreases as T −1.1. The character of the dependences of τ S on the magnetic field and temperature evidences that spin relaxation of excitons is provided by a process with participation of one acoustic phonon.