Longitudinal Spin Relaxation Time Of Donor-Bound Electrons In A Cdte Quantum Well

We study the magnetic-field dependence of the longitudinal spin relaxation time T-1 of donor-bound electrons placed in the middle of an 8-nm CdTe quantum well with different doping concentrations in the range from 1 x 10(9) to 2.9 x 10(11)( )cm(-2) and at low temperature. We use an extended photoinduced Faraday rotation technique, which expands the usual domain of the measured decays from tens of ns to mu s. As in high-purity bulk semiconductors, a maximum relaxation time of around T-1 similar to 10 mu s is observed for a residually doped sample at low magnetic field of B = 0.08 T. For higher doping concentrations, the magnetic-field dependence of T-1 shows a nonmonotonic behavior: first a rapid increase, followed by a plateau or a decrease of T-1. The fast increase of T-1 at low magnetic fields is explained by the inhibition of the mechanisms identified at zero field-hyperfine and anisotropic exchange interactions-while the behavior at high magnetic field can be succesfully explained by a mechanism proposed by Lyubinskiy and associated to electron hops [I. S. Lyubinskiy, JETP Lett. 88, 814 (2008)]. A good agreement between experiment and theory is found for samples below the metal-insulator transition, when Dresselhaus terms of spin-orbit coupling are considered to be the dominant ones in the Hamiltonian describing the system.