Abstract
First, are measure the coherence time of optically oriented carrier spins in wide gap quantum wells and observe an increase with temperature from less than 10 ps at 20 K to 500 ps at 200 K. Second, we measure the temperature dependence of the momentum relaxation time by four wave mixing and absorption experiments. The spin relaxation time is approximately proportional to the inverse of the momentum relaxation time. In the low-temperature regime, the strong increase of spin lifetime can be caused by motional narrowing due to the faster scattering of excitons with increasing temperature. In the high-temperature regime, quenching of the electron-hole spin flip dephasing due to an increasing ionization of excitons with increasing temperatures can prolongate spin lifetime. (C) 1999 Elsevier Science B.V. All rights reserved.