This thesis presents time-resolved measurements of the spin evolution of transient carrier populations in III-V quantum wells. Non-equilibrium distributions of spin polarisation were photoexcited and probed with picosecond laser pulses in three samples; a high mobility modulation n-doped sample containing a single GaAs/AlGaAs quantum well, an sample containing three quantum wells and, a multi-period GaAs/AlGaAs narrow quantum well sample. | UNIVERSITY OF SOUTHAMPTON Optical time resolved spin dynamics in III-V semiconductor quantum wells by Matthew Anthony Brand A thesis submitted for the degree of Doctor of Philosophy at the Department of Physics August 2003 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF SCIENCE Doctor of Philosophy Optical time resolved spin dynamics in III-Vsemiconductor quantum wells Matthew Anthony Brand This thesis presents time-resolved measurements of the spin evolution of transient carrier populations in III-V quantum wells. Non-equilibrium distributions of spin polarisation were photoexcited and probed with picosecond laser pulses in three samples a high mobility modulation n-doped sample containing a single GaAs AlGaAs quantum well an GaAs sample containing three quantum wells and a multi-period GaAs AlGaAs narrow quantum well sample. Electron spin polarisation in low mobility wells decays exponentially. This is successfully described by the D yakonov-Perel DP mechanism under the frequent collision regime within which the mobility can be used to provide the scattering parameter. This work considers the case of a high mobility sample where collisions are infrequent enough to allow oscillatory spin evolution. It is shown however that in n-type quantum wells the electron-electron scattering inhibits the spin evolution leading to slower non-oscillatory decays than previously expected. Observed electron spin relaxation in InGaAs InP is faster than in GaAs AlGaAs. This may be ascribed to an enhanced DP relaxation caused by Native Interface Asymmetry NIA in InGaAs InP or to the differing natures of the well materials. Here the two possibilities have been distinguished by measuring electron spin relaxation in InGaAs GaAs quantum wells. The long spin lifetime implicates the NIA as the cause of the fast relaxation in InGaAs InP. Finally the reflectively probed optically induced linear birefringence method has been used to measure quantum beats between the heavy-hole .
