Electron spin beats in InGaAs GaAs quantum dots

Time-resolved picosecond spectroscopy is used for the first time to study o ptical orientation and spin dynamics of carriers in self-organized In(Ga)As /GaAs quantum-dot (QD) arrays. Optical orientation of carriers created by 1 .2 ps light pulses, both in the GaAs matrix and wetting layer, and captured by QDs is found to last a few hundreds of picosecond. The saturation of el ectron ground state at high-excitation-light intensity leads to electron po larization in excited states close to 100% and to its vanishing in ground s tate. Electron-spin quantum beats in a transverse magnetic field are observ ed for the first time in semiconductor QDs. We thus determine the quasi-zer o-dimensional electron g factor in In0.5Ga0.5As/GaAs QDs to be: \g(perpendi cular to)\ = 0.27 +/-0.03. (C) 1999 American Institute of Physics. [S1063-7 834(99)02905-6].