Time-resolved Kerr reflectivity of two-dimensional electron gases in I
l-VI semiconductors provides a direct measure of electron spin precess
ion and relaxation over a temperature range from 4 to 300 kelvin. The
introduction of n-type dopants increases the electronic spin lifetimes
several orders of magnitude relative to insulating counterparts, a tr
end that is also observed in doped bulk semiconductors. Because the el
ectronic spin polarization in these systems survives for nanoseconds,
far longer than the electron-hole recombination lifetime, this techniq
ue reveals thousands of spin precession cycles of 15 gigahertz per tes
la within an electron gas. Remarkably, these spin beats are only weakl
y temperature dependent and persist to room temperature.