  We have observed the Zeeman-split excited state of a spin-1/2 multi-electron
Si/SiGe depletion quantum dot and measured its spin relaxation time T1 in
magnetic fields up to 2 T. Using a new step-and-reach technique, we have
experimentally verified the g-value of 2.0 +/- 0.1 for the observed Zeeman
doublet. We have also measured T1 of single- and multi-electron spins in InGaAs
quantum dots. The lifetimes of the Si/SiGe system are appreciably longer than
those for InGaAs dots for comparable magnetic field strengths, but both
approach one second at sufficiently low fields (< 1 T for Si, and < 0.2 T for
InGaAs).
