  The effects of low temperature illumination and annealing on fractional
quantum Hall (FQH) characteristics of a GaAs/AlGaAs quantum well are
investigated. Illumination alone, below 1 K, decreases the density of the 2DEG
electrons by more than an order of magnitude and resets the sample to a
repeatable initial state. Subsequent thermal annealing at a few Kelvin restores
the original density and dramatically improves FQH characteristics. A reliable
illumination and annealing recipe is developed that yields an energy gap of 600
mK for the 5/2 state.
