Multiple quantum wells (MQWs) have been grown at low substrate temperatures by molecular beam epitaxy so as to incorporate excess arsenic. This excess arsenic precipitates and preferentially coarsens to the lower band gap well regions with anneal. Despite the excess arsenic, these AlAs/GaAs MQW structures exhibit sharp excitonic features that are comparable to those exhibited by stoichiometric MQW structures grown at standard temperatures. In addition to the sharp excitonic transitions, these MQWs possess ultrafast recombination lifetimes making them attractive for photorefractive, electro-optic sampling, and saturable absorption applications.