Reactor design considerations are discussed relevant to the two main problems, carbon contamination and low growth rate, facing Atomic Layer Epitaxy (ALE) of GaAs. A new reactor design addressing these problems is described. It utilizes the concept of rotating the substrate between streams of reactant gases. The growth chamber provides baffles and gas jets to shear off and sweep away the thermal boundary layer after exposure to the reactive gas streams. Construction is based on modification of a commercially available low pressure MOCVD reactor equipped with a. load lock. The reactor is capable of processing three, two-inch wafers. A background carbon concentration of about 1015cm−3 and a 77°K mobility of 30,000 cm2/V-sec were achieved. Self limited growth was observed for a growth temperature as high as 600 °C. Controlled p- and n-type doping was accomplished by changing growth conditions and adding silane.