Abstract: In the fabrication of double heterostructure GaAsAlGaAs junction lasers by molecular beam epitaxy, it has been found that suitably annealing the entire heterostructure increases the external quantum efficiency of the laser and reduces the room temperature threshold for lasing. Also described is a technique using relatively uncollimated beams to deposit continuously on the interior walls of the vacuum chamber fresh layers which getter deleterious contaminants. In addition, pyrolytic boron nitride, rather than graphite, effusion cells are utilized in order to reduce the amount of CO formation in the system.