Gallium Evaporation Behavior for Purification in Molecular Beam Epitaxy

High mobility GaAs/AlGaAs heterostructure have been achieved at Purdue University through in-situ distillation of the source Ga prior to growth. A significant amount of Ga is lost during distillation and growth. To evaluate the Ga behavior during MBE operation, the evaporation rate from a planar source of liquid Ga in a crucible is analyzed, correcting for transmission probability according to Clausing theory. The transmission probability which depends on the diameter and receding depth of the liquid surface in the crucible, explains condensation of Ga particles by collision for the vertically standing crucible. The good agreement furthermore suggests that the usual tilt of the cell has little effect on the flux.