 next depositing sufficient atoms of As to combine with {HEAD ~ the Al and Ga monolayers} to form AlAs and {TAIL ~ GaAs monolayers}; and, 
to form
next depositing sufficient atoms of As to combine with { HEAD ~ the Al and Ga monolayers } to form AlAs and { TAIL ~ GaAs monolayers } ; and ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH