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