ARSENIC SURFACE SEGREGATION AND INCORPORATION IN SI AND SI1-XGEX DURING GAS-SOURCE MOLECULAR-BEAM EPITAXY

The surface segregation of As in Si and Si1-xGex during gas source mol ecular beam epitaxy (GSMBE) has been investigated. It is shown that th e segregation process is suppressed in the alloy compared with pure Si . The segregation energy is shown to be dependent on growth temperatur e and has been attributed to a change of surface hydrogen coverage. Su rface hydrogen blocks surface sites, thus acting as a surfactant to su ppress As segregation. Arsenic incorporation from AsH3 involves dissoc iative chemisorption via empty surface sites. The balance between the rate of dissociation, surface segregation and desorption results in a temperature and Ge concentration dependence of the net effective flux of As and consequently its concentration in the film. It has an upper limit of less than 10(18) cm(-3) in Si, but much higher concentrations can be achieved in Sice alloys.