Arsenic surface segregation and incorporation in Si and Si1-xGex during gas source molecular beam epitaxy

Abstract

The surface segregation of As in Si and Si1-xGex during gas source molecular beam epitaxy (GSMBE) has been investigated. It is shown that the segregation process is suppressed in the alloy compared with pure Si. The segregation energy is shown to be dependent on growth temperature and has been attributed to a change of surface hydrogen coverage. Surface hydrogen blocks surface sites, thus acting as a surfactant to suppress As segregation. Arsenic incorporation from AsH3 involves dissociative 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 1018 cm-3 in Si, but much higher concentrations can be achieved in SiGe alloys.