Suppression of boron segregation by interface Ge atoms at SiGe/SiO2 interface

We investigate the migration pathway and barrier for B diffusion at SiGe/SiO2 interface through first-principles density functional calculations. Similar to the diffusion mechanism reported for Si/SiO2 interface, a substitutional B, which initially forms a B-self-interstitial complex in SiGe, diffuses to the interface and then to the oxide in form of an interstitial B. At the defect-free interface, where bridging O atoms are inserted to remove interface dangling bonds, it is energetically more favorable for the interstitial B to intervene in the Ge–O bridge bond rather than the Si–O bridge bond at the interface. As a result of the B intervention, interface Ge atoms significantly enhance the stability of B-related defects in the interface region and thereby act as traps for B dopants. At the interface with the Ge–O bridge bond, the overall migration barrier for B diffusion from SiGe to SiO2 is estimated to be about 3.7 eV, much higher than the reported value of about 2.1 eV at Si/SiO2 interface. Our results provide a clue to understanding the experimental observation that B segregation toward the oxide is suppressed in SiGe/SiO2 interface.