Energetics of Si(001) Surfaces Exposed to Electric Fields and Charge Injection

We perform density-functional calculations on the influence of external electric fields and electrons or holes injected into surface states on the relative stability of c(4×2) and p(2×2) reconstructed Si(001) surfaces. It is shown that an electric field parallel to the $[001]$ direction or the insertion of electrons into surface states favors the formation of p(2×2) periodicities. Our results explain recent experimental studies reporting changes of surface reconstruction of Si and Ge(001) surfaces induced by the scanning tunneling microscope and the occurrence of p(2×2) reconstructions on $(001)$ surfaces of n-doped Si.