Enhanced Ge/Si(001) island areal density and self-organization due to P predeposition

The predeposition of P, with coverages theta(P) ranging from 0 to 1 ML, on Si(001) significantly increases both the areal density and spatial self-organization of Ge islands grown by gas-source molecular beam epitaxy from hydride precursors. The Ge island density rho(Ge) initially increases with theta(P), reaching a maximum of 1.4 x 10(10) cm(-2) at theta(P) = 0.7 ML, a factor of four times higher than on bare Si(001) under the same deposition conditions, before decreasing at higher P coverages. The increase in rho(Ge)(theta(P)) is due to a corresponding decrease in Ge adatom mean free paths resulting from passivation of surface dangling bonds by adsorbed pentavalent P atoms which, in addition, leads to surface roughening and, therefore, higher Ge coverages at constant Ge2H6 dose. As theta(P) (and hence, rho(Ge)) increases, so does the degree of Ge island ordering along < 100 > directions due to the anisotropic strain field surrounding individual islands. Similar results are obtained for Ge island growth on P doped Si(001) layers where strong P surface segregation provides partial monolayer coverage prior to Ge deposition. (C) 2011 American Institute of Physics. [doi:10.1063/1.3587226]