First-principles investigation of Sn1−xSix/Si(1 1 1) and Sn1−xPbx/Si(1 1 1) surfaces

We investigate the structural and electronic properties of the Si(1 1 1) surface covered by 1/3 monolayer Sn(1−x)Six as a function of x, by means of density functional theory–local density approximation calculations. Starting from the ideal α-phase Sn/Si(1 1 1), we perform computational experiments increasing the amount of substitutional Si on the adatom layer, a condition which is experimentally achieved through annealing. We find the occurrence of a metal–semiconducting phase transition found at 50% Si composition, related to band decoupling. The role of surface disorder is addressed comparing the theoretical predictions with the experimental results. Finally, we further extend our investigation considering other possible surface alloying, i.e. the Sn(1−x)Pbx/Si(1 1 1) surface.