Schottky barrier tuning with heterovalent interlayers: Al/Ge/GaAs versus Al/Si/GaAs

Using ab initio calculations, we compare the effects produced on the Al/GaA s(100) Schottky barrier height by Ge and Si interface layers with thickness ranging from 0 to 2 monolayers. The dipole layers, generated by the group- IV atomic substitutions at the interface, increase/decrease the p-type Scho ttky barrier at the As-/Ga-terminated Al/GaAs(100) junction. Although the t rends with Ge and Si interlayers are similar for coverages less than 0.5 mo nolayers, at higher coverages the Schottky barrier exhibits a stronger nonl inear behavior, and smaller barrier variations, in Al/Ge/GaAs(100) than in Al/Si/GaAs(100). In particular, at a coverage of 2 monolayers, the use of G e interlayers instead of Si ones reduces by 25% the barrier tunability. The se trends are at variance with those predicted by existing macroscopic band -structure models, and our results should help in discriminating between di fferent mechanisms of Schottky barrier tuning. (C) 2000 American Vacuum Soc iety. [S0734-211X(00)00204-3].