Effect of Ba termination layer on chemical and electrical passivation of Ge (1 0 0) surfaces

During the deposition process of high-k gate oxides on Ge, the Ge interface tends to be oxidized to form GeOx, leading to the introduction of interface states which compromise transistor performance. It has been suggested that a Ba termination layer on Ge could fulfill the same passivating role on Ge as reported for Sr on Si. In this paper, we present LEED, UPS and XPS studies on the effect of Ba overlayers on the chemical and electrical passivation of Ge(1 0 0). For 1 ML coverage, the adsorbate phase has (1×1) symmetry, as observed by LEED. Ba is seen to significantly increase the oxidation tendency of the Ge(1 0 0) surface. Using UPS, 1 ML Ba was seen to reduce surface band bending by 200 meV on n-type Ge, suggesting that Ba deposition causes transfer of electrons to the Ge substrate, resulting in a surface dipole. The role of this dipole in oxidation enhancement and possible electronic passivation effects is discussed.