Effect of H2O chemisorption on passivation of Ge(100) surface studied by scanning tunneling microscopy

The electronic passivation of a Ge(100) surface, via the chemisorption of H2O at room temperature (RT), and the temperature dependence of H2O coverage were investigated using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). With a saturation H2O dose at RT, a highly-ordered structure, due to the dissociative chemisorption of H2O, was observed on a Ge(100) surface with a coverage of 0.85 monolayers (ML). Annealing the room temperature H2O-dosed Ge surface to 175 °C decreased the coverage of H2O to 0.6 ML. Further annealing at 250 °C decreased the coverage of H2O sites to 0.15 ML, and the surface reconstruction of Ge dimers was observed over much of the surface. Annealing above 300 °C induced Ge suboxide structures, similar to the oxygen-dosed Ge surface. STS measurements confirmed that the surface dangling bond states near Fermi energy are removed by the H2O chemisorption because the dangling bonds of Ge atoms are terminated by ―OH and ―H. The H2O pre-dose at room temperature provides a template for the ultrathin passivation of Ge(100) surface via atomic layer deposition (ALD) at RT, since near monolayer nucleation can be obtained with a 1/2 hydroxylated and 1/2 hydrogenated Ge surface.