Germanium is a promising candidate for potential channel materials due to its higher hole and electron mobility. To minimize the oxide-semiconductor interfacial defect density, a proper passivation layer must be used before the oxide layer is deposited. In this study, a monolayer of H2O chemisorbates is shown to activate TMA chemisorption due to the Ge-OH bonds catalyzing the formation of an ultrathin passivation layer which can serve as an ideal ALD nucleation template on a Ge surface. However, since H2O chemisorption results in equal density of Ge-H and Ge-OH sites on the Ge(100), H2O can only provide a maximum of 0.5 monolayer of Ge–OH sites, limiting the TMA nucleation density. By using H2O2 dosing, the density of Ge–OH sites can be doubled thereby increasing the potential TMA nucleation density. This study compares the passivation of the Ge(100) surface via H2O and H2O2, for the application of nucleating ALD growth on the surface, using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS).

A saturation H2O dose onto Ge(100) resulted in 0.85 ML coverage of –OH and –H species chemisorbed on the surface. The remaining unreacted atoms on the surface have half filled dangling bond states causing a large local amount of conduction band edge states in the bandgap. The Ge–OH and Ge–H sites on the surface have limited thermal stability. Annealing the H2O/Ge(100) sample to 100°C significantly reduces the H2O coverage due to the recombinative desorption of H2 or H2O.

A saturation dose of H2O2 on Ge(100) at 25oC results in a coverage of 0.95 ML of Ge–OH species chemisorbed on the surface with very few unreacted sites. Compared to a H2O dose, H2O2 provides more than double the number of reactive Ge-OH sites thereby increasing the number of potential ALD nucleation sites. In contrast to the H2O passivated surface, annealing the H2O2/Ge surface to 100°C generates no additional dangling bond sites and even eliminates the dangling bonds present from the 25oC dose and forms a highly ordered surface of Ge-OH bonds. The improved coverage of Ge–OH sites allows for increased nucleation density of O-Al bonds and also minimizes the dangling bonds which are considered as the major source of interfacial trap states (Dit). The improved thermal stability allows for an increased thermal budget during ALD cycles. STS measurements show that TMA nucleation on the H2O2 functionalized Ge(100) surface unpins the Fermi level and has a wide bandgap with no band edge states demonstrating very good interface quality.