Dielectric properties of single crystalline PrO_2(111)/Si(111)heterostructures: Amorphous interface and electrical instabilities

摘要

Single crystalline PrO_2(111)/Si(111) heterostructures are flexible buffers for global Ge integration on Si. A combined materials science-electrical characterization is carried out to study the influence of postdeposition annealing in 1 bar oxygen at 300-600 ℃ on the dielectric properties of PrO_2(111)/Si(111). The materials science transmission electron microscopy and x-ray reflectometry studies reveal that postdeposition oxidation of the PrO_2(111)/Si(111) boundary results in an amorphous interface (IF) layer, which grows in thickness with temperature. Nondestructive depth profiling synchrotron radiation-based x-ray photoelectron spectroscopy and x-ray absorption spectroscopy methods demonstrate that this amorphous IF layer is composed of two Pr-silicate phases, namely, with increasing distance from Si, a SiO_2-rich and a SiO_2-poor Pr silicate. The electronic band offset diagram shows that the wide band gap dielectric Pr silicate results in higher band offsets with respect to Si than the medium band gap dielectric PrO_2. The electrical characterization studies by C-V measurements show that (a) well-behaved dielectric properties of the PrO_2(111)/IF/Si(111) are achieved in a narrow postdeposition oxidation window of 400-450 ℃ and that (b) defects are distributed over the Pr-silicate IF layer. Temperature-dependent J-V studies report furthermore that the formation of the single crystalline PrO_2/amorphous Pr-silicate bilayer structure on Si(111) results in (a) improved insulating properties and (b) strong electrical instability phenomena in the form of a Maxwell-Wagner instability and dielectric relaxation.