ANODIC OXIDES ON SILICON

The formation of anodic oxides on n- and p-type silicon is investigated by chronoamperometry, in situ ellipsometry, in situ excess microwave reflectivity measurements, ex situ X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) and low energy electron diffraction (LEED). Comparison with data on thermally oxidized samples reveals that anodic oxides are less dense being characterized by a composition profile. In addition differences in the etching rate and composition profile of anodic oxides on n-Si and p-Si are observed. The microwave measurements allow a correlation between oxide formation in NH4F solution and changes in charge transfer velocity and surface recombination velocity. At high anodic potentials, photocurrent oscillations on oxidized samples occur at oxide coverages of about 35-40 angstrom as evidenced by XPS. The surface conditions during dark current flow are investigated by XPS, UPS and LEED. The dark current is associated with distinct surface changes resulting in an electrolytically hydrogenated surface if samples are emersed after the dark current decay. Photocurrent multiplication processes are briefly described, studied by intensity modulated photocurrent spectroscopy (IMPS).