Electrical, Photoelectrochemical, and Photoelectron Spectroscopic Investigation of the Interfacial Transport and Energetics of Amorphous TiO_2/Si Heterojunctions

Solid-state electrical, photoelectrochemical, and photoelectron spectroscopic techniques have been used to characterize the behavior and electronic structure of interfaces between n-Si, n^+-Si, or p^+-Si surfaces and amorphous coatings of TiO_2 formed using atomic-layer deposition. Photoelectrochemical measurements of n-Si/TiO_2/Ni interfaces in contact with a series of one-electron, electrochemically reversible redox systems indicated that the n-Si/TiO_2/Ni structure acted as a buried junction whose photovoltage was independent of the formal potential of the contacting electrolyte. Solid-state current–voltage analysis indicated that the built-in voltage of the n-Si/TiO_2 heterojunction was ∼0.7 V, with an effective Richardson constant ∼1/100th of the value of typical Si/metal Schottky barriers. X-ray photoelectron spectroscopic data allowed formulation of energy band-diagrams for the n-Si/TiO_2, n^+-Si/TiO_2, and p^+-Si/TiO_2 interfaces. The XPS data were consistent with the rectifying behavior observed for amorphous TiO_2 interfaces with n-Si and n^+-Si surfaces and with an ohmic contact at the interface between amorphous TiO_2 and p^+-Si