Carrier-selective heterojunctions are important for low-cost silicon-based photovoltaic applications. A low temperature (<100 °C) chemical vapor deposition technique is used here to deposit ultrathin (n-type) titanium dioxide (TiO2) layers onto hydrogen-passivated surfaces of crystalline-silicon (c-Si). Energy level alignment and chemical composition at these abrupt, interfacial layer-free TiO2/Si heterojunctions are investigated via ultraviolet, X-ray, and inverse photoemission spectroscopy, for c-Si doping ranging from p++(1019) to n++(1019). The interface Fermi level position and device-relevant TiO2/Si band offsets are found to shift monotonically as a function of the Si doping, revealing the absence of Fermi level pinning at the c-Si interface and pointing to simple Fermi level equilibration as the driving mechanism behind the interface energy level alignment. Electrical transport measurements performed on TiO2/Si-based diodes confirm the energy level alignment yielded by spectroscopic measurements and the hole-blocking properties of the TiO2/Si heterojunction, exclude hole conduction in the TiO2 as a transport mechanism, and show carrier recombination at the TiO2/p-Si heterojunction.
All Science Journal Classification (ASJC) codes
- Mechanics of Materials
- Mechanical Engineering
- Fermi level unpinning
- carrier-selective heterojunction
- titanium dioxide