The Impact of Different Si Surface Terminations in the (100) p-Si | n+-Si | Cu Junction with Respect to the Photo Electrochemical Performance

The (100) p-Si vertical bar n(+)-Si vertical bar Cu interface is investigated with respect to the electronic band structure and the electrochemical performance. Thin layers of metallic copper were deposited stepwise by E-beam deposition and analyzed in-line by XPS after each deposition step. For this purpose, different silicon surface terminations were prepared: hydrogen termination, thermal oxide (7 angstrom) and native oxide (3 angstrom). After contact formation the initial flatband situation of the n(+)-Si layer changes to an upward band bending depending on the Si surface termination: 0.45 eV for the H termination, 0.35 eV for the native oxide and 0.27 eV for the thermal oxide. The electrochemical performance measured by cyclic voltammetry for each junction correlates to the respective energy band alignment. While the H terminated surface with the highest upward band bending leads to the worst electrochemical performance, the surface passivated with thermal oxide and the lowest upward band bending results in the best electrochemical performance. For the two passivated surfaces, the thickness of the passivating oxide layer may also be an issue. The Si surface with a thicker thermal oxide (7 angstrom) shows better band alignment and electrochemical performance compared to the Si surface with a thinner native oxide (3 angstrom). (C) The Author(s) 2019. Published by ECS.