Near-surface channel impedance measurements, open-circuit impedance spectra, and differential capacitance vs potential measurements of the Fermi level position at Si/CH3CN contacts

Near-surface channel impedance measurements, open-circuit impedance spectra, and differential capacitance vs potential measurements have been used to determine the barrier height of liquid contacts formed with n-type and p-type Si electrodes. Barrier heights were measured as the redox potential, E(A/A(-)), of a metallocene-based, one-electron, outer-sphere, acceptor/donor (A/A(-)) pair was varied in CH3CN solvent. The barrier heights of p-Si(111) electrodes in contact with CH3CN-Me(10)Fc(+/0) (where Me(10)Fc is decamethylferrocene) or CH3CN-CoCp2+/0 (where CoCp2 is cobaltocene) were 0.69 +/- 0.1 and 1.1 +/- 0.1 V respectively. In contrast, barrier heights for n-Si(111)/CH3CN-Me(10)Fc(+/0) and n-Si(111)/CH3CN-CoCp2+/0 contacts were 0.66 +/- 0.1 and 0.09 +/- 0.01 V, respectively. These measurements indicate that the barrier heights closely track changes in the electrochemical potential of the contact, instead of being relatively invariant to changes in the Fermi level of the contacting phase, as is observed for Si/metal Schottky barriers. These measurements also demonstrate that the low effective surface recombination velocity, S, for silicon in contact with CoCp2+/0 is primarily the result of an accumulation layer rather than solely being due to a low density of surface electrical defects.