Cyclic Voltammetry Peaks Due to Deep Level Traps in Si Nanowire Array Electrodes

When metal-assisted chemical etching (MACE) is used to increase the effective surface area of Si electrodes for electrochemical capacitors, it is often found that the cyclic voltammetry characteristics contain anodic and cathodic peaks. We link these peaks to the charging-discharging dynamics of deep level traps within the nanowire system. The trap levels are associated with the use of Ag in the MACE process that can leave minute amounts of Ag residue within the nanowire system to interact with the H ₂ O layer surrounding the nanowires in a room temperature ionic liquid. The influence of the traps can be removed by shifting the Fermi level away from the trap levels via spin-on doping. These results in lower capacitance values but improved charge-discharge cycling behavior. Low-frequency noise measurements proof the presence or absence of these deep level traps.