N-doped graphene-like coating for improved microcapacitance of nanoporous silicon

Silicon wafers are the main platform for the integrating of electronic devices, porous silicon (pSi) is a promising material for on-chip microcapacitor electrodes. A method is proposed to improve the electrochemical efficiency of pSi by depositing a nitrogen-doped graphene-like coating (N-GLC) on it. N-GLC is first used to coat the entire 80 μm pSi layer. The sharp pressure drops during chemical vapor deposition (CVD) of N-GLC allow N-doped carbon to be deposited throughout the full depth of the pores. Graphitic N (the main configuration of nitrogen in N-GLC) enhances the conductivity of the composite. Moreover, the influence of GLC penetration depth in pSi on its capacitance is investigated.

Electrochemical impedance spectra, cyclic voltammetry, and galvanostatic charge-discharge data in 3M H₂SO₄ are presented along with the results of cyclic stability measurements. High capacitance (145 mF/cm²) and excellent cyclic stability (over 20,000 cycles even at low scan rates) are achieved for a pSi microcapacitor electrode. Considerably higher values have been reported only in ionic electrolytes and/or with an additional MnO_x coating on silicon nanowires – morphologically similar materials that require complicated technology.