Microwave photoelectrochemical studies of silicon interfaces covered with platinum dots

Abstract

n-Type Si electrodes either dotted with Pt particles (5–10 nm) or uncoated, in contact with a propylene carbonate electrolyte solution containing the redox couple ferrocene/ferrocenium, have been investigated with time-resolved microwave conductivity (TRMC) and with potential-dependent stationary-microwave reflection measurements. The impact of the penetration depth of the exciting light on the photoinduced microwave reflection and photocurrent signals for the plain Si/electrolyte interface was examined. In addition the effect of changing the concentration of the redox couple in both systems was compared with the impact of Pt-particle treatment on the Si surface. Two electrochemical waves were observed during the oxidation of ferrocene, the second coinciding with an electrochemically induced decrease of surface recombination at the Si/electrolyte interface. This generates a tail-back in the flow of charge carriers and an increased concentration of minority carriers, visible in the microwave reflection signal. In the presence of Pt dots the increase of the first photocurrent wave is negatively shifted (increased open circuit voltage), whereas the tail-back is positively displaced by 100–200 mV. Simultaneously, a decreased surface recombination is indicated by a larger amplitude of the microwave signal. This results in an increased photocurrent density, provided that transport through the electrolyte is not rate limiting. The main effect of Pt treatment is the improved passivation of the semiconductor electrolyte interface under maintenance of an efficient collection of photogenerated charge carriers via the Pt particles.