Preparation of air-stable, low recombination velocity Si(111) surfaces through alkyl termination

A two-step, chlorination/alkylation procedure has been used to convert the surface Si–H bonds on NH4F(aq)-etched (111)-oriented Si wafers into Si–alkyl bonds of the form Si–CnH2n+1 (n⩾1). The electrical properties of such functionalized surfaces were investigated under high-level and low-level injection conditions using a contactless rf apparatus. The charge carrier recombination velocities of the alkylated surfaces were <25 cm s−1 under high-level and low-level injection conditions, implying residual surface trap densities of <3×109 cm−2. Although the carrier recombination velocity of hydrogen-terminated Si(111) surfaces in contact with aqueous acids is <20 cm s−1, this surface deteriorates within 30 min in an air ambient, yielding a high surface recombination velocity. In contrast, methylated Si(111) surfaces exhibit low surface recombination velocities in air for more than 4 weeks. Low surface recombination velocities were also observed for Si surfaces that had been modified with longer alkyl chains.