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 greater than or equal to 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 < 3x10(9) 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. (C) 2000 American Institute of Physics. [S0003-6951(00)01739-3].