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-alky
l bonds of the form Si-CnH2n+1 (n greater than or equal to 1). The electric
al 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 w
ith aqueous acids is < 20 cm s(-1), this surface deteriorates within 30 min
in an air ambient, yielding a high surface recombination velocity. In cont
rast, methylated Si(111) surfaces exhibit low surface recombination velocit
ies in air for more than 4 weeks. Low surface recombination velocities were
also observed for Si surfaces that had been modified with longer alkyl cha
ins. (C) 2000 American Institute of Physics. [S0003-6951(00)01739-3].