Silicon Surface Passivation by Organic Monolayers: Minority Charge Carrier Lifetime Measurements and Kelvin Probe Investigations

摘要

The silicon surface passivation of monolayers of organic compounds that are bound to Si surfaces by a covalent Si-C bond has been investigated. The effective lifetime τ_(eff) of minority charge carriers in the surface-modified semiconductor has been determined by modulated free carrier absorption (MFCA) measurements. The results show tht on 1-2 Ω·cm p-type Si(100) surfaces modified with a monolayer obtained from CH_2=CH-(CH_2)_8-C(=O)-O-CH_3 maximum effective lifetimes τ_(eff) ≥ 130 μs can be obtained. This value corresponds to a maximum surface recombination velocity S_(eff) of 120 cm/s, a value that is similar to those obtained using other passivation techniques, which demonstrates that these monolayers provide an interesting alternative for silicon surface passivation. During these MFCA measurements an unusual time dependence of the effective lifetime is observed: τ_(eff) rises continuously during illumination of the substrate. Kelvin probe measurements show that there is a slow shift of the Fermi level of the semiconductor under illumination, which seems to be the result of a slow, reversible filling of surface traps.