Investigation of energetic surface state distributions at real surfaces of silicon after treatment with HF and H₂O using large-signal photovoltage pulses

Abstract

It is shown that the field-modulated large-signal photovoltage offers definite methodological advantages in comparison to other methods more frequently used for the determination of surface state distribution. Apparatus and sample preparations are described. The distribution of fast states in the forbidden gap at real silicon surfaces was studied after treatment in HF and rinsing in H2O up to times in excess of 100 h. Whilst for short rinsing times minimum concentrations of 3*1012 states cm-2 eV-1 were found, prolonged rinsing led to an 'intrinsic' distribution where the concentration in the minimum was lower by a factor of ten. The results are compared with those recently obtained at thermally oxidised silicon. A meaningful separation of surface states into three groups of different physical origin is possible both for real and for oxidised silicon surfaces. Fluoridation as a probable cause of extrinsic surface states, model descriptions of intrinsic states and, finally, certain aspects concerning semiconductor device technology are discussed.