THE INFLUENCE OF SURFACE-STATES ON THE PHOTOVOLTAGE OF REAL SILICON SURFACES

The surface photovoltage caused by band-to-band generation within the semiconductor depends on light intensity. This dependence differs significantly in two limiting cases. When recombination via fast surface states is negligible, the slope of the photovoltage versus the logarithm of intensity is always less than kT/e and depends on the amount of semiconductor band bending in the dark. When recombination via fast surface states becomes strong, this slope is kT/e, independent of the band bending. These differences are experimentally observed using a structure with ferroelectric NaNO2 deposited on a real silicon surface. The switching of the direction of the spontaneous polarization of the ferroelectric results in significant changes of the semiconductor band bending in the dark. The charge exchange with slow surface states results in a continuous change of the band bending in the dark. The measurements reveal a pronounced minimum of the density of fast surface states near mid-gap. The results compare well to those from measurements on a field effect transistor structure with NaNO2 as gate insulator.