Transient capacitance measurements of hole emission from interface states in MOS structures

Abstract

The energy spectrum of MOS interface states and the capture cross section for holes have been measured in p-type silicon by transient capacitance spectroscopy. In MOS capacitors with interface state densities of <1010 cm−2 eV−1 near midgap, the density decreases with energy towards the valence-band edge over the measurement range of 0.17 <E−Ev<0.6 eV. The capture cross section for holes is of the order of 5×10−13 cm2 and is independent of temperature and energy. It appears that the measured distribution consists of acceptor states that extend from the conduction band into the lower half of the silicon forbidden band. The absence of a detectable signal from interface states in a valence-band tail implies that the capacitance transient for hole emission is outside the measurement range. A sharply peaked signal observed for electron (minority carrier) capture at high temperatures indicates that these states are present, but have an extremely low capture cross section for holes, ⩽10−23 cm2.