Optically active interface states in MOS structures

Abstract

The results of studies of the interface states in clean n-type MOS capacitors by the low-temperature photocapacitance technique are reported. Energy distribution of the interface states density and photoionization cross-section are determined from the analysis of the photocapacitance kinetic. It is shown that the energy distribution of the interface state density can be described by the Gaussian distribution with maximum at about 0.7 eV below the conduction band edge and standard deviation of about 0.1 eV. The photoionization cross-section of these states can be described by the Lucovsky relationship. The maximum of the photoionization cross-section vs photon energy was equal to about 5 × 10 −20/( E c − E ss ) cm 2 for a given energy of the interface states E ss . From the comparison of the photocapacitance and quasi-static C-V measurements the existence of two types of interface states is suggested: “optically active states” with density decreasing towards the band edges, and “optically inactive states” with density increasing towards the band edges. No photocapacitance associated with “optically inactive states” was observed.