Admittance Spectroscopy of Interface States in Metal/Semiconductor Contacts

Abstract

The identification of interface states at metal/semiconductor (M/SC) contacts have long been key issues in understanding electronic properties of such junctions. Considerable spectroscopic evidence got from studies of a few monolayers deposited on semiconductor surfaces suggests that various effects (chemical formation of a compound, interdiffusion, defects creation…) take place which all can promote localized charge formation /1/. But there is also an interest for thicker layers both because they are really used in technological domains and electrical characterizations can easily apply. A useful tool which allows the detection of charges localized near the interface appears to be capacitance and conductance measurements. If an external force like illumination, electron beam or, like here, voltage difference is applied to the samples, variation of the population of carriers trapped within interface states can take place. This charge variation involves a capacitance and also a conductance (or dielectric losses) because a new steady-state is reached only after some delay corresponding to the time constant of the processes for carriers exchanges between interface states and carrier reservoirs. These phenomena will be analyzed in Section 2 taking the discrete monovalent trap at M/SC interface as a basic example. A brief review of experimental methods will be given in Section 3 and some illustrative results will be shown. Finally, a more detailed theory will be outlined in Section 4 for describing how the interface states density controls capacitance and conductance of a M/SC diode.