J. Phys. IV France 125 (2005) 565-567
DOI: 10.1051/jp4:2005125130

Space charge layer dynamics at oxide-semiconductor interfaces under optical modulation: Theory and experimental studies by non-contact photocarrier radiometry

A. Mandelis^{1, 2}, J. Batista¹, M. Pawlak^{2, 3}, J. Gibkes² and J. Pelzl<sup>2

1</sup>  Center for Advanced Diffusion-Wave Technologies (CADIFT), Dept. of Mechanical and Industrial Engineering, Univ. of Toronto, 5 King's College Road, Toronto, Ontario, M5S 3G8, Canada
²  Institut fuer Experimentalphysik III, Festkoerperspekroskopie, Ruhr-Universitaet Bochum, 44801 Bochum, Germany
³  Institute of Physics, Nicolaus Copernicus University, Torun, Poland

Abstract
The dynamic theory of the optically modulated space charge layer (SCL) resulting from band-bending at a Si - SiO₂ interface was developed in terms of the density of interface charges occupying bandgap energy states. Expressions were derived for these interface charge densities, interacting with the free carrier-density-wave generated in the SCL and in the quasi-neutral region (bulk) by an intensity-modulated super-bandgap laser. The PCR theory incorporating these effects was further developed. It was found to involve the dc, fundamental, and entire harmonic spectrum of the excitation frequency as a result of the optical modulation of the curvature of the energy bands and the SCL width at the interface. PCR was used experimentally with a harmonically modulated low-power laser pump and a superposed dc super-bandgap optical bias (a secondary laser beam) to control and monitor the space-charge-layer width in oxidized p-Si - SiO₂ and n-Si - SiO₂ interfaces (wafers) exhibiting charged interface-state related band-bending. The application of the theory to the experiments yielded the various transport parameters of the samples as well as depth profiles of the SCL exhibiting complete (p-type Si) or partial (n-type Si) band-flattening, to a degree controlled by the widely different minority carrier capture cross-section at each interface. The uncompensated charge density at the interface was also calculated from the theory.

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