Minority carrier annihilation at crystalline silicon surface in MOS structure

Photo-induced minority carrier annihilation properties at the silicon surface in metal-oxide-semiconductor (MOS) structure were reported using a 9.35 GHz microwave transmittance measurement. Al electrodes were formed with a size of 0.1 × 2.0 cm² at the top surface and with a half area at the rear surface of 12-Ωcm-n-type 500-μm-thick crystalline silicon substrates coated with 100-nm-thick thermally grown SiO₂ layers. The bias voltage was applied to the Al electrode at the top surface. We observed microwave absorption by photo-induced carriers laterally diffusing into the silicon region placed in the microwaveguide tube through the region coated with the Al electrode from 635 nm light illumination region outside of the waveguide tube. The microwave absorption resulted in that the carrier recombination defect density at the top silicon surface increased from 2.3×10¹⁰ to 4.8×10¹⁰ cm^-2 as the bias voltage decreased from 0 to -2.0 V.