Photo induced minority carrier annihilation at crystalline silicon surface in metal oxide semiconductor structure

Abstract

We report the properties of features of photo induced minority carrier annihilation at the silicon surface in a metal–oxide–semiconductor (MOS) structure using 9.35 GHz microwave transmittance measurement. 7 Ω cm n-type 500-µm-thick crystalline silicon substrates coated with 100-nm-thick thermally grown SiO2 layers were prepared. Part of the SiO2 at the rear surface was removed. Al electrode bars were formed at the top and rear surfaces to form the structures Al/SiO2/Si/SiO2/Al and Al/SiO2/Si/Al. 635 nm light illumination onto the top surface caused photo induced carriers to be in one side of the silicon region of the Al electrode bar of the structure Al/SiO2/Si/SiO2/Al. Microwave transmittance was measured on the other side of the silicon region of the Al electrode bars. The measurement and analysis of microwave absorption by photo induced carriers laterally diffusing across the silicon region coated with Al electrodes revealed a change in the carrier recombination velocity at the silicon surface with the bias voltage applied onto the top Al electrode. The applied bias voltages of +2.0 and −2.2 V gave peaks at surface recombination velocities of 83 and 86 cm/s, respectively, for the sample structure Al/SiO2/Si/SiO2/Al, while it was 44 cm/s under the bias-free condition. A peak surface recombination velocity of 81 cm/s was only observed at a bias voltage of −2.0 V for the sample structure Al/SiO2/Si/Al.