Minority Carrier Annihilation at Crystalline Silicon Interface in Metal Oxide Semiconductor Structure
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Minority Carrier Annihilation at Crystalline Silicon Interface in Metal Oxide Semiconductor Structure Jun Furukawa1, Satoshi Shigeno1, Shinya Yoshidomi1, Tomohito Node1, Masahiko Hasumi1, Toshiyuki Sameshima1, and Tomohisa Mizuno2 1 Tokyo University of Agriculture and Technology, Tokyo, 184-8588 Japan 2 Kanagawa University, Kanagawa, 259-1293 Japan ABSTRACT We report photo induced minority carrier annihilation at the silicon surface in a metal–oxide– semiconductor (MOS) structure using 9.35 GHz microwave transmittance measurement. 7 cm n-type 500-μm-thick crystalline silicon substrate coated with 100-nm-thick thermally grown SiO2 layers was used. 0.2-cm-long Al electrode bars were formed at the top and rear surfaces. 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. Microwave transmittance system detected photo induced carriers diffused from the light illuminated region via the MOS structured region. When the bias voltage was applied at +2.0 and -2.2 V to the electrode at the top surface, the surface recombination velocity increased from 44 (initial) to 83 and 86 cm/s, respectively because of depletion region formation at rear and top surface respectively. Those voltage applications caused change in the distribution of photo induced carriers in a 0.6-cm-wide region including light illuminated, MOS structured, microwave irradiated regions.
INTRODUCTION A long carrier lifetime with a low density of defect states is required for fabrication of high performance devices such as photo sensors, solar cells and metal-oxide-semiconductor (MOS) field effect transistors [1-3]. Carrier recombination defect states seriously affect the minority carrier effective lifetime of silicon [4,5] and mainly concentrate at the silicon surface or its interface. In the case of MOS structure, the application of a bias voltage onto metal electrodes causes band bending and changes in the carrier concentration of the silicon surface region that satisfy the charge neutrality between both sides of the oxide insulating layer. Because the bias voltage changes the occupation probability of surface defect states, the photo induced carrier recombination probability depends on the bias voltage. The direct measurement of photo induced carrier recombination probability as a function of bias voltage will give useful information for fabricating high performance photo sensors and passivation layers for photovoltaic devices. Recently, we reported the measurement of the light induced excess carrier recombination velocity at the silicon surface in the MOS structure using a 9.35 GHz microwave transmittance measurement system with continuous wave (CW) light illumination [6,7]. We demonstrated a change in the microwave absorption of photo induced carriers laterally diffused in the silicon region of the MOS structure with the application of bias voltage. The bias voltage application causes a change in the carrier recombination probability. In this paper, we report precise anal
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