High sensitivity detection of silicon surface reactions by photoconductance decay

We use radio-frequency photoconductance decay (RFPCD) for irt situ studies of silicon surface reactions. For high bulk lifetime wafers, the measured lifetime depends strongly on surface recombination velocity, Chemisorption of iodine (I-2) from methanol (CH3OH) obeys the Langmuir isotherm with n (order of adsorption reaction) = 0.95 for Si (111) surfaces. Chemisorption of oxygen on HF-passivated silicon increases the density of surface recombination centers (N-T); the barrier height for Si-O bond formation, as estimated from dN(T)/dt, is 1.2 eV, Trace amounts of copper, deposited onto silicon from dilute HF, introduce surface states with energy levels in the Si bandgap. Using total reflection X-ray fluorescence in conjunction with RFPCD, we obtain a cross section for minority carrier capture at surface copper atoms of 8 x 10(-17) cm(2) for electrons and 5 x 10(-17) cm(2) for holes.