Consideration of doping profiles in MOSFET mobility modeling

The channel mobility of a MOSFET in the strongly inverted, linear regime is an important parameter in this modeling process and depends on the effective normal electric field. It is shown that the general form of this field is E_eff=(ηQ_c+ζQ_b )ε_Si, where Q_c and Q _b are the inversion- and bulk-charge areal densities, respectively, and the coefficient η and ζ determine the weighting of those charge densities. A recent study of p-channel MOSFET transistors indicates that η≈1/3 and ζ=1, which implies that the inversion charge contribution is different for electrons and holes in MOSFETs. It is shown theoretically, by quantum mechanical arguments, that ζ=1/2 for both n- and p-channel MOSFETs and the coefficient of the bulk-charge contribution ζ depends on the doping profile in the near-surface region. A uniform doping profile procedures a value of ζ=1, while a nonuniform profile near the interface leads to ζ>1 (accumulation) or ζ<1 (depletion). Experimental results to support these conclusions are reported