Determination of the MOS flatband condition by electroreflectance and capacitance measurements

Different flatband voltage values are obtained, depending on whether these are determined from electroreflectance (ER) or differential capacitance (CV) measurements. This difference is attributable to inhomogeneities in semiconductor doping. An accumulation or depletion of ionized doping atoms in the semiconductor interface zone causes the interface charge Qs to shift the capacitance voltage curve toward higher or lower gate voltages. A model of deep impurity doping in the semiconductor interface is presented which explains the voltage difference and yields two parameters: (i) the deep impurity concentration in the semiconductor interface zone (Qs ≈︁ 2 × 1011 cm−2, and (ii) the lower limit of the doping depth of the deep impurities (Ld > 3 nm).