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It is shown that, because of the electrostriction and polarization of defects by the modulating electric field, electroreflectance spectra are more affected by defects than are third-derivative spectra from ellipsometry data. The theory of electroreflectance is generalized to include these effects. Plasticity and long-range strains are shown to lead to a first-derivative line shape and polarizable defects to a second-derivative line shape. For defect-rich samples these new terms dominate the usual third-derivative line shape. PACS numbers: 78.20.Jq, 71.55.Fr Low-field electrolyte electrorefiectance (EER) has been used primarily to determine accurately the interband transition energies, E,, in semiconductors. According to the existing theory' the EER spectrum is proportional to a linear combination of the third derivatives of the real and imaginary parts, e) and e2, of the complex dielectric function, e(E), with respect to energy. This third-derivative expression leads to an approximate parameterized functional form, the third-derivative functional form (TDFF), which fits remarkably well the EER spectra obtained from defect-free semiconducting surfaces. The fits yield values for the critical energy E,, the linewidth I,, and the phase 0, associated with the Ith transition. Because e~(E) and e2(E) can be measured by automatic spectroscopic ellipsometry (ASE), it is also possible to compute numerically from the independently measured ASE data the third-derivative line shape (TDL) which, according to this theory, should be proportional to the EER line shape.However, our EER data for mercury cadmium telluride (Hgt "Cd"Te) cannot be well fitted by the TDFF and are in serious disagreement with the TDLs obtained from ASE data. In particular, we have studied the effects of different surface treatments on EER spectra4 5 and have reported4 that chemical or chemomechanical treatment of the surface of Hg~"Cd"Te samples substantially changes the linewidth and overall shape of their EER spectra. In contrast, Arwin, Aspnes, and Righer have recently presented ASE results which show that similar surface treatments performed on comparable samples do not measurably affect the linewidth of the TDL. This contrast between EER and ASE results led us to suspect5 the possibility of an interaction between the EER modulating electric field and the defects. This idea was further supported by the failure of the conventional TDFF to fit most Hg~"Cd"Te EER spectra except over a narrow range around each critical-point energy.These results have led us to formulate a new, more general theory of EER which incorporates the effect of defects on the electroreflectance line shape and thus allows us to obtain quantitatively inforrnation about defects in near-surface regions of defectuous semiconductors such as Hg~"Cd"Te. This treatment includes two new terms resulting primarily from the electrostriction and polarization of defects by the EER modulating electric field, and extends the applicability of the attractively simple EER technique to the stu...

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We have constructed a completely quantum-mechanical theoretical treatment of the modification of the local dielectric function by intense electric fields.It includes the numerical calculation of depletion-region bound-state energies and wavefunctions as well as band wavefunctions. We use this treatment to construct electroreflectance (ER) lineshapes.Our numerical results differ significantly from those of previously proposed ER lineshapes for GaAs with Nd >> 101.They yield excellent fits to ER data and allow the accurate determination of doping levels and band bendings from ER data.

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