Determination of carrier concentration in n-ZnSe by reflectance difference spectroscopy: Experimental results and model calculation

We have performed in situ and ex situ measurements of reflectance difference (RD) spectra for Cl-doped n-type ZnSe grown by molecular beam epitaxy. The linear electro-optic (LEO) effect (or Pockels effect) in the depletion layer induces characteristic RD features near the E ₁ and E ₁+Δ ₁ transition energy. The intensity of these features is correlated with the carrier concentration determined from capacitance-voltage measurements. A quantitative model is presented to explain the observed dependence of the LEO signal on the carrier concentration. This model quantitatively considers the effect of the finite surface state density. A good fit with the experimental results was obtained by assuming the surface state densities of 3.8×10 ¹³ and 2.6×10 ¹³ cm ^-2eV ^-1, respectively, for in situ measurement of a Se-terminated surface at 300°C and for ex situ measurement of an oxide-covered surface at room temperature.