Comparison of the results of optical and electrophysical measurements of the concentration of conduction electrons in $n$-InSb samples

The infrared reflection spectra of $n$-InSb single-crystal samples doped with tellurium were studied at room temperature. Using dispersion analysis, the spectral dependences of the real and imaginary parts of the permittivity were obtained and the loss function was constructed. The values of the characteristic wave number corresponding to the high-frequency plasmon-phonon mode were determined and the values of the optical electron concentration, $N_{\mathrm{opt}}$, were calculated. Electrophysical measurements were performed on the same samples using the van der Pauw method at room temperature and the values of the Hall concentration, $N_{\mathrm{Hall}}$, were determined. It was shown that for all the studied samples, the optical concentration exceeds the Hall concentration. It was suggested that the surface layers of the samples are enriched with free electrons. The thickness of the surface layer of the sample, in which the reflected light signal is formed, was estimated and shown to be no more than 1 $\mu$m.