## 3 Results  
### Cut and Grounded Samples  
First, cut and grounded samples were examined. Figure 2 presents the experimental amplitude (blue) and phase (green) spectra of Cd\({}_{0.97}\)Be\({}_{0.03}\)Te in the rear configuration at the frequency modulation of 126 Hz. In both spectra, the theoretical simulations for the ideal sample are presented (in black). The different characters of both experimental and simulated spectra are visible. There are two additional maxima in the sub-bang gap region for the amplitude and the significant change (at the energy of E = 1.46 eV) of the phase in the same area. The amplitude signal in the above bandgap area is increasing in comparing stable values in simulated amplitude spectra. Similar behavior was previously observed for Zn\({}_{1-x-y}\)Be\({}_{x}\)Mn\({}_{y}\)Se compounds [19]. It was associated and interpreted as coming from the defects located on the surface of the sample and strictly connected with the method of surface preparation. Figure 3 presents amplitude (a, b) and phase (c, d) spectra for Cd\({}_{0.99}\)Be\({}_{0.01}\)Te grounded mixed crystals for different frequencies of modulation frequency and the rear (a, c) and front (b, d) configurations. In this case, the character of amplitude and spectra deviates from the theoretical predictions. For the lowest frequency (12 Hz), the additional maximum visible for higher frequencies is not visible. The higher the frequency, the higher the intensity of the maximum below the energy gap will be compared to the area above the energy gap: as the modulation frequency increases, the thermal diffusion length decreases, and the signal is generated from a smaller thickness. For low frequencies, the signal comes from a large sample thickness, and the signal from the surface is not dominant. It is worth noting that  
Figure 2: (**a**) Experimental amplitude (blue) and (**b**) phase (green) spectra of Cd\({}_{0.95}\)Be\({}_{0.05}\)Te in the rear configuration at the frequency modulation of 126 Hz. The solid black lines simulate the ideal crystal’s theoretical amplitude and phase spectra. regardless of the frequency, the points of inflection of the curves are observed in the phase spectra for the same energies. The different amplitude and phase spectra characters were observed for the Cd\({}_{0.9}\)Be\({}_{0.1}\)Te mixed crystal. Figure 4 presents amplitude (a) and phase (b) spectra for this sample. Figure 4: Amplitude (**a**) and phase (**b**) spectra for Cd\({}_{0.9}\)Be\({}_{0.1}\)Te grounded mixed crystal for different frequencies of modulation frequency for the front configuration at 12 Hz (blue lines), 36 Hz (cyan line), 76 Hz (green lines), and 126 Hz (red lines). Figure 3: Amplitude (**a**,**b**) and phase (**c**,**d**) spectra for Cd\({}_{0.99}\)Be\({}_{0.01}\)Te grounded mixed crystal for different frequencies of modulation frequency for the rear (**a**,**c**) and front (**b**,**d**) configurations at 12 Hz (blue lines), 76 Hz (green lines), and 126 Hz (red lines). Two maxima are observed for this sample in the amplitude spectra of E\({}_{1}\) = 1.51 eV and E\({}_{2}\) = 1.59 eV. The first one is present for all the frequencies, and its intensity is not changed compared to the intensity of the signal in the region above the energy gap. The behavior of the second maximum is similar to the one observed in the previous sample. A probable cause is that the thickness of the damaged layers on both surfaces is different. In the phase spectra, one must analyze the maxima and bending points to identify the localization of defects and their energetic positions. Beryllium and defects related to its presence in the subsurface layer are undoubtedly responsible for changes in spectra and the formation of additional peaks. A strong correlation between surface preparation for Zn\({}_{1-\mathrm{x-y}}\)Be\({}_{\mathrm{x}}\)Mg\({}_{\mathrm{y}}\)Se [26] was previously observed, but no explanation has yet been found for the mechanisms of the formation of defects on the surface; research is ongoing to clarify their nature.