###### Abstract  
Cd\({}_{1-x}\)Be\({}_{x}\)Te, a new material with potential for X-ray and \(\gamma\)-ray detectors, was analyzed by photothermal piezoelectric spectroscopy. The samples were tested depending on beryllium content and surface preparation. The main aim of the measurements was to extract the energy gap values, which were found for x = 0.01, 0.03, 0.05, and 0.1. It was shown that mechanical (polishing) and chemical (etching) treatment strongly influenced the amplitude and phase spectra of CdBeTe crystals. Piezoelectric spectroscopy allowed for comparing the quality of preparation of both surfaces for a single sample. The sub-surface damaged layer that was created as a result of surface processing had different thermal parameters than the bulk part of the sample. It was responsible for the additional peaks in the amplitude spectrum and changes in the phase spectrum of the photothermal signal. Two different methods of sample etching were analyzed. One completely quenched the signal, and the other did not eliminate the defects present on the surface after the cutting process. The article presents the preliminary interpretation of experimental data using the modified Blonskij model. photothermal spectroscopy; surface defects; semiconductors +
Footnote †: journal: Physics Letters B  
role, which in high-purity semiconductor devices could become significant due to miniaturization. The effects of the inductively coupled Ar plasma etching on the performance of (111) face CdZnTe detector were investigated by [PERSON] [15], who proposed and analyzed the influence of different solutions for etching. The proposed method could remove the damaged layer caused by mechanical polishing. Still, it also led to the surface composition deviating from the stoichiometric ratio and forming a Te-rich surface. They noticed that the Te-rich layer is a highly conductive region, which results in a large surface leakage current and affects the detection performance. [PERSON] et al. [16] proposed a new chemical mechanical polishing method (silica, hydrogen peroxide, and citric acid), effectively reducing surface roughness. [PERSON] et al. [17] analyzed the effect of hydrogen plasma on CdZnTe and showed that hydrogen plasma could fill the Cd vacancy defect on the surface and reduce the leakage current. Photothermal spectroscopy was also used to investigate the surface treatment procedures and their influence on the surface quality. [PERSON] et al. [18] applied piezoelectric phase spectra to determine both the energy gaps (E\({}_{\text{g}}\)) and the thermal diffusivities of Cd\({}_{\text{x}}\)Zn\({}_{1-\text{x}}\)Se mixed crystals. The authors showed and interpreted the different amplitude and phase spectra characters depending on the surface preparation procedure for Cd\({}_{0.3}\)Zn\({}_{0.7}\)Se and Cd\({}_{0.5}\)Zn\({}_{0.5}\)Se samples. The mechanical (grounding, polishing) and chemical (etching) procedures of surface preparation and their impact on both the amplitude and phase of photothermal spectra were observed for Zn\({}_{1-\text{x}-\text{y}}\)Be\({}_{\text{x}}\)Mn\({}_{\text{y}}\)Se compounds [19]. The surface defects in the samples' sub-surface damaged layer were also reported for ZnSe binary crystal [20]. There are many methods of surface quality testing, e.g., different imaging methods. Piezoelectric photothermal spectroscopy is a cheap and fast method. Other photothermal methods that use microphones or pyroelectrics as detectors are not sensitive (do not show) to effects related to surface states. This is an advantage and a disadvantage; in the case of thermal diffusivity studies in the frequency domain, there is no signal coming from the sub-surface layer, and it is easier to interpret the obtained results (there are well-known models). Still, more investigations and literature data on Cd\({}_{1-\text{x}}\)Be\({}_{\text{x}}\)Te mixed crystals are needed. One article has been published so far [21], which determines thermal properties using the pyroelectric method in the frequency domain.