Gamma-irradiation effect on electron–phonon coupling in Ge-doped CdTe crystals: Raman and photoluminescence study

An impact of different doses (10–500 kGy) of γ-irradiation on electron–phonon coupling in Ge-doped CdTe (CdTe:Ge) single crystals was investigated via low-temperature (T=5 K) photoluminescence (LTPL) and resonant Raman scattering (RRS). In the present work electron–phonon coupling concerns longitudinal optical (LO) phonons and was described in terms of Huang–Rhys factor. It was obtained γ-irradiation in such dose range leads to the increases in the value of Huang–Rhys factor. At high doses (equal to 200 kGy) the saturation of the increased at low doses Huang–Rhys factor was observed. Based on the features of radiation-stimulated changes in LTPL, increasing of electron–LO–phonon coupling can be explained by radiation-induced defect compensation process involving, with the great probability, Ge dopant atoms filling of native cadmium vacancies (VCd) and by other related mechanisms such as radiation-induced Ge clusters dissociation. Such compensation is resulted in the proving of the crystalline perfection of irradiated crystals. The latter was confirmed by resonant Raman scattering measurements. Resonant Raman conditions for near E0+Δ0 gap (2,54 eV at 80 K) were obtained by temperature tuning of the band gap keeping the excitation energy fixed for laser excitation energies near E0+Δ0. It was found good agreement in the dose dependencies of the values of Huang–Rhys factors and 2LO/1LO phonon modes ratio obtained from resonant Raman spectra. The increasing in the intensity of Fröhlich-induced 2LO-phonon modes with the increase of the irradiation dose and decreasing in impurity-induced 1LO-phonon intensity indicates about decreasing in the defect concentration in studied crystals. Relatively high saturation dose corresponding to the 2LO/1LO phonon modes ratio indicates high radiation strength of studied material.