Arrays of parallel pores with a diameter of around 60 nm have been introduced by anodic etching in ZnSe single crystals with a free electron concentration of 4 × 1017 cm−3. Porosity-induced Fröhlich vibrational modes were studied by Raman scattering and Fourier transform infrared spectroscopy. The experimental data are compared with the results of theoretical simulation based on the effective medium theory. Traces of Se phase were evidenced at the surface of the porous matrix after anodization, the Raman active modes of this phase being incident in the region of the occurrence of Fröhlich vibrational modes inherent to porous ZnSe. To identify reliably the Fröhlich modes, Raman spectra of porous ZnSe layers were explored under different resonance conditions with several excitation wavelengths and various excitation power densities.
The Hall coefficient, electrical conductivity and electron mobility are investigated in Ag-doped n-ZnSe single crystals at temperatures between 8 and 500 K immediately after doping the samples and after storing them for 5 years under normal room conditions in darkness. The formation of donor-type Ag i interstitial defects stimulated by time is found for the first time. After 5 years storage, the samples show a dramatic increase in the electrical conductivity, free electron concentration and concentration of shallow donors. A model that explains these changes by the displacement of Ag ions into interstitial sites due to lattice deformation forces is proposed. The formation of an Ag-donor impurity band in n-ZnSe:Zn:Ag crystals stored at room temperature is also studied.
The Hall effect, conductivity, mobility, and magnetoresistance of low-resistivity n-ZnSe crystals in the temperature range from 4.2 to 300 K are investigated. At room temperature, the electron concentration of the samples investigated is 2 x 1018 to 5 x 10'' cm+. The maximum electron mobility observed at 60 K is equal to U = 2200 cm*/Vs. Following experimental results are obtained: a maximum on the temperature dependence of Hall cofficient, the negative magnetoresistance in the helium temperatures range described by Toyozawa's theory and discussed assuming the existence of an impurity band in the samples investigated. A model of the impurity band formation in n-ZnSe is proposed and its basic parameters are determined.
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