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Measurements are made on optical absorption from 350 to 2500 nm at 77 °K of ZnS crystals irradiated by fast neutrons at room temperature and of those fired in a zinc or sulfur vapour at 1100 °C. It has been found that neutron irradiation produces photoinsensitive 2.7 and 1.75 eV bands in addition to the 3.5, 3.2, 2.9, and 2.3 eV bands reported previously, and that the firing in zinc vapour produces new photosensitive 3.2, 2.7, and 1.75 eV bands. All of the six bands produced by neutron irradiation are also produced by the firing in zinc vapour. However these bands can not be produced by the firing in sulfur vapour, which produces four bands different from those induced by the zinc firing. It is proposed that the 3.5, 3.2, 2.7, and 1.75 eV bands are related with sulfur vacancies and that the 2.7 and 1.75 eV bands are due to hole transitions.

In electron-irradiated ZnSe, the ESR signal due to the V-center which is a single hole trapped at a zinc vacancy has been observed by Watkins /l/, and the optical property of the center has been reported /2, 3/. In ZnS, the F+ center which is a single electron trapped at a negative ion vacancy is introduced by high-energy particle irradiation o r heat treatments and produces the 2.3 and 2.9 eV optical absorption bands /4 to 6/, but the F+ center in ZnSe has not yet been reported. On the other hand, the peaks of the emission bands analogous to Cu-B and Cu-G emissions in ZnS shift to lower energies a s the mole fraction x in ZnS1-xSex mixed crystals is increased /7/. Therefore it may be expected that the peak of the F+ center absorption band in ZnSl-,Sex mixed crystals shifts to lower energies with increasing x similarly to the emission peaks. In this note, the absorption spectra in neutron irradiated ZnSo. 5Se0. crystals were measured at 77 K. and ZnSeThe crystals used in this work were ZnSo. 5Se0. mixed crystals grown from the.melt in a high pressure vessel and ZnSe crystals grown by the sublimation method. The specimens were polished mechanically and their typical size was specimens, respectively 1) Koyama, Tottori 680, Japan.

Undoped high‐quality p‐type and Cu‐doped CdTe crystals are characterized by admittance spectroscopy (AS) and photoluminescence (PL) measurements in order to analyze the residual impurities. An improved method is proposed for the analysis of “freezing‐out steps” in AS. The method permits to determine the activation energies, the concentrations, and the compensation ratios of the uncompensated shallowest acceptors. Cross‐check using AS and PL indicates that the residual copper impurity strongly affects the electrical and optical properties of the high‐quality p‐type CdTe crystals.

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