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The energy gap of the modification of silver selenide stable below 133°C has been investigated. Studies of the optical-absorption spectrum at 80 °K and at 5°K and of the temperature variation of the Hall coefficient and electrical conductivity have been made on polycrystalline samples. Analysis of the data on the electrical properties in the intrinsic region suggests the existence of two phases, not distinguishable by x-ray diffraction, with energy gaps E 0 at 0°K of 0.07±0.01 eV and 0.18±0.01 eV, respectively. The latter value agrees with that proposed for the /3 2 phase of j3-Ag 2 Se reported by Baer. The optical-absorption spectra suggest that the band-to-band transitions observed are direct. The extrapolated threshold of absorption is at 0.13 eV at 5°K and correlates best, because of the probable Burstein shift of the absorption edge, with the proposed value of £0=0.07 eV. It is also concluded that the energy gap increases as the temperature decreases.

The study of electrical properties of β-Ag2Te and β-Ag2Se has been extended to 4.2°K. The former compound was zone refined without decomposition. Both n- and p-type samples of β-Ag2Te were studied; all samples of β-Ag2Se prepared were n type to 4.2°K. Neither semiconductor showed any indication of extrinsic carrier freeze-out or of impurity banding. Study of oxygen as a possible acceptor in β-Ag2Te showed no significant effect; a selenium-doped sample of β-Ag2Se was n-type to 4.2°K.

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