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.

Electrical Properties of β‐Ag2Te and β‐Ag2Se from 4.2° to 300°K

Narrow Gap Semiconductors

In this paper, we report a solution-phase synthesis of silver telluride and bismuth telluride nanowire heterostructure using tellurium (Te) nanowire as sacrificial template and site-selective conversion strategy. High-resolution transmission electron microscope studies confirm sharp interface with possible epitaxial growth between silver telluride and bismuth telluride regions. Through tuning the precursor amount (bismuth and silver precursors) during the reaction, the composition between silver telluride and bismuth telluride can be adjusted. Moreover, the mass produced powder of nanowire heterostructure is consolidated into nanocomposite pellets, and thermoelectric properties of the nanocomposite pellets are investigated between 300 and 400 K. Results show that our materials are p-type with reduced lattice thermal conductivity and a ZT of ∼0.41 at 400 K, which is the best reported value for p-type silver telluride.

Thermoelectric Properties of Silver Telluride–Bismuth Telluride Nanowire Heterostructure Synthesized by Site-Selective Conversion

The Hall coefficient, resistivity, and Seebeck coefficient of $n$- and $p$-type specimens of ${\mathrm{Ag}}_{2}$Te have been measured over the temperature range from 55 to 300\ifmmode^\circ\else\textdegree\fi{}K. These results indicate that the compound is highly degenerate over the whole temperature range studied. Calculations were made of the effective masses, mobility ratios, and energy gap and gave order of magnitude values.

Degeneracy in Ag 2 Te

The energy gap of the modification of silver selenide stable below 133\ifmmode^\circ\else\textdegree\fi{}C has been investigated. Studies of the optical-absorption spectrum at 80\ifmmode^\circ\else\textdegree\fi{}K and at 5\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}K of 0.07\ifmmode\pm\else\textpm\fi{}0.01 eV and 0.18\ifmmode\pm\else\textpm\fi{}0.01 eV, respectively. The latter value agrees with that proposed for the ${\ensuremath{\beta}}_{2}$ phase of $\ensuremath{\beta}\ensuremath{-}{\mathrm{Ag}}_{2}\mathrm{Se}$ 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\ifmmode^\circ\else\textdegree\fi{}K and correlates best, because of the probable Burstein shift of the absorption edge, with the proposed value of ${E}_{0}=0.07$ eV. It is also concluded that the energy gap increases as the temperature decreases.

J.F. Walsh

Papers

Electrical properties of Ag2Te