Effect of a phase transition on the electron energy spectrum in Ag 2 S
- PDF / 169,096 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 98 Downloads / 174 Views
TRONIC AND OPTICAL PROPERTIES OF SEMICONDUCTORS
Effect of a Phase Transition on the Electron Energy Spectrum in Ag2S F. F. Aliev^, M. B. Jafarov, B. A. Tairov, G. P. Pashaev, A. A. Saddinova, and A. A. Kuliev Institute of Physics, Azerbaijan National Academy of Sciences, pr. G. Dzhavida 33, Baku, 370143 Azerbaijan ^e-mail: [email protected] Submitted April 26, 2007; accepted for publication December 20, 2007
Abstract—Temperature dependences of electrical conductivity σ, Hall coefficient R, and thermopower α0 in Ag2S are reported. It is established that at T ≈ 435 ± 5 K, all kinetic parameters vary drastically, which is associated with a change in parameters of the conduction band. It is shown that the dispersion law of electron energy in β-Ag2S corresponds to the Kane model. PACS numbers: 71.20.Nr, 72.20.Fr, 73.50.Lw DOI: 10.1134/S1063782608100023
starting from the concentration n ≈ 2.1 × 1019 cm–3, indicates that conductivity is carried out by a single carrier type. The constancy of α0(T) in β-Ag2S disagree with the data on σ(T) and R(T). Based on the data on α∞ and R∞ (α∞ and R∞ are the thermopower and Hall coefficient in a high magnetic field), it is known that if only a single carrier type contributes to conductivity, we can determine the effective mass of charge carriers at the conduction band bottom and at the Fermi level. By the value of α∞, we determined the value of the reduced chemical potential η*, and then, by the data on the Hall coefficient, calculated the effective mass at the conduction band bottom m *0 and the value of m* at the Fermi level. Our calculated
1146
σ, Ω–1 cm–1 1 104 2 3 4 5 2 10
100
10–2
~ ~
It is known that Ag2S at T ≈ 435 ± 5 K transforms from the low-temperature monoclinic α phase into the high-temperature body-centered cubic (bcc) phase [1]. During the phase transition, parameters of the band structure substantially vary, which leads to radical variations in electrical and thermoelectrical properties. In contrast to other silver chalcogenides (Ag2Se and Ag2Te [2–4]), Ag2S possesses a wider band gap and low charge-carrier mobility in the α phase [1]. Temperature dependences of band parameters of the β phase are studied poorly, which makes attractive the study of the behavior of kinetic coefficients in β-Ag2S. In this study, in order to obtain data on band parameters and the dispersion law of the energy of charge carriers, electrical and thermoelectric properties of β-Ag2S are examined in wide concentration and temperature ranges. The samples are obtained by the standard technology [5]. Studies show that, during the phase transition, conductivity σ increases by several orders of magnitude, while the Hall coefficient R and thermopower α0 decrease by a factor of ~3–4 (Figs. 1–3). After the phase transition, σ and R, excluding R for the samples with the concentration n ≈ 6.25 × 1018 cm–3, decrease as the temperature increases, while α0 is independent of temperature. From the dependence R(T) for the samples with the concentration n < 6.25 × 1018 cm–3 (Fig. 2), it is evident th
Data Loading...
