TEMPERATURE DEPENDENCE OF PbSe-AgSbSe2 SINGLE CRYSTALS’ ELECTRICAL CONDUCTIVITY

Bridgman’s horizontal method was used for growing of single crystals. Detailed synthesis samples, methods of crystal growth and phase equilibrium diagram of the PbSe-AgSbSe₂ system are presented in [1, 2]. Single crystals of PbSe-AgSbSe₂ solid solution complied with blend composition of 0, 5 and 8 mol% AgSbSe₂. The research of temperature dependence of PbSe-AgSbSe₂ single crystals’ electrical conductivity was carried out in the temperature range of 77-300 K. The samples with an average size of 6×2×1 mm³ were used for this research.
 

The research results of the temperature dependence of the electrical conductivity of single crystals PbSe-AgSbSe₂ are presented in Fig.1. At low temperatures (~77-180 K), electrical conductivity (σ) of single crystals PbSe (0 mol.% AgSbSe2) remained almost unchanged on temperature shift, what accords with work data [1], according to which the state of PbSe single crystals is close to degenerated one, because concentration holes in PbSe at room temperature p≈6 10¹⁸ cm^-3. At the temperature range of 180-300 K ~ σ decreases with increasing temperature, which may indicate the onset of metallic conductivity.

The samples of 5 mоl. % AgSbSе₂ have showed the properties similar to those ones of the degenerated semiconductor at the temperature range of 77-230 K_. At T = 230 K there is a sharp change in electrical properties (Fig. 1.2) of single crystals of this volume components, which may be due to a change in the mechanism of metallic conductivity into semiconductor one (Mott transition).

Temperature dependence of the electrical conductivity of single crystals of 92 % PbSe–8% AgSbSe₂ at temperatures 180-300 K ~ can be described by the dependency:
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which is set in accordance to the slope σ(T) in the Arrhenius coordinates (Fig. 1.3) thermal activation energy (Е_А) was Е_А1≈0,2 еV; prior multiplier was σ_А≈10⁵ Om ∙ cm^-1. It is known that the value σ_A is inherent for transitions of carriers from defect centers in the bandgap, which are close to the Fermi level (Е_f), to the delocalized states of permitted band [5], in our case, to the flow below of the valence band. Obviously, the conductivity in the temperature range of 180-300 K is a particular conductivity. In such case the provisions Е_f is close to the middle of the semiconductor bandgap (Е_f=Еg/2). Respective, the thermal bright of the bandgap is Е_g=2 Е_А≈0,4 eV.

At the temperature range of 120-180 K the dependence σ(T) is exponential (Fig.1). In accordance with the slope σ(T) the determined activation energy values were Е_А2≈0,02 eV. Considering that the studied crystals appeared to be compounds of p-type conductivity, the temperature activation energy Е_А≈0,02 eV in the temperature range 120-180 K can be interpreted by thermal excitation holes of shallow acceptor centers in the valence band.

References:

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