Structural and electronic properties of Pb1-xCdxTe and Pb1-xMnxTe ternary alloys

A systematic theoretical study of two PbTe-based ternary alloys, Pb1-xCdxTe and Pb1-xMnxTe, is reported. First, using ab initio methods we study the stability of the crystal structure of CdTe - PbTe solid solutions, to predict the composition for which rock-salt structure of PbTe changes into zinc-blende structure of CdTe. The dependence of the lattice parameter on Cd (Mn) content x in the mixed crystals is studied by the same methods. The obtained decrease of the lattice constant with x agrees with what is observed in both alloys. The band structures of PbTe-based ternary compounds are calculated within a tight-binding approach. To describe correctly the constituent materials new tight-binding parameterizations for PbTe and MnTe bulk crystals as well as a tight-binding description of rock-salt CdTe are proposed. For both studied ternary alloys, the calculated band gap in the L point increases with x, in qualitative agreement with photoluminescence measurements in the infrared. The results show also that in p-type Pb1-xCdxTe and Pb1-xMnxTe mixed crystals an enhancement of thermoelectrical power can be expected.Comment: 10 pages, 13 figures, submitted to Physical Review

Thermoelectric studies of electronic properties of ferromagnetic GaMnAs layers

Thermoelectric power, electrical conductivity, and high field Hall effect were studied over a broad temperature range in ferromagnetic Ga₁₋xMnxAs epitaxial layers (0.015 ≤ x ≤ 0.06). Thermoelectric power analysis gives information about carrier transport mechanisms in layers with both metallic and non-metallic types of conductivity and allows determination of the Fermi energy and carrier concentration. At high temperatures (T > 70 K), the thermoelectric power in GaMnAs linearly increases with increasing temperature. That indicates the presence of a degenerate hole gas with the Fermi energy EF = 220 ± 25 meV, nearly independent of Mn content (for 0.02 ≤ x ≤ 0.05). At lower temperatures, GaMnAs layers with metallic-type conductivity show an additional contribution to the thermoelectric power with the maximum close to the Curie temperature

Fermi Level Position in GaMnAs - a Thermoelectric Study

Thermoelectric power was studied in the temperature range 100≤ T≤300 K in 0.3-1μm thick ferromagnetic Ga$\text{}_{1-x}$Mn$\text{}_{x}$As epitaxial layers (0.015≤ x≤0.06) in order to determine Fermi energy E$\text{}_{F}$ and carrier concentration p. For 0.015≤ x≤0.05, at T=273 K we find E$\text{}_{F}$=275±50 meV and p=(2.5± 0.5)×10$\text{}^{20}$ cm$\text{}^{-3}$ (approximately Mn content independent). For x= 0.06, the Fermi energy decreases by about 100 meV with the corresponding reduction of hole concentration to p=1.2×10$\text{}^{20}$ cm$\text{}^{-3}$. At T=120 K, these parameters vary between E$\text{}_{F}$=380 meV and p=3.5×10$\text{}^{20}$ cm$\text{}^{-3}$ for x=0.015 to E$\text{}_{F}$=110 meV and p=5×10$\text{}^{19}$ cm$\text{}^{-3}$ for x=0.06

Pb1−x\text{}_{1-x}Mnx\text{}_{x}Te Crystals as a New Thermoelectric Material

We studied experimentally thermoelectric properties of p-type bulk crystals of Pb$\text{}_{1-x}$Mn$\text{}_{x}$Te and Pb$\text{}_{1-x-y}$Ag$\text{}_{y}$Mn$\text{}_{x}$Te (0≤ x≤ 0.083 and y≤0.017) at room and liquid nitrogen temperatures. Model calculations of the thermoelectric figure of merit parameter (Z) involved the analysis of carrier concentration, carrier mobility, density of states as well as electronic and lattice contributions to the thermal conductivity of PbMnTe. In the analysis we took into account the main effect of Mn concentration on the band structure parameters of PbMnTe, i.e. the increase of the energy gap. The analysis of electrical, thermoelectric, and thermal properties of Pb$\text{}_{1-x}$Mn$\text{}_{x}$Te crystals showed that, at room temperature, the maximum values of the parameter Z occur in crystals with Mn content 0.05≤ x≤0.07 and are comparable with a maximal value of Z observed in PbTe. At T=400 K the increase in the parameter Z by 10% is expected in Pb$\text{}_{1-x}$Mn$\text{}_{x}$Te crystal (as compared to PbTe) for a very high concentration of holes of about p=5×10$\text{}^{19}$ cm$\text{}^{-3}$. The experimental data correctly reproduce the theoretical Z(p) dependence