The high-quality SnSe 2 single crystal was successfully synthesized using the temperature gradient method. N-type characteristic and strong anisotropic transport properties of SnSe 2 single crystal were exhibited between ab-plane and c-axis. At 673 K, the power factor (PF) value along ab-plane is 3.43 -1 while it along c-axis is . The ratio between thermal conductivities along ab-plane(κ ab ) and along c-axis (κ c ) is 7.6 order at 300 K, while as at 673 K, this value about 5.6. The thermoelectric figure of merit ZT along c-axis (0.15) is higher than that (0.1) along the ab-plane, according to the ultralower out-of-plane thermal conductivity. The electronic band structure results, which were examined by angle-resolved photoemission spectroscopy (ARPES) predicted the potential of improving thermoelectric performance of SnSe 2 single crystal by electron doping.

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In this work, pure, large Br-doped SnSe2 single crystals were successfully synthesized using the temperature gradient technique. Br acts as a donor, resulting in electron concentrations up to ∼6.83 × 1019 cm–3 at room temperature. All samples exhibited metal-like electrical resistivities and Seebeck coefficient behaviors over a temperature range of 300–673 K. Br doping greatly improved the power factor, especially along the in-plane direction. We observed anisotropy in the electrical conductivity, Seebeck coefficient, and, most notably, thermal conductivity. An ultralow thermal conductivity was achieved along the out-of-plane direction, leading to a maximum ZTc of 0.54 at 673 K in the Br-doped sample, which is twice as large as that of the in-plane direction, ZTa = 0.25.

Gallium Telluride (GaTe), a layered material with monoclinic crystal structure, has recently attracted a lot of attention due to its unique physical properties and potential applications for angle-resolved photonics and electronics, where optical anisotropies are important. Despite a few reports on the in-plane anisotropies of GaTe, a comprehensive understanding of them remained unsatisfactory to date. In this work, we investigated thickness-dependent in-plane anisotropies of the 13 Raman-active modes and one Raman-inactive mode of GaTe by using angle-resolved polarized Raman spectroscopy, under both parallel and perpendicular polarization configurations in the spectral range from 20 to 300 cm−1. Raman modes of GaTe revealed distinctly different thickness-dependent anisotropies in parallel polarization configuration while nearly unchanged for the perpendicular configuration. Especially, three Ag modes at 40.2 ($${\text{A}}_{\text{g}}^{1}$$ A g 1 ), 152.5 ($${\text{A}}_{\text{g}}^{7}$$ A g 7 ), and 283.8 ($${\text{A}}_{\text{g}}^{12}$$ A g 12 ) cm−1 exhibited an evident variation in anisotropic behavior as decreasing thickness down to 9 nm. The observed anisotropies were thoroughly explained by adopting the calculated interference effect and the semiclassical complex Raman tensor analysis.

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