Thickness Dependence in Phase Formation and Properties of TaSe₂ Layers Grown on GaP(111)

The effect of growth temperature and subsequent annealing on the epitaxy of both single- and few-layer TaSe₂ on Se-terminated GaP(111) substrates is investigated. The selective growth of the 1T and 1H phases is shown up to 1 ML according to X-ray and ultraviolet photoelectron spectroscopies. The 1H monolayer, favored at low temperatures, exhibits a very homogeneous coverage after annealing, while the 1T ML, grown at high temperatures, is characterized by a better in-plane orientation. Moreover, X-ray photoelectron diffraction spectroscopy performed on 1T submonolayers shows a negligible amount of mirror twins. By contrast, in multilayers, scanning transmission electron microscopy always reveals a mixture of 2H and 3R polytypes with very few 1T. In addition, the multilayers become Se-deficient above 500 °C, and a new interfacial phase identified as Ta₁₊Se₂ or TaP appears. Finally, the optimized multilayers grown between 250 and 500 °C exhibit a similar metallic behavior with a resistivity comparable to the bulk one with valuable outcomes in the formation of electrical contacts for two-dimensional (2D) material-based devices.