Fig. 1: In situ control of MoTe₂ polymorphs during wafer-scale synthesis.

a Schematic of the Te-gas confined reactor consisting of Ni_xTe_y on top of a Mo precursor film within the furnace. b, c Optical microscopy (OM) images of MoTe₂ at the growth temperatures of (b) T = 500 °C for the growth time, t = 20 min and (c) T = 700 °C. Rounded shapes in (c) indicate the 2H-phase MoTe₂. d Polymorphic phase diagram of MoTe₂ as a function of T and t, determined by the difference of optical contrast in the OM images (Supplementary Fig. 2). Linear interpolation was performed for the contour plot using data points (bullets). e Optical image of the synthesized 1T’- and 2H-phase MoTe₂ on a 4-inch wafer, with atomic force microscopy (AFM) images showing their thickness (H) (scale bar: 2 μm). f Raman spectra of the resultant 2H- (blue) and 1T’-MoTe₂ (orange). g X-ray photoelectron spectroscopy (XPS) spectra of the Te 3d level for 2H- (blue) and 1T’-MoTe₂ (orange) grown at T = 700 °C for t = 30 min and T = 500 °C for t = 10 min, respectively. Dashed lines indicate Te-Mo binding energies (E_b) of MoTe₂. h Summary of the H and surface roughness (R_a) of MoTe₂, depending on the H of the pre-deposited Mo precursor (H of pre. Mo). The average and standard deviation of five areas (~10 \(\times\) 10 μm²) are represented as data points ± error bars. i Refractive index (n; lighter color) and extinction coefficient (k; darker color) values of 1T’- (red) and 2H-phase MoTe₂ (blue) obtained via ellipsometer measurements. j Absorption coefficient (α) of our MoTe₂ film in the broad wavelength range (~300–1300 nm) compared with bulk semiconductors (e.g., Si⁷⁶ and Ge⁷⁷) and 2D transition-metal dichalcogenides (e.g., MoS₂, MoSe₂, and MoTe₂ flakes)⁵⁰, demonstrating its higher absorption efficiency.