Fig. 5: h-GaTe to m-GaTe phase transformation and phase stability as a function of film thickness.

a Low-temperature Raman spectra of 18 ML h-GaTe transformed into m-GaTe after RTA at 550^∘C for 30 min. The laser excitations are 473 nm and 632.8 nm. b Low-temperature PL spectra from Si substrate (gray), 18 ML GaTe in the as-grown h-GaTe (red) and m-GaTe after RTA (blue). The inset shows the power dependence of the PL peak at 1.635 eV measured with 532 nm laser excitation wavelength at 10 K with superlinear slope (m) of the excitonic recombination and saturation of the defect-related channel at higher power. c, d Raman spectra of h-GaTe as-grown and after RTA, respectively, for 4, 6, 12, 18 layers. The vibrational modes from h-GaTe and m-GaTe are highlighted with circles and stars, respectively. e Low-temperature PL spectra of h-GaTe films after RTA compared with the as-grown (a/g) 18 ML h-GaTe. Both Raman and PL are excited with 473 nm laser. In order to preserve the material integrity and to protect it from oxidation, all the samples have been capped with Si₃N₄ before annealing.