Growth and thermal stability studies of layered GaTe single crystals in inert atmospheres

Highlights: • GaTe single crystals have successfully been grown by a temperature gradient technique. • GaTe is thermally stable up to 700K in an Ar atmosphere and up to 935K in a N₂ atmosphere. • Thermal annealing under N2 gas at temperatures below 673 K increases the PL intensity through the crystallinity enhancement. In this study, we investigated the thermal stability properties in inert atmospheres of GaTe single crystals fabricated by a temperature gradient technique. The obtained crystals possess a monoclinic layered structure with high crystalline quality. To explore the thermal stability of GaTe, the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed up to 1173K in N₂ and Ar atmospheres. GaTe crystals are thermally stable up to 700K in Ar and stable up to 935K in N₂ due to the protective role of the physically adsorbed N₂ molecules on GaTe surface. Annealing effect on the structural and optical properties of GaTe were examined after thermal treatment in N₂ atmosphere at different temperatures; 573, 673, 773, and 873K. Three prominent Raman modes at 97cm⁻¹ (A_g), 145cm⁻¹ (A_g), and 158cm⁻¹ (B_g) corresponding to the monoclinic GaTe phase almost remained, suggesting no structural damage at elevated temperatures. Especially, the photoluminescence (PL) intensity is improved as the annealing temperature increases and reaches a maximum at 673K owing to the enhancement in the GaTe crystallinity. Above 873K, we observed a significant reduction in the PL intensity, which is attributed to the vacancies induced by tellurium evaporation.