Growth of germanium monosulfide (GeS) single crystal by vapor transport from molten GeS source using a two-zone horizontal furnace

Abstract To drive the research and development of two-dimensional (2-D) germanium monosulfide (GeS) applications, a more facile method for obtaining (GeS) single crystals is required. To that end, we first improved the method for synthesizing polycrystalline GeS to reduce the reaction time and prevent the explosion of the quartz ampoule, and this step was carried out inside a horizontal furnace. We also successfully grew a GeS single crystal without a seed crystal by melting this polycrystalline GeS inside a closed, evacuated quartz ampoule using a two-zone horizontal furnace and then employing a vapor transport method. The growth ampoule was specifically designed to prevent the molten GeS from flowing from the evaporation side to the growth side, where the crystal grew through an evaporation–recondensation transition in the temperature range of 654 to 660 ℃. Single-crystal X-ray diffraction patterns were recorded to precisely determine the crystal structure, which revealed that the grown crystal was a GeS single crystal with an orthorhombic structure of the GeS-type (space group Pnma) and lattice parameters of a = 10.5284 (10), b = 3.6584 (3), and c = 4.3166 (4) A. A differential thermal analysis confirmed that the melting point of the grown GeS crystal was 664 ℃.