Gas Phase Reactions Determined by In Situ Mass Spectrometric Investigation for GeSn Chemical Vapor Deposition Processes

GeSn alloy has gained significant attention for its compatibility with Si photonics platforms and its engineerable bandgap covering mid-infrared (MIR) wavelengths. Chemical vapor deposition (CVD) is widely used to synthesize GeSn materials. However, a fundamental understanding of the growth mechanism must still be developed. This research used mass spectrometry to investigate CVD gas phase reactions at various temperatures of 25 °C, 100 °C, 150 °C, and 200 °C for a gas mixture of GeH 4 and SnCl 4 with various gas partial pressure ratios ( p SnCl 4 /p GeH 4 ) of 0.002, 0.005, 0.01 and 0.042. The analysis of the experimental results indicates two types of gas phase reactions occurred in all scenarios examined. The reactions involve direct interactions between SnCl 4 and GeH 4 , as well as the decomposition of GeH 4 . The hybrid radicals of Sn, H 3 SnCl/SnCl , the Germanium hybrid fragments of H 3 GeCl/GeCl , H 2 GeCl 2 /GeCl 2, and GeH x and hydrogens ( H , H 2 , and H 3 + ) are the primary products of the first and second types of reactions, respectively. These reactions exhibit increased reactivity at higher temperatures, and the resulting intermediates are essential for the GeSn CVD process. Density functional theory-based thermochemical calculations agree with the experimental results and indicate that the proposed chemical reactions are either exothermic or minimally endothermic.