In situ mass spectrometric investigation to probe GeSn growth dynamics and mechanisms in the chemical vapor deposition processes

GeSn has attracted increasing attention due to its tunable bandgap from indirect to direct resulting in unique electronic and optoelectronic capabilities. Chemical vapor deposition (CVD) is well acknowledged as an advanced growth method for GeSn, demonstrating its capability with grown materials for infrared lasers and detector development. As an in situ diagnostics of the CVD process, a residual gas analyzer (RGA) could enable the detection of all gaseous species during growth, thus probing the growth dynamics and mechanism. Therefore, it is highly desirable but is lacking in the (Si)GeSn research community. This work utilized an RGA equipped with a specialized differential vacuum pumping system to analyze the mass spectra of the GeSn CVD precursors of SnCl4, GeH4, and their combination. The spectra of SnCl4 collected from gas samples at a standard base pressure of 0.3 Torr display consistent fragments with central mass-to-charge ratios (m/z) of 78, 120, 155, 225, and 260, corresponding to Sn+, SnCl2+, SnCl+, SnCl2+, SnCl3+, and SnCl4+, respectively. These profiles closely resemble those observed in the National Institute of Standards and Technology and Wiley and Matsumoto et al. The simultaneous introduction of SnCl4 and GeH4 at a combined pressure of several tens of Torr yields spectra, indicating a chemical reaction that produces GeCl4 at room temperature in the vacuum chamber and tubing. Utilizing Gaussian16 and ORCA codes, the ab initio and density functional thermochemistry computations were employed to predict potential essential reactions and validate the experimental findings.