In situ analysis using molecular beam-mass spectrometry-application to crystal growth

A molecular beam sampling technique which consists of a three stage differentially pumped system with expansion through a diverging conical nozzle in the first stage is described. The gasdynamics for the expansion through the conical nozzle sampling orifice was characterized by probing the gas density distribution of the flow field inside the nozzle with a movable conical skimmer orifice. Palladium diffused hydrogen was analyzed and the major impurity species detected were H2O, CO and CH4 in the ppm range. A proposed reaction between quartz and hydrogen at elevated temperature was confirmed by the detection of SiO in the vapor at concentration levels close to levels predicted from existing thermodynamic data. The influence of these impurities on the liquid epitaxial growth of GaAs is discussed.