Trace Water Detection in Phosphine By Cavity Ring-down Spectroscopy

ABSTRACTWe are using cavity ring-down spectroscopy (CRDS) to measure concentrations of water in nitrogen and, for the first time to our knowledge, in phosphine. Water vapor concentrations have been measured in purified and unpurified phosphine, indicating a water mole fraction of (22.0 ± 1.0) x 10-6 in unpurified phosphine. After purification with an in-line, chemically-reactive purifier, the mole fraction of water in phosphine was less than 0.1 × 10-6. Mole fractions as high as (730 ± 60) × 10-6 have been measured in unpurified phosphine, suggesting that the H2O vapor concentration increases substantially with time as the gas is stored in a cylinder. The materials properties of AlInP grown by molecular beam epitaxy (MBE) with CRDS-characterized PH3 were found to be relatively insensitive to water contamination at the 22 mol/mol level.