Gas-phase ion chemistry in GeH 4/C 2H 4/XH 3 (X = P, N) systems

Abstract

The C 2H 4/PH 3, C 2H 4/NH 3, GeH 4/C 2H 4/PH 3 and GeH 4/C 2H 4/NH 3 gaseous mixtures were studied by ion trap mass spectrometry, with the aim of finding the best experimental conditions leading to the formation of Ge/C/P (or N) ion clusters. In fact, these species are possible precursors of semiconductor materials based on germanium carbides, doped with P and N, and prepared by chemical vapour deposition methods from suitable gaseous systems. For the binary mixtures the rate constants of the main processes were determined and compared with collisional rate constants in order to calculate reaction efficiencies. For the ternary mixtures the mechanisms of ion/molecule reactions yielding Ge, C and P (or N) ion clusters were studied. In the GeH 4/C 2H 4/PH 3 system, formation of Ge m C n P p H s + ions was observed only from C/P ions reacting with germane, the C/P ions being formed with good yields through ion/molecule reactions in the ethene/phosphine system. In the ammonia-containing mixtures, the yield of C/N ions is quite poor because most of the reactions observed lead to ammonium ion formation, which is unreactive under the experimental conditions used. Furthermore, the amounts of Ge m C n H s + and Ge m N n H s + ion products were found to be small and weakly reactive and no processes leading to Ge/C/N ions were detected in the GeH 4/C 2H 4/NH 3 mixture.