Electron-Impact Total Ionization Cross Sections of Silicon and Germanium Hydrides

Electron-impact total ionization cross sections of some silicon and germanium compounds have been calculated by applying a new theoretical model that has been found to be reliable for a wide range of molecules. The new theory, the binary-encounter-Bethe (BEB) model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical molecular orbital data—binding energies, average kinetic energies, and occupation numbers—which are readily available from molecular structure codes. Total ionization cross sections of SiH, SiH2, SiH3, SiH4, Si2H6, Si(CH3)4, GeH, GeH2, GeH3, GeH4, and Ge2H6 are presented for incident electron energies T from threshold to 1 keV, and compared to available experimental data. Theory and experiment agree well for SiHx, x=1–4, from thresholds to T<80 eV, while theoretical peaks occur at lower T than experimental peaks for SiHx, x=1–3. No experimental data are available for germanium hydrides for comparison. The theoretical cross sections are given by a compact analytic form suitable for applications in plasma processing. ©1997 American Institute of Physics. History: Received 27 January 1997; accepted 4 March 1997 Permalink: http://link.aip.org/link/?JCPSA6/106/9602/1 Electron-impact total ionization cross sections of silicon and germanium hydrides M. A. Ali Department of Chemistry, Howard University, Washington, DC 20059 Y.-K. Kim, W. Hwang, and N. M. Weinberger National Institute of Standards and Technology, Gaithersburg, Maryland 20899 M. E. Rudd Department of Physics and Astronomy, University of Nebraska–Lincoln, Lincoln, Nebraska 68588-0111 ~Received 27 January 1997; accepted 4 March 1997! Electron-impact total ionization cross sections of some silicon and germanium compounds have been calculated by applying a new theoretical model that has been found to be reliable for a wide range of molecules. The new theory, the binary-encounter-Bethe ~BEB! model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical molecular orbital data—binding energies, average kinetic energies, and occupation numbers—which are readily available from molecular structure codes. Total ionization cross sections of SiH, SiH2, SiH3, SiH4, Si2H6, Si~CH3!4, GeH, GeH2, GeH3, GeH4, and Ge2H6 are presented for incident electron energies T from threshold to 1 keV, and compared to available experimental data. Theory and experiment agree well for SiHx , x51–4, from thresholds to T ,80 eV, while theoretical peaks occur at lower T than experimental peaks for SiHx , x51–3. No experimental data are available for germanium hydrides for comparison. The theoretical cross sections are given by a compact analytic form suitable for applications in plasma processing. © 1997 American Institute of Physics. @S0021-9606~97!00922-7#