Single-photon ionization and detection of Ga, In, and Asn species in GaAs growth

In this paper, single photon ionization time-of-flight mass spectroscopy (SPI-TOFMS) is used to monitor chemical fluxes of In, Ga, and Asn, relevant in molecular beam epitaxy of GaAs. With single photon ionization at 118 nm (10.5 eV), the photon energy is large enough to ionize the species, but not sufficient to ionize and fragment. The lack of molecular dissociation of species such as As2 and As4 greatly simplifies the interpretation of mass spectra. SPI-TOFMS provides the ability to measure densities, and hence fluxes, of multiple chemical species above a substrate noninvasively and in real time during conventional molecular beam epitaxy. The relative ionization efficiencies of Ga and the Asn species at 118 nm are determined. Additionally, this laser probing technique is used to study the isothermal and temperature programmed desorption of arsenic from Si(100). The catalytic cracking of As4 on Si is also examined and discussed. This technique promises to be a valuable in-situ optical diagnostic for III-V and II-VI molecular beam epitaxy.