Single-photon laser ionization time-of-flight mass spectroscopy (TOF-MS) is used to monitor fluxes of As4, As2, and Ga, species that are important in molecular-beam epitaxy of GaAs. With this technique, fluxes of multiple chemical species above a substrate can be measured noninvasively and in real time during conventional molecular-beam epitaxy. Additionally, the geometry of the single-photon ionization TOF-MS permits simultaneous film-growth monitoring by using techniques such as reflection highenergyelectron diffraction (RHEED). Here gas-phase arsenic and gallium beams are ionized by a single 118-nm (10.5-eV) photon and detected with a TOF-MS. The 118-nm photons are produced by frequency tripling 355-nm light from a pulsed Nd:YAG laser in Xe. With single-photon ionization, less than 0.4% ofthe As4+ signal fragments to As2+. Neither As4+ nor As2+ fragments to As+ at 118 nm. The relative ionization probability of As4/As2 at 118 nm is approximately 4:1. This technique promises to be a powerful tool for analyzing most III-V and II-VI molecular-beam epitaxy growth species.
© 1993 Optical Society of America
Paul G. Strupp, April L. Alstrin, Russell V. Smilgys, and Stephen R. Leone, "Single-photon laser ionization time-of-flight mass spectroscopy detection in molecular-beam epitaxy: application to As4, As2, and Ga," Appl. Opt. 32, 842-846 (1993)