X-RAY-INDUCED LOW-TEMPERATURE OXIDATION - N2O/GAAS(110)

We have studied the interaction of N2O with GaAs(110) at 25 K as a function of photon beam exposure, using photoemission to detect and characterize reactions. The results show that x rays (h=1486 and 1253 eV, photon flux 6.8×109 and 2.3×109 photons cm-2 sec-1) induce N2O dissociation and surface oxidation while ultraviolet photons do not within our detectability limit (h=21.2 and 40.8 eV). The primary dissociation process for physisorbed N2O involves the attachment of low-energy secondary electrons created by photoillumination. Following electron capture, N2O dissociation produces O- ions that react with GaAs to yield surface Ga and As oxides. Dissociation also produces N2 molecules that desorb without reacting but can be kinetically trapped at low temperature. The As oxides exhibit As2O5-like, As2O3-like, and intermediate AsOx-like bonding configurations in relative amounts determined by kinetic constraints and oxygen availability. The photon-enhanced formation of a thick oxide at low temperature is limited by diffusion through the oxide layer, and the formation of O2 molecules is observed. Warming to 300 K enhances Ga2O3 growth at the expense of As-O configurations. © 1990 The American Physical Society.