Surface modification of GaAs(110) by low-energy ion irradiation

The GaAs(110) surface was exposed to normal-incidence Ar+ ion bombardment at energies ranging from 200 eV to 3 keV. The structural, electronic, and compositional modifications induced were monitored by low-energy electron diffraction, electron energy-loss spectroscopy (EELS), and by Auger-electron spectroscopy for different flux densities, accumulated fluences, and specimen temperatures. The fluences necessary for the amorphization of the near-surface region at room temperature amount to some 1x1015 Ar+/cm2 and increase both with decreasing flux density and with decreasing impact energy, the latter effect being very pronounced below 1 keV. The alterations of the electronic states as inferred from EELS exhibit a similar fluence dependence but are less sensitive to the bombardment energy. Prolonged ion irradiation causes an As depletion of the surface which saturates at fluences ≥1x1016 Ar+/cm2, again dependent on the impact energy and flux density. The steady-state Ga/As surface concentration ratio (cGa/cAs)∞ is 1.25 (relative to the bulk composition) at 200 eV and increases to ∼1.45 at 3 keV. These surface composition changes are reduced for ion bombardment at elevated specimen temperatures and almost no variations are observed with the sample held at 730 K