Effects of glancing-angle ion bombardment on GaAs(001)

The effect of glancing-angle argon ion energy E (0.5–3.0 keV), dose D (0.3–10×1016 ions cm−2), flux J (0.6–5.9×1013 ions cm−2 s−1), impingement angle φ (6°–30°), and substrate temperature Ts (440–650 °C) on the surface morphology and crystallinity of clean and air-exposed GaAs(001) surfaces was studied. For air-exposed GaAs, the lowest roughness measured by atomic force microscopy was 0.3 nm at D=2.3×1016 ions/cm2, E=1 keV, and φ=15° for Ts=570 °C and an ≊1.5×10−5 Torr As4 overpressure. These conditions provided sufficient sputtering to remove surface contamination, as indicated by streaky, 2×4 reconstructed reflection high-energy electron diffraction patterns and C- and O-free low-energy ion scattering spectra, while avoiding ion damage as judged by cross-sectional transmission electron microscopy. Defect-free epitaxial GaAs layers were grown on the sputter-cleaned substrates. Ion bombardment of clean surfaces showed roughening at larger φ values, but smooth surfaces were maintained for φ=6°. Cross-sectional transmission electron microscopy studies of clean bombarded surfaces showed that ion damage decreased with decreasing D, E, and φ, and no damage was observed over a range of conditions. Sputter yields as a function of energy and φ are reported.