Monitoring and enhancing molecular beam epitaxy using glancing angle low energy ions

The effects of glancing-angle argon ion energy E, dose D, flux J, impingement angle {dollar}phi{dollar}, and substrate temperature {dollar}Tsb{lcub}rm s{rcub}{dollar} on the surface morphology and crystallinity of clean and air-exposed GaAs(001) surfaces was studied. Ion bombardment conditions were determined that provided sufficient sputtering to remove surface contamination, as indicated by reflection high energy electron diffraction (RHEED) and ion scattering spectroscopy (ISS), while avoiding ion damage as judged by cross-sectional transmission electron microscopy (XTEM). Defect-free epitaxial GaAs layers were grown on the sputter-cleaned substrates. XTEM studies of clean bombarded surfaces showed that no damage was observed over a range of conditions.; The effects of glancing-angle argon ion on the surface morphology and crystallinity of air-contaminated Si(001) surfaces were also studied using bombardment angles {dollar}phi = 3spcirc{dollar} and 15{dollar}spcirc{dollar} from the surface at different values of the substrate temperature {dollar}Tsb{lcub}rm s{rcub}{dollar}, energy E, and dose D. Room temperature bombardment yielded smooth clean surfaces with barely resolvable pits after defect-etching.; With the above information on ion bombardment effects, an ISS geometry is described that minimizes sputtering and ion damage. The key feature is the use of a glancing-incidence-angle Ar ion beam: Ar ions provide better mass resolution than He while the glancing angle minimizes sputtering. ISS measurements of 1-ML-thick InAs films on GaAs(001) were made using 1.1 keV Ar ions at {dollar}phi = 3spcirc{dollar} and a 56{dollar}spcirc{dollar} scattering angle. No change in the In peak was observed after 25 minutes of continuous ISS scans corresponding to a dose of {dollar}{lcub}sim{rcub}1.6times10sp{lcub}16{rcub}{dollar} ions-cm{dollar}sp{lcub}-2{rcub}{dollar}.; A new ion beam monitoring technique was also developed that utilizes the advantages of glancing-angle ions. Specular scattering of 3 keV He ions was observed for incidence angles of 2-6{dollar}spcirc{dollar} from GaAs(001). During molecular beam epitaxy, the scattered ion current dropped rapidly upon opening the Ga shutter, showed damped oscillations, and then increased gradually upon closing the shutter. The oscillation periods corresponded to monolayer growth times. Oscillation amplitudes decreased with increasing substrate temperature indicating a transition to step-flow growth. The oscillations were not a diffraction effect, allowing a quantitative interpretation based on scattering by adatoms and step edges.