Long-range ordering of Sb multilayers on GaAs(110): Evolution of resonant inverse photoemission.

Abstract

Temperature- and coverage-dependent ordering of Sb multilayers on GaAs(110) has been investigated with use of inverse-photoemission spectroscopy (IPES) and low-energy electron diffraction. IPES studies show that an empty state at ${\mathit{E}}_{\mathit{F}}$+0.3 eV resonates for incident electron energies of ${\mathit{E}}_{\mathit{i}}$=16.2 eV because the radiative decay of a plasmon within the Sb film (\ensuremath{\Elzxh}${\mathrm{\ensuremath{\omega}}}_{\mathit{p}}$=15.9 eV) competes with conventional inverse photoemission. The resonance is first observed at \ensuremath{\sim}3.5 monolayers (ML) as the empty-state feature shifts from \ensuremath{\sim}0.4 eV at 3 ML to \ensuremath{\sim}0.3 eV at 3.5 ML for Sb overlayers grown on GaAs(110) at 300 K and annealed to 475 K. The empty structure is associated with long-range ordering of the Sb multilayers rather than Sb-As antibonding states at the interface. The thin film structure and the thickness of the film play critical roles in determining the empty-state resonance. Structural studies for 20-\AA{} Sb films show ringlike diffraction patterns with the coexistence of (1\ifmmode\times\else\texttimes\fi{}1) structures and fractional-order spots adjacent to integer-order spots along [11] or [11\ifmmode\bar\else\textasciimacron\fi{}]. The ringlike structures are attributed to hexagonal basal planes of individual Sb crystallites that are randomly rotated and oriented parallel to the (110) surface. Two equivalent quasihexagonal domains are observed during the initial growth stages. These results suggest a correlation between the resonance and growth phases consisting of long-range-ordered (110) domains with Sb crystallites in between.