Evolution of empty-state bands for Bi/GaAs(110): From Bi zigzag chains to ordered overlayers

We report studies of Bi-overlayer evolution on cleaved GaAs(110) using energy-dependent, momentum-resolved inverse photoemission (KRIPES) and low-energy electron diffraction (LEED). KRIPES results show a Bi-derived surface resonance at $E_F$+1.25 eV on n-type GaAs(110) for 1–2 monolayer (ML) coverages of Bi. The same feature appears at $E_F$+1.45 eV for p-type GaAs, and the 0.2-eV offset reflects the different Fermi-level pinning for n- and p-type GaAs(110). This Bi-induced feature exhibits no dispersion along Γ¯ X¯’[001] but there is 0.2 eV upward dispersion along [11¯0], consistent with Bi zigzag chain formation, bridging of Ga-As surface atoms along [11¯0], and quasi-one-dimensional character with weak interaction between nearest-neighbor Bi chains. The surface is semiconducting for GaAs(110)-p(1×1) Bi (1 ML) with a gap of ∼0.7 eV, and results for n- and p-type GaAs demonstrate independent development of band offset and barrier height. For Bi layers greater than 1 ML, a new LEED pattern, distorted along [11¯1] or [1¯11], appears and persists to high coverage. For 2 ML, the surface is semimetallic, as reflected by a second Bi-derived empty state at $E_F$+0.35 eV for n-type and $E_F$+0.55 eV for p-type GaAs(110).