SCHOTTKY-BARRIER AND INTERFACE FORMATION OF CS GASB(110) AND RB/GASB(110) AT ROOM-TEMPERATURE/

The Schottky-barrier and interface formation of Cs/GaSb(110) and Rb/Ga Sb(110) at room temperature are investigated by soft-x-ray core level photoemission spectroscopy using synchrotron radiation. A large splitt ing (0.9 eV) is found at the Cs 4d core level and indicates two differ ent adsorption sites (having a large difference in ionicity) for the a lkali-metal atoms on the GaSb(110) surface with bonding to both cation and anion. The large Fermi-level overshootings observed at very low a lkali-metal coverages [0.03 monolayer (ML) Cs or Rb] for the p-type Ga Sb(110) samples are directly related to the specific donor character o f alkali-metal atoms with charge transfer into the empty Ga dangling b ond. The unique room-temperature growth properties of alkali metals ar e also likely to be of relevance. Further Cs or Rb deposition is found to be highly disruptive with large reactive components at Sb 4d but a lso Ga 3d core levels and a higher reactivity for the smaller alkali m etal (Rb). Interestingly, this interface reactivity, which results fro m surface defects, is also significantly higher for p-type than for n- type samples, suggesting that the nature of the doping might play some role in the interface chemistry. The final Fermi-level pinning positi on for both p- and n-type GaSb(110) is already achieved at an alkali-m etal coverage of about 0.3 ML, corresponding to significant changes in the mode of growth and to the threshold of surface disruption. This p inning position is located at about 0.1 eV above the valence-band maxi mum, in agreement with a defect acceptor state model.