Temperature-dependent Al/GaAs(110) interface formation and adatom energy references

Synchrotron-radiation photoemission studies of the formation of Al/GaAs(110) interfaces have been performed as a function of substrate temperature for 60T300 K for n- and p-type doped samples. The results show temperature-dependent changes in surface Fermi-level position, surface morphology, and the distribution of released substrate atoms in the overlayer. Detailed examination shows a separation in energy of 1.0 eV for the Al 2p binding energy for n- and p-type GaAs at low coverage. This equals the difference in band bending for the two substrates and demonstrates that the adatom energy reference is an intrinsic level of the semiconductor, not the Fermi level. Substrate band bending approaches its final value when EF becomes the energy reference for the overlayer, and this occurs at the onset of metallic overlayer behavior. Temperature-dependent band bending observed below 1 monolayer can be understood in terms of the coupling of an adsorbate energy level to the semiconductor via steady-state tunneling and thermionic emission. The high-coverage results at all temperatures are consistent with metallicity.