UPS and LEED studies of GaAs (110) and (111) As surfaces

Abstract

By comparison of LEED intensity–voltage data on GaAs (110) surfaces prepared by cleaving and by chemical etch followed by sputter annealing, we find the surfaces to be essentially the same in atomic geometry within the limits of experimental error. However, we find that important distinctions can be made between (110) surfaces prepared by these two methods when Fermi-energy pinning and UPS data are considered. In this regard, we show that Fermi-energy pinning is a particularly sensitive indicator of the degree of surface perfection and that the UPS data gives valuable information about the degree of perfection achieved by the different surface preparation techniques used. As an example of this, we show differences in the spatial distribution of damage on sputter-annealed and heat-cleaned surfaces which are seen by UPS. The sputtered surface is extremely imperfect prior to annealing. Finally, we find no evidence for intrinsic filled surface states in the band gap on the (111) As surface when prepared by heat cleaning or sputter annealing.

Charge Redistribution at GaAs/P3HT Heterointerfaces with Different Surface Polarity

“…For calculations of bulk GaAs, the integration over the Brillouin zone was performed using a k-points grid of 8 × 8 × 8 during the cell optimization and electronic properties calculations. We have obtained a lattice constant of a = 5.543 Å, which is close to the experimental value of a = 5.653 Å. GaAs( 110) and (111)B surface orientations were selected to study the effects of surface polarity; they are stable surfaces observed in the experiments, 46,47 110) and (111)B surfaces and GaAs/P3HT interfaces. All surface and interface geometries were optimized with the method of Broyden−Fletcher−Goldfarb−Shanno (BFGS) until all of the forces on all atoms became lower than 0.02 eV/Å and total energy difference between two optimization steps of the minimization procedures was <10 −4 eV.…”

“…For calculations of bulk GaAs, the integration over the Brillouin zone was performed using a k -points grid of 8 × 8 × 8 during the cell optimization and electronic properties calculations. We have obtained a lattice constant of a = 5.543 Å, which is close to the experimental value of a = 5.653 Å. GaAs(110) and (111)B surface orientations were selected to study the effects of surface polarity; they are stable surfaces observed in the experiments, , and both top layers terminate with As atoms. For the calculations of the GaAs slabs, in-plane lattice parameters of GaAs(110) and GaAs(111)B surfaces were obtained from optimization of the corresponding bulk GaAs.…”

Paramagnetic Mn impurities on Ge and GaAs surfaces

“…The clean Ge͑100͒ and Ge͑111͒ surfaces showed the characteristic low energy electron diffraction ͑LEED͒ patterns of the ͑2 ϫ 1͒ and c͑2 ϫ 8͒ reconstructions, respectively, in agreement with literature data. 22,23 GaAs͑110͒ also showed the expected ͑110͒ LEED pattern, 24 but the precise stoichiometry of the surface remained undetermined, as preferential sputtering of As is likely to lead to Ga-rich surface layers. After cleaning, no surface oxidation was detected by x-ray absorption spectra ͑XAS͒ at the oxygen K edge.…”

Surface characterization

“…Surface photovoltage spectroscopy was used to demonstrate photo-induced transitions between surface state levels and the subsequent ejection of electrons into the conduction band (295). The degree of surface perfection of GaAs(llO) surfaces prepared by cleaving and by chemical etching followed by sputter annealing was measured using LEED and UPS (370). The electronic and geometrical structure of the cleaved GaAs(llO) surface was measured using UPS (321); models of the surface Ga and As atom motion are proposed.…”