Stuart J. Hoekje

Bio: Stuart J. Hoekje is an academic researcher from University of Florida. The author has contributed to research in topics: Auger electron spectroscopy & Spectroscopy. The author has an hindex of 3, co-authored 3 publications receiving 33 citations.

XPS study of chemically etched GaAs and InP

Abstract: The surface composition of p‐type GaAs etched in HCl or Br2 in methanol, and n‐type InP etched in HCl, H2SO4, HNO3, or Br2 in methanol has been studied by means of x‐ray photoelectron spectroscopy (XPS). The surface compositions of GaAs and the binding energy of the surface As atoms vary with the etching solution and with the extent of oxidation of the surface. The full width at half‐maximum of the Ga(3p) photoelectron peak increases upon exposure of etched GaAs to air. The XPS results are compared with Schottky barrier heights previously measured for similarly prepared surfaces with Pb contacts. The amount of oxidized P on InP surfaces is higher after an HNO3 etch than after HCl, H2SO4, or Br2/methanol treatments. An HCl etch leaves an unoxidized slightly In‐rich surface.

Structure-sensitive oxidation of the indium phosphide (001) surface

Abstract: The oxidation of anion- and cation-rich indium phosphide (001) has been investigated by exposure to unexcited molecular oxygen. Indium phosphide oxidation is an activated process and strongly structure sensitive. The In-rich δ(2×4) surface reacts with oxygen at 300 K and above. Core level x-ray photoemission spectra have revealed that the O2 dissociatively chemisorbs onto the δ(2×4), inserting into the In–In dimer and In–P back bonds. By contrast, the P-rich (2×1) reconstruction does not absorb oxygen up to 5×105 Langmuir at 300 K, as judged by the unperturbed reflectance difference spectrum and low energy electron diffraction pattern. Above 455 K, oxygen reacts with the (2×1) inserting preferentially into the In–P back bonds and to a lesser extent into the phosphorus dimer bonds.

Ultraviolet-Ozone Cleaning of Semiconductor Surfaces

Abstract: : The ultraviolet (UV)/ozone surface-cleaning method, which is reviewed in this report, is an effective method of removing a variety of contaminants from silicon (as well as many other) surfaces. It is a simple-to-use dry process which is inexpensive to set up and operate. It can rapidly produce clean surfaces, in air or in a vacuum system, at ambient temperatures. In combination with a dry method for removing inorganic contamination, the method may meet the requirements for the all-dry cleaning methods that will be necessary for future generations of semiconductor devices. Placing properly precleaned surfaces within a few millimeters of an ozone-producing UV source can produce clean surfaces in less than one minute. The technique can produce near-atomically clean surfaces, as evidenced by Auger electron spectroscopy, ESCA, and ISS/SIMS studies. Topics discussed include the variables of the process, the types of surfaces which have been cleaned successfully, the contaminants that can be removed, the construction of an UV/ozone cleaning facility, the mechanism of the process, UV/ozone cleaning in vacuum systems, rate-enhancement techniques, safety considerations, effects of UV/ozone other than cleaning, and applications.

Chemical and Thermal Stability of Alkanethiol and Sulfur Passivated InP(100)

Abstract: InP(100) surfaces treated with Na2S·9H2O and CnH2n+1SH are examined by contact angle measurement, X-ray photoelectron spectroscopy, and atomic force microscopy to determine the chemical and thermal behavior of these passivated surfaces. The surfaces coated by octadecanethiol (n = 18) self-assembled monolayers (SAMs) are found to be more stable toward oxidation than the S-passivated surface. The chemical stability of octadecanethiol SAMs in various environments is examined. The thiol monolayer is found to be stable in 0.1 M HCl but degrades in 0.1 M NaOH, boiling chloroform, and water. The behavior of these surfaces at elevated temperatures under a vacuum is also investigated. The octadecanethiol-coated InP(100) is stable up to 473 K, above which the films begin to degrade. Unlike other substrates on which the entire molecule including the sulfur headgroup desorbs together, on InP, the sulfur headgroup remains on the surface even after annealing to 673 K. These observations suggest that the desorption occu...

Application of low energy ion scattering to oxidic surfaces

Abstract: Low-energy (0.1-10 keV) ion scattering (LEIS) is used for the determination of the atomic composition and structure of oxide surfaces. Its extreme surface sensitivity enables the selective analysis of the outermost atomic layer. It is precisely this layer that is largely responsible for many chemical and physical properties of oxides. Lowering of the surface energy provides a strong driving force for segregation to the surface. Surface segregation is very important at temperatures that are high enough to enable diffusion. Since the surface enrichment is often restricted to the outermost atomic layer, the unique capability of LEIS to analyze this layer selectively, is one of the main applications of the technique. Other applications pertain to studies of the mechanism of oxidation of metals, semiconductors and to that of the growth of oxides on itself and on other materials. For equilibrated surfaces of spinels (powders or sintered) both LEIS and chemical methods show that, while cations in octahedral sites are accessible, cations in tetrahedral sites are not. This suggests that the equilibrium surfaces of these oxides are dominated by only one or two crystallographic planes. For single crystals, blocking, shadowing and focussing effects of the incident ions or scattered ions have been used to determine the location of surfce atoms as well as the presence and annealing characteristics of surface defects. Although the number of such studies are very limited, the results show great promise for the understanding of oxide surfaces.