J. R. Power

Evidence of electron confinement in the single-domain (4×1)-In superstructure on vicinal Si(111)

Reflectance anisotropy spectroscopy is applied to submonolayer growth of In on the vicinal silicon (111) surface. Deposition in the region of 1 monolayer onto a clean stepped Si(111) surface at elevated temperature produces a single-domain In-induced (4×1) superstructure consisting of quasi-one-dimensional chains aligned parallel to the vicinal surface step edges. A significant optical anisotropy (1.65%), uncharacteristic of semiconductor systems, develops in the region of 1.9 eV which saturates upon completion of the (4×1) superstructure. We relate this feature to an optical transition involving a flat, highly populated filled surface state observed previously. We argue that the intensity and direction of this peak are indicative of electronic confinement within this system perpendicular to the In-induced chain length.

The influence of monolayer coverages of Sb on the optical anisotropy of vicinal Si(001)

Abstract The influence of monolayer coverages of antimony (Sb) on vicinal silicon (001) is studied by reflectance anisotropy spectroscopy (RAS). Adsorption of Sb at room temperature, which is known to break the Si dimer bond and to cause step reconstruction, changes the shape of the RAS spectrum completely, even before annealing. An interesting feature appears in the region of 3.7 eV, which sharpens when the system is annealed to 300°C to form the Si(001)-(1 × 1)-Sb structure. Our results support the view that Si(001)-(1 × 1)-Sb is a distinct phase and we associate the 3.7 eV peak with optical transitions involving SiSb backbonds. Further annealing to 550°C forms Si(001)-(2 × 1)-Sb, where the Sb atoms are now dimerised. This heat treatment decreases the vicinal surface domain imbalance by splitting up the double-height steps, and the RAS signal is reduced in size. Annealing to 750°C causes Sb desorption and the formation of the 0.25 ML Si(001)-c(4 × 4)-Sb structure, with an increase in optical anisotropy, which we attribute to double-height steps reforming as the Sb dimer-induced strain in the system is alleviated. Complete desorption of Sb restores the Si(001)-(1 × 2) structure, and the original RAS signal.

Effect of adlayer dimer orientation on the optical anisotropy of single domain Si(001)

The effect of adlayer dimer formation on the optical anisotropy of single domain Si(001) is reported. Reflection anisotropy spectroscopy (RAS) from Ga and Sb adsorbed on the Si(001) surface reveals complex behavior which depends strongly on the atomic species and the RAS signal cannot be simply related to dimer orientation. Dimer formation in the same direction on the surface by Si and Ga is shown to produce RAS signals, below the direct optical gap of Si, of the opposite sign. This contrasts with the simpler behavior observed for Ga and As adsorption on GaAs(001) surfaces.

REFLECTANCE ANISOTROPY SPECTROSCOPY STUDY OF THE SURFACE RECONSTRUCTIONS OF DECAPPED INP(001)

A reflectance anisotropy spectroscopy (RAS) and low-energy electron diffraction study of the InP(001) surface is presented. The surface was prepared by thermal desorption of an As-P capped epilayer grown by molecular beam epitaxy. RA spectra have been monitored over a spectral range of 1.5–5.5 eV at regular intervals during thermal decapping and annealing up to the point of decomposition (553–973 K). Each of the RA spectra of the surface reconstructions comprise positive (at 2.9 eV) and negative (at 1.8 eV) anisotropies which have been previously associated with P- and In-related bonding, respectively. Unlike other III-V (001) semiconductor surfaces, the evolution of different reconstructions cannot be explained in terms of a change in surface stoichiometry which involves loss of the anion species. In the case of InP(001) the P species contributes to the clean surface reconstruction from the early stages of decapping to the point of decomposition.

The effect of submonolayer coverages of Ga on the optical anisotropy of vicinal Si(001)

Abstract The effect of submonolayer (ML) coverages of gallium on vicinal Si(001) has been investigated using reflectance anisotropy spectroscopy (RAS). A feature at 1.8 eV is sensitive to different annealing conditions and has been associated with optical transitions of the Si(001) (2 × 2)-Ga structure involving Ga dimers. The Si(001) (2 × 2)-Ga structure is stable to annealing to 600°C. The 1.8 eV feature is still evident after deposition of 1.5 ML Ga at room temperature, indicating that some Ga dimers from the (2 × 2)-Ga structure are still present at these coverages.

Complementary vibrational and reflectance anisotropy spectroscopic determination of molecular azimuthal orientation

Abstract Azimuthal orientations of 9-anthracene carboxylate (9-AC) on clean and p(2×1)O/Cu(110) surfaces were determined from a reflectance anisotropy spectroscopy (RAS) signal derived from an intramolecular electronic transition. The magnitude of the molecular signal on the p(2×1)O/Cu(110) surface is 4–5 times larger than on the clean surface. We present a complete vibrational assignment of adsorbed 9-AC based on Fourier transform infrared and on- and off-specular high resolution electron energy loss spectroscopy (HREELS) and ab initio calculations. Correlation of the off-specular HREELS on p(2×1)O/Cu(110) with the RAS results demonstrates that the magnitude of the RAS signal depends on the degree of azimuthal orientation.

Adsorbate-induced reconstruction on Si(001) probed by resonant optical second harmonic generation

Abstract The recent development of easily tuneable pulsed lasers has made spectroscopic optical second harmonic generation (SHG) studies routinely possible, although little work has been published. Spectroscopic SHG from Si(001) surfaces in the region of 3.3 eV is reported here. Adsorption of Sb on a clean Si(001)-1 × 2 surface, followed by annealing, produces Si(001)-1 × 1-Sb and then Si(001)-2 × 1-Sb. The results obtained are consistent with an unusual model of the Si(001) 1-Sb surface structure, which comprises isolated Sb atoms bonded to two bulk-like Si atoms. The Sb atoms only form dimers on further annealing to produce the Si(001)-2 × 1-Sb structure.