R. Cimino

Schottky barrier heights and interface chemistry in Ag, In, and Al overlayers on GaP(110)

We have carried out a study of the chemical reaction of silver, indium, and aluminium layers with cleaved GaP(110) surfaces using photoemission with synchrotron radiation. Core level photoelectron spectra show that silver and indium overlayers do not cause an interface reaction with GaP(110). The deposition of Al, on the other hand, leads to an extensive exchange reaction which also proceeds at low temperature, although influenced by changes in overlayer growth morphology. Surface band bending induced by the metallic overlayers was investigated as a function of deposition for n‐ and p‐type material. In contrast to earlier findings, almost identical Schottky barrier heights for In and Ag deposition are obtained, despite the large difference in work function between these two metals. Results for Al also suggest that a small range of pinning positions is responsible for the Schottky barrier heights for junctions of these metals with GaP(110). We find that large peak shifts due to a surface photovoltage induc...

Non-equilibrium effects in photoemission from metal-semiconductor interfaces

Abstract It has recently been shown that the determination of surface band bending in clean and adsorbate-covered semiconductor surfaces may be seriously affected by non-equilibrium processes induced by the photoemission soft X-ray light source. These effects are often large enough to completely mask the actual equilibrium band bending. We present a compilation of experimental data and model calculations which clearly establish the wide-ranging nature of such effects, and their influence on previous studies of metal overlayers on the (110) surfaces of III–V semiconductors, which have been used as model systems in the past. It is demonstrated that metallization of the overlayer does not seem to play a role in establishing the Schottky barrier, as was previously believed. More recent applications of surface photovoltage, for example in the study of laterally resolved recombination centers at surfaces, are also discussed.

A photoemission study of H2O adsorption on a vicinal Si(100) surface

Abstract A high-resolution core and valence band photoemission study of the clean and H 2 O-covered vicinal one-domain Si(100) surface is presented. The Si 2p core level analysis of the clean reconstructed surface shows two surface core level shifts at −0.52 and 0.39 eV binding energy with respect to the bulk peak. After dosing to saturation coverage of H 2 O, two main chemically shifted components are found at 0.31 and 1.00 eV binding energy. These are assigned to Si surface atoms bonded to H and OH respectively. The valence band photoemission spectra are also interpreted in terms of dissociative adsorption, and a limited application of angle-resolved photoemission selection rules allows the probing of the adsorption geometry.

The growth of bismuth and antimony overlayers on InP(110)

The adsorption of Bi and Sb on clean cleaved InP(110) surfaces has been studied with soft x‐ray photoemission spectroscopy at the BESSY synchrotron radiation source in Berlin. Bi and Sb were deposited onto ultrahigh vacuum cleaved InP(110) surfaces at substrate temperatures of 300 K [room temperature (RT)] and 120 K [low temperature (LT)]. In this paper we focus on the evolution of the overlayer emission intensities as a function of coverage. Spectra of the Bi 5d and Sb 4d core level emission lines were taken from the submonolayer regime up to coverages of approximately 60 and 20 monolayers (ML) of Bi and Sb, respectively. The spectra were then deconvoluted using a core level fitting routine. In all cases, good agreement between the experimental and fitted curves was achieved by introducing two chemically shifted components of the Bi 5d and Sb 4d core level emission which are interpreted in terms of Bi(Sb)–substrate and Bi(Sb)–Bi(Sb) bonds. However, for RT deposition, the evolution of the Bi 5d and Sb 4d ...

Surface photovoltage effects in photoemission from metal/GaP(110) interfaces: Temperature‐dependent Fermi level movement

In recent experiments of metal deposition onto cleaved GaP(110) surfaces we have shown that light sources used in photoelectron spectroscopy may induce a surface photovoltage (SPV), which causes a substantial deviation from the ground state potential distribution, and may induce errors in the determination of band bending by photoemission. Here we analyze the temperature‐dependent movement of the surface Fermi level in n‐ and p‐type GaP(110) surfaces as a function of indium and silver deposition, taking into account the presence of the SPV. It is found that changes in the substrate temperature not only modify the adlayer morphology and metallicity, but also the surface electron‐hole recombination rate. We observe that the temperature‐dependent shift of the semiconductor core levels is always accompanied by a similar shift of the metal core level and Fermi edge, suggesting that the reversible temperature‐dependent band bending recently reported for metal/III–V semiconductor interfaces is related to the SPV...

Temperature effects on the formation of the Sb/InP(110) interface

Abstract The adsorption of Sb on UHV cleaved InP(110) surfaces was studied for substrate temperatures of 300 K (RT) and 100 K (LT) using high resolution soft X-ray photoemission spectroscopy. The In 4d, Sb4d core levels, and the valence band emission were monitored from submonolayer coverages of Sb up to around 20 monolayers. At LT Sb is found to form a homogeneous amorphous film rather than islands on an ordered first monolayer as observed at RT. Furthermore, Fermi level shifts were derived from energy shifts in the In 4d emission lines. Complementing the different overlayer growth modes the Fermi level shift gradually increases with Sb coverage at LT, whereas at RT a Sb coverage of 0.5 ML leads to a maximum shift which is diminished with the completion of the first ordered monolayer.

Line broadening in semiconductor core level photoemission induced by barrier height inhomogeneity

High resolution core level photoemission spectra from clean GaAs(110) semiconductor surfaces are analyzed considering the possibility of local barrier height variations at the surface. A simple model calculation is presented and is used to predict the effects of such local variations on the line shape of Ga 3d and As 3d core level emission. We clearly show that the presence of differently pinned zones on the surface leads to an extra broadening which may mask some of the important information usually extracted by conventional core level fitting analysis. By discussing the Ga 3d and As 3d line shape changes, which occur as a function of temperature, we give experimental evidence that barrier height fluctuations can indeed be present and can strongly affect core level photoemission spectra.

Photoemission study on non-equilibrium effects in metals on GaAs(110)

Abstract We have carried out photoemission studies of the band bending at interfaces between In and low and highly doped GaAs(110) surfaces. Here we show that non-equilibrium phenomena are present at these interfaces. Surface photovoltage dominates at low substrate temperatures and low doping levels. To correctly take into account the experimental results obtained on junctions formed between In and highly p-doped semiconductor surfaces we consider the possibility that the photoemission process itself can induce non-equilibrium process, driving the metal/p-semiconductor diode into reverse bias. We have also investigated the temperature dependence of such phenomena. An analysis of the relative intensities and energies of the Ga 3d and In 4d core levels enables us to separate shifts induced in the surface Fermi level by the change in overlayer morphology from those shifts brought about by a variation in magnitude of non-equilibrium effects. This analysis confirms that, together with surface photovoltage, a different non-equilibrium process has to be considered.

Temperature-dependent interface formation study of aluminium on GaP(110)

Abstract The interaction of aluminium with cleaved GaP(100) surfaces is important in the investigation of Schottky barrier formation since ideal Schottky behaviour has been reported for a number of metals on GaP(110). AlGaP(110) provides an interesting example of a reactive interface, with limited AlGa exchange reaction occurring at room temperature (RT). Metal reactivity has been invoked as a possible cause of the deviation from the classical Schottky model reported for this interface at RT. We present high resolution core level photoemission data recorded with synchrotron radiation for the interfaces formed at room and low temperature (LT). The study of interface evolution is based on intensity and line shape analysis of the Ga(3d) and Al(2p) core level photoemission features. We investigate the reactions produced at the interface, model the evolving interfacial morphology and assess possible changes of reactivity. Our results show that the cation exchange reaction is not strongly reduced at LT whereas the growth mode of the aluminium layer and the formation of gallium interface species are significantly affected by the substrate temperature. Results are discussed in comparison with the widely studied AlGaAs(110) and AlInP(110) systems.

Growth mode and temperature-dependent morphology of indium on GaP(110)

Abstract The growth of indium layers on cleaved GaP(110) surfaces has been studied by core- and valence-level photoelectron spectroscopy, in order to elucidate the growth mode and morphology of such layers. In order to provide a basis for the analysis of the metal-covered surface, the surface core-level shifts of the clean GaP(110) surface have been characterized in detail. We find a three-dimensional growth mode (indium clusters) at room temperature, whereas low-temperature deposition leads to a kinetically limited (Poisson-type) quasi-laminar growth. Metallic In clusters and a Fermi edge were identified at coverages as low as 0.5 monolayers. Line-shape analysis of the In4d and Ga3d levels shows that the interface exhibits weak reactivity, both at room and low temperature. Annealing of indium layers deposited at low temperatures, however, leads to the appearance of a reacted indium component. These data are discussed in comparison with the behaviour of other metal overlayers on compound semiconductor surfaces.