N-type Barrier Height Research Articles

MnAs∕GaAs∕MnAs: Morphology and interfacial properties

The properties of epitaxial MnAs/GaAs/MnAs epilayers grown on GaAs(111)B substrates are investigated. The different steps of the growth are detailed from the buffer layer to the top MnAs layer using scanning tunneling microscopy. Despite the high quality of the bottom MnAs surface, uncovered regions of MnAs are observed when the low-temperature-grown GaAs overlayer thickness is 3 nm, while a continuous barrier is formed for an overlayer thickness of 7 nm. The interfacial electronic properties of GaAs/MnAs and MnAs/GaAs are examined with x-ray and ultraviolet photoemission spectroscopy, indicating an absence of detectable reactivity between GaAs and MnAs. Two monolayers of MnAs over GaAs are metallic with a bulk-like valence band. In addition, an n-type barrier height of 0.7 eV is estimated for MnAs/GaAs/MnAs.

Defect-driven inhomogeneities in Ni∕4H–SiC Schottky barriers

Nanoscale depth-resolved cathodoluminescence spectroscopy (DRCLS) of Ni diode arrays on 4H-SiC epitaxial wafers reveals a striking correspondence between deep level defects and electrical transport measurements on a diode-by-diode basis. Current-voltage measurements display both ideal and nonideal diode characteristics due to multiple barriers within individual contacts. Near-interface DRCLS demonstrates the presence of three discrete midgap defect levels with 2.2, 2.45, and 2.65eV emission energies whose concentrations vary on a submicron scale among and within individual diodes, correlating with barrier inhomogeneity. These results also suggest that SiC native defect levels can account for the maximum range of n-type barrier heights.

CoSi2/Si(111) Interface Structure and its Influence on the Schottky Barrier

ABSTRACTThe interface structure and Schottky barrier height Of CoSi2/Si(111) interfaces may be controlled by manipulating the thin film growth conditions. Single crystal CoSi2 films on Si(111) were prepared by ultra-high vacuum processing, analyzed electrically by currentvoltage techniques, and characterized structurally by plan-view and cross-section high resolution transmission electron microscopy (HRTEM) and transm-ission electron diffraction (TED). Interfaces exhibiting n-type barrier heights ranging from 0.27 to 0.69 eV, and p-type barrier heights ranging from 0.43 eV to over 0.71 eV were prepared -by varying the processing conditions. HRTI3M and TED revealed the existence of a √3 × √3 interface reconstruction for the low barrier n-type/high barrier p-type samples. Possible models of the interface reconstruction are discussed.

Photoemission study of the growth, desorption, Schottky-barrier formation, and atomic structure of Pb on Si(111)

We have utilized high-resolution synchrotron-radiation photoemission spectroscopy and high-energy electron diffraction to study the various reconstructed surfaces of Pb-covered Si(111). The Si 2p and Pb 5d core levels and valence bands are analyzed as a function of Pb coverage and annealing temperature. We confirm the room-temperature (RT) Stranski-Krastanov growth mode with the two-dimensional adlayer completed at \ensuremath{\sim}1.3 monolayers. The formation of the Schottky barrier has been studied. We measure n-type barrier heights of 0.89 and 1.09 eV for the RT epitaxial phase and the (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} incommensurate phase, respectively. Possible mechanisms that may be responsible for the disagreement between barrier heights as measured by core-level photoemission and electrical techniques are discussed. We also report on the observation of surface-shifted core levels and surface states in the valence band for the (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} phases obtained by annealing to higher temperatures in the desorption regime. These results are used for an investigation of the structural models for these surface phases.

Electrical properties of copper-silicon Schottky barriers

The electrical properties of Cu-Si(100) Schottky barriers formed by the deposition of Cu on lightly doped (1014-1015 cm-3) n-type and p-type Si(100) have been studied in the temperature range 80-295 K using current-voltage and capacitance-voltage techniques. Deep-level transient spectroscopy was used to determine Cu-related energy levels in Si and X-ray photoemission spectroscopy to monitor the reaction between Cu and Si. In both n-type and p-type Si(100), no Cu-related levels deeper than approximately 0.1 eV below (above) the conduction-band edge (the valence-band edge) and with concentrations above 1011 cm-3 were observed after copper deposition or after silicide formation. Silicide formation was found to have very little or no effect on the barrier height and its temperature dependence. For both the as-deposited Cu and the reacted Cu3Si silicide phase, the temperature coefficient of the n-type barrier height was found to be almost equal to that of the indirect band gap in Si. The p-type barrier height did not exhibit a temperature dependence. These results suggest that the Fermi level at the interface is pinned relative to the valence-band edge. These results deviate significantly from the predictions of models of Schottky-barrier formation based on Fermi-level pinning in the centre of the semiconductor indirect band gap.

Temperature dependence of the Schottky-barrier height of tungsten on n-type and p-type silicon

The Schottky-barrier heights of W and its silicide WSi 2 on both n-type and p-type Si(100) have been measured in the temperature range 77–295 K with the use of current-voltage and capacitance-voltage techniques. Auger-electron and X-ray photoemission spectroscopies were used to characterize the Si(100) surfaces prior to metal deposition, and to monitor the reaction between W and Si. Silicide formation has very little or no effect on both the barrier height and its temperature dependence. The n-type barrier height for both the metal and the reacted silicide phase decreases with increasing temperature with a coefficient almost equal to the temperature coefficient of the indirect band gap in Si. The p-type barrier height does not exhibit a temperature dependence. These results suggest that the Fermi level at the interface is pinned relative to the valence-band edge. These results deviate from the predictions of models of Schottky-barrier formation based on the suggestion of Fermi-level pinning in the center of the semiconductor indirect band gap. Along with results previously reported for metal(silicide)-Si systems with a wide range in metal electronegativity, the present results show that both the silicon barrier height and its temperature dependence are affected by the metal.

The synthesis and properties of low barrier Ag-Ga intermetallic contacts to n-type GaAs

It is demonstrated that uniform silver-gallium alloy films, containing up to 30% gallium, can be controllably and reproducibly fabricated by electron-beam evaporation from a single alloy source. As expected from bulk thermodynamic arguments, these films are metallurgically stable with respect to GaAs up to their melting point. The alloying of silver with gallium results in a substantial reduction in n-type barrier height. Analogous increases in barrier height were observed for contacts to p-type material. Barrier heights as low as 0.59–0.62 eV were measured for annealed ζ-AgGa contacts to n-type material.

Schottky-barrier behavior of copper and copper silicide on n-type and p-type silicon.

The Schottky-barrier heights of Cu and its silicide ${\mathrm{Cu}}_{3}$Si on both n-type and p-type Si(100) have been measured in the temperature range 95--295 K with the use of a current-voltage technique. X-ray photoemission spectroscopy, Rutherford backscattering, and glancing-angle x-ray diffraction were used to monitor the reaction between Cu and Si. Impurity-related energy levels in Si were determined using deep-level transient spectroscopy. Only one level was observed at \ensuremath{\sim}0.55 eV below the conduction-band edge upon copper deposition. Silicide formation was found to cause the disappearance of this level and also to have very little effect on the barrier height and its temperature dependence. For both the metal and the reacted silicide phase, the change in the n-type barrier height with temperature follows closely the change in the indirect energy gap in Si. The p-type barrier height does not exhibit a temperature dependence. These results suggest that the Fermi level at the interface is pinned relative to the valence-band edge. These results deviate from the predictions of models of Schottky-barrier formation based on Fermi-level pinning in the center of the semiconductor indirect band gap. Along with those Schottky barriers reported for metal-Si systems with a wide range in metal electronegativity, the present results show that the barrier height and its temperature dependence are affected by the metal.

Formation, oxidation, electronic, and electrical properties of copper silicides

The solid state reaction between copper and silicon has been studied using Rutherford backscattering, glancing-angle x-ray diffraction, scanning electron microscopy, and x-ray photoemission spectroscopy. Schottky-barrier-height measurements on n-type Si (100) have also been performed in the temperature range of 95–295 K with the use of a current-voltage technique. The results show that a metal-rich compound with a composition in the Cu3Si range forms at low temperatures (473 K). The electronic properties of the compound are dominated by the hybridization between the Cu(d) and Si(p) valence states. A direct consequence of this hybridization is the peculiar oxidation behavior of the compound surface; both Cu and Si have been found to oxidize at room temperature. The oxidation of Si in the silicide is enhanced as compared with the oxidation of the elemental single-crystalline Si surface. Upon annealing the oxidized surface, a solid state reaction takes place: Cu2O disappears and a thicker SiO2 layer grows, owing to the large difference in free energies of formation between SiO2 and Cu2O. The n-type barrier height of 0.79 eV for both the as-deposited metal and the metal-rich silicide phase decreases with increasing temperature with a coefficient close to the temperature coefficient of the indirect energy gap in Si. These results suggest that the Fermi level at the interface is pinned relative to the valence-band edge, independent of temperature.

Vacuum ultraviolet photoelectron spectroscopy of (NH4)2S-treated GaAs (100) surfaces

The surface chemistry and band bending of the ammonium sulfide-treated GaAs (100) surface has been studied using surface-sensitive synchrotron radiation photoemission spectroscopy. We find that the treatment leaves the GaAs surface terminated with roughly a monolayer of sulfur bonded to both As and Ga atoms. An n-type barrier height of 0.8 eV is measured. The thermal stability of the various chemical components is studied and various issues of the passivating mechanism are discussed.