M. O. Aboelfotoh

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, o...

Electrical transport in thin films of copper silicide

Electrical properties of thin films of η’‐Cu3Si phase with a tetragonal crystal structure are reported on. Electrical transport in these films is found to be very sensitive to oxygen exposure. Cu3Si reacts with oxygen at room temperature to form both Si and Cu oxides, resulting in high‐room‐temperature (∼60 μΩu2009cm) and even nonmetallic resistivity. This behavior is contrasted with that of low‐resistivity (∼5 μΩu2009cm at room temperature) Cu3Ge, which is inert in an oxygen environment.

On Schottky barrier inhomogeneities at silicide/silicon interfaces

The Schottky‐barrier heights of several silicides on both n‐ and p‐Si(100) have been measured in the temperature range 77–295 K. The results deviate significantly from the predictions of a recent model based on the assumption of barrier height inhomogeneities at such interfaces. For all these interfaces, the sum of the barrier heights to n‐ and p‐Si(100) is always equal, within the experimental accuracy, to the indirect band gap of Si. Furthermore, the temperature dependence of the barrier height suggests that the Fermi level at these interfaces is pinned relative to the Si valence‐band edge.

Effect of crystal structure on the electrical resistivity of copper‐germanium thin‐film alloys

Resistivity measurements have been performed on Cu‐Ge thin‐film alloys with Ge concentration ranging from 0 to 40 at.u2009% in the temperature range 4.2–300 K. It is found that the dependence of resistivity on Ge concentration is not monotonic. This behavior is correlated to changes observed in the crystal structure of the alloys as the Ge concentration is increased. The resistivity is found to remain remarkably low (typically less than 10 μΩu2009cm at room temperature) over a range of Ge concentration that extends from 25 to 35 at.u2009%, even though above 25 at.u2009% Ge, the alloys consist of the low resistivity e1‐phase of Cu3Ge and of a Ge‐rich solid solution.

Electrical transport properties of Cu3Ge thin films

Resistivity, Hall‐effect, and magnetoresistance measurements have been performed in the temperature range 4.2–300 K on thin films of the e1‐Cu3Ge phase that has a long‐range ordered monoclinic crystal structure. The results show that e1‐Cu3Ge is a metal with a room‐temperature resistivity of ∼6 μΩ cm. The temperature dependence of resistivity follows the Block‐Gruneisen model with a Debye temperature of 240±25 K. The density of charge carriers, which are predominantly holes, is ∼8×1022/cm3 and is independent of temperature and film thickness. The Hall mobility at 4.2 K is ∼ 132 cm2/Vu2009s. The elastic mean free path is found to be ∼1200 A, which is surprisingly large for a metallic compound film. The results show that the residual resistivity is dominated by surface scattering rather than grain‐boundary scattering. An increase in Ge concentration above 25 at.u2009% (but less than 35 at.u2009%) is found to affect the resistivity and Hall mobility, but not the density of charge carriers.

Interaction between copper and point defects in proton‐irradiated silicon

Schottky barrier structures have been formed by the deposition of Cu and Pt on n‐type Si(100) at room temperature. The structures were irradiated by 300 keV protons or 1.3 MeV alpha particles to doses between 109 and 1010 cm−2. Deep level transient spectroscopy measurements performed in the temperature range 80–290 K revealed a new level ∼0.31 eV below the conduction band edge in the proton‐bombarded Cu/Si(100) samples. The level exhibits metastable properties, and reversible cycling of its strength can be accomplished by a procedure where thermal annealing, forward biasing (hole injection), and white light excitation are undertaken. Evidence is presented showing that the level is associated with both Cu and H. Furthermore, the production rate of electrically active defects, e.g., divacancy and vacancy oxygen centers, is found to be substantially lower in the Cu/Si(100) samples compared with Pt/Si(100) samples irradiated under identical conditions. This is attributed to passivation of the irradiation‐indu...