R.L. Van Meirhaeghe

On the difference in apparent barrier height as obtained from capacitance-voltage and current-voltage-temperature measurements on Al/p-InP Schottky barriers

Abstract The difference in apparent barrier height as obtained from capacitance-voltage and current-voltage measurements on Al/ p -InP Schottky barriers was explained by introducing a distribution of barrier heights over the contact area and a temperature dependence of the real barrier height. Taking into account this barrier height distribution and the temperature dependence of the barrier height, we were also able to explain the measured values of the effective Richardson constant. As a result a modified expression for the temperature dependence of the current-voltage characteristics was obtained.

Determination of tunnelling parameters in ultra-thin oxide layer poly-Si/SiO2/Si structures

Abstract In this work the electron tunnelling in device grade ultra-thin 3–6 nm n + poly-Si/SiO 2 /n-Si structures has been analysed. The well known analytic expression for the Fowler-Nordheim tunnelling current was adapted to include the case of direct tunnelling of electrons, which becomes important for oxide layers thinner than 4.5 nm. For these ultra-thin oxide MOS structures it is necessary to take the band bending in the Si substrate and in the poly-Si layer into account to determine the oxide electrical field strength and to derive the tunnelling parameters of the measured current-voltage characteristic. A method is explained to derive the tunnel barrier height φ s and the effective mass of the tunnelling electron m ox from the experimental tunnel current characteristics. It is shown that both the direct tunnelling and the Fowler-Nordheim tunnelling current can be quantitatively explained by a WKB approximation using m ox as the single fitting parameter.

Electrical characteristics of Al/SiO2/n-Si tunnel diodes with an oxide layer grown by rapid thermal oxidation

Abstract Ultrathin oxide layers, 2– nm thick, have been grown on (100) n-Si by Rapid Thermal Oxidation (RTO) at 900°C. RTO is an effective method to control the oxide thickness in this range to within 10%. The direct tunnelling through these ultrathin layers is examined with current-voltage and impedance measurements on Al/SiO2/n-Si structures with an oxide layer thickness between 2 and 4 nm. After the determination of the surface potential vs bias relation and the oxide layer capacitance from the capacitance-voltage measurements, a quantitative analysis of the current-voltage characteristic based on electron tunnelling from a degenerate accumulation layer through the SiO2 barrier into the metal is made. A very good agreement with the theory is obtained assuming a simple trapezoidal tunnel barrier for the SiO2, from which the tunnel barrier height and the electron effective mass in the SiO2 bandgap are derived. The density of interface traps at the Si/SiO2 interface is determined using the conductance method. Only a very small increase of interface trap density with decreasing oxide layer thickness is found. The very high density of interface traps (more than 3 × 1012 cm−2 eV−1) can be reduced to the 1010 cm−2 eV−1 level by application of a conventional Post Metallization Anneal (PMA).

Influence of defect passivation by hydrogen on the Schottky barrier height of GaAs and InP contacts

The change in barrier height caused by sputter metallization of contacts on both GaAs and InP substrates, and using evaporated contacts as a reference, is investigated. It has been found that by annealing, the reference barrier height can be restored. A model is proposed, wherein sputter metallization leads to passivation of interfacial defects by hydrogen. Accordingly, the Fermi level pinning caused by these defects is removed and the barrier height changes and is determined by other mechanisms. Annealing produces a removal of hydrogen and reactivates the amphoteric defects. Additional evidence is given for the assumption that sputter metallization leads to passivation, by hydrogen, of dopants and defects in the semiconductor.

High-temperature degradation of NiSi films: Agglomeration versus NiSi2 nucleation

The thermodynamical and morphological stability of NiSi thin films has been investigated for layers of thickness ranging from 10to60nm formed on either silicon-on-insulator (SOI), polycrystalline silicon, or preannealed polycrystalline silicon substrates. The stability of the films was evaluated using in situ x-ray-diffraction, sheet resistance, and laser light-scattering measurements. For NiSi films that are thinner than 20nm, agglomeration is the main degradation mechanism. For thicker films, the agglomeration of NiSi and nucleation of NiSi2 occur simultaneously, and both degradation mechanisms influence each other. Significant differences were observed in the degradation of the NiSi formed on different substrates. Surprisingly, agglomeration is worse on SOI substrates than on poly-Si substrates, suggesting that the texture of the NiSi film plays an important role in the agglomeration process. As expected, preannealing of the polycrystalline silicon substrate prior to metal deposition results in a signi...

A ballistic electron emission microscopy study of barrier height inhomogeneities introduced in Au/III-V semiconductor Schottky barrier contacts by chemical pretreatments.

The distribution of Schottky barrier heights over the contact area in Au/III-V semiconductor (GaAs, InP, AlxGa1-xAs, InxGa1-xAs) diodes was determined using ballistic electron emission microscopy. Samples which received a chemical pretreatment in aqueous HF or HCl solutions showed changes in the barrier height distribution. In some cases, short rinses in deionized water could remove these effects. Additional XPS measurements and our former work on Si enabled us to propose a model wherein negatively charged species containing F or Cl at the interface are assumed to be responsible for these changes in barrier height distribution. However, in some cases, these effects were shadowed by more drastic influences due to the chemical processing such as changes in the stoichiometry of the surface region.

Current‐voltage characteristic of Ti‐pSi metal‐oxide‐semiconductor diodes

The electrical characteristics of Ti‐pSi metal‐oxide‐semiconductor diodes have been studied as a function of temperature and of applied voltage, using conventional Schottky barrier capacitance‐voltage (C‐V) and current‐voltage (I‐V) measurements. The results show a strong deviation from those expected from thermionic emission and from the minority carrier injection theory for the current mechanism. Unlike other authors who proposed a multistep recombination‐tunneling mechanism, we have stressed that a model based on the inhomogeneity of the barrier height over the diode area predicts a temperature and voltage behavior of the I‐V characteristic similar to the recombination‐tunneling mechanism. The concept of inhomogeneity proposed by former authors is supported by Auger depth concentration profiles which show an intermixed region of Ti and Si. It is observed that the equilibrium semiconductor band bending exhibits a stronger temperature dependence than expected from the variation of the semiconductor Fermi...

In situ x-ray diffraction study of metal induced crystallization of amorphous germanium

Metal induced crystallization (MIC) is a technique that lowers the crystallization temperature of amorphous semiconductors. The process has mainly been used to influence the crystallization of amorphous silicon (a-Si) and multiple studies on this subject have already been performed. The research of the MIC of amorphous Ge (a-Ge) has been mostly limited to the use of a Ni or Al film. This paper focuses on the characterization of the crystallization behavior of a-Ge films in the presence of 20 transition metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, and Al). The kinetics of the crystallization process are also systematically studied for the seven metals that lower the initial crystallization temperature the most. In addition, the influence of the thickness of the metal film was determined for the case of a Au and Al film. A comparison of the influence of the various metals on a-Ge and a-Si is made and the similarities and differences are discussed using existing models for the MIC process.

A detailed XPS study of the rare earth compounds EuS and EuF3

Abstract Eus and EuF 3 powder samples have been the subject of an extensive XPS study. For both compounds, the valence state of Eu was examined, together with its stability, with respect to X-ray dose, total exposure time under XPS ambient (UHV) and XPS sputter time. Maximum likelihood common factor analysis (MLCFA) has been applied in combination with XPS sputter profiling to determine the correct number of chemical states present in the sample. In this context, the mixed-valence behaviour of Eu in these compounds is discussed. Furthermore, an explanation for the XPS final state effects in the Eu3d, Eu4d and Eu4f photoionisation process is proposed.

Ballistic electron emission microscopy study of barrier height inhomogeneities introduced in Au/n-Si Schottky contacts by a HF pretreatment

The distribution of Schottky barrier heights over the contact area in Au/n-Si diodes was determined by ballistic electron emission microscopy. For samples on which an aqueous HF pretreatment of the Si substrate was applied, the histogram contains several high barrier Gaussian distribution components. After a short rinse, in de-ionized water or methanol, it was mainly the most important lower Gaussian component which was left. Using additional x-ray photoemission spectroscopy and atomic force microscopy measurements allowed us to propose a model, wherein negatively charged species containing F at the interface, are thought to be responsible for the high barrier Gaussian components.