F. Cardon

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.

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.

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...

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.

On the relationship between interfacial defects and Schottky barrier height in Ag, Au, and Al/n‐GaAs contacts

The variation of the Schottky barrier height in Ag, Au, and Al/n‐GaAs contacts has been investigated as a function of the annealing temperature of the GaAs substrate. Angle resolved x‐ray photoemission spectroscopy measurements show that the substrate surface changes from As‐rich into Ga‐rich over the applied annealing range. Two distinct barrier heights (about 0.85 and 0.65 eV) are found, depending on the metal and the annealing temperature. These values correspond to the Fermi level pinning positions expected for amphoteric defect reactions involving the AsGa and GaAs antisites, respectively. Changes in the barrier height are found at annealing temperatures associated with the removal of these defects.

An XPS study of the dopants' valence states and the composition of CaS1 − xSex:Eu and SrS1 − xSex:Ce thin film electroluminescent devices

Abstract X-ray photoelectron spectroscopy (XPS) was performed on CaS 1 − x Se x :Eu and SrS 1 − x Se x :Ce electroluminescent structures, in order to examine the composition and stoichiometry of the different layers in the thin film stack. The positive effect of selenium coevaporation on the quality of the active layer was clearly established. A detailed XPS study of the valences of europium and cerium doping elements, incorporated in the CaS 1 − x Se x and SrS 1 − x Se x host lattice, was completed. It was shown that Ce is in a 3 + state. The Eu valence determination was not as straightforward since divalent europium does not remain stable during the XPS measurements. The impact of aging on the electroluminescent emission and on the chemical state of the rare earth dopants was also studied.

The influence of a HF and an annealing treatment on the barrier height of p- and n-type Si MIS structures

In this paper, the influence of two pre-evaporation surface treatments on the electrical characteristics of n- and p-Si/Au, Cr and Ti MIS diodes are studied. A strong dependence of the barrier height on the pre-evaporation treatment is observed and is found to be independent of the metal work function. In order to explain this, it is suggested that the interfacial charges are strongly affected by the pre-evaporation treatment used.

CoSi2 formation in the Ti/Co/SiO2/Si system

Cobalt silicide formation has been studied in the presence of a thin, chemically grown interfacial SiO2 and a Ti capping layer. It is found that for ex situ annealing without a capping layer (Co/SiO2/Si system), no silicide is formed. In the presence of a Ti capping layer (Ti/Co/SiO2/Si system), CoSi is formed, followed by CoSi2 at higher temperature. The CoSi formation temperature is dependent on the capping layer thickness. The reaction mechanism has been studied in detail. It is found that the function of the Ti capping layer is twofold: first of all the capping layer protects the silicidation reaction from oxygen contamination. Second, Ti from the cap is able to diffuse through the unreacted Co and to transform the interfacial SiO2 diffusion barrier into a CoxTiyOz diffusion membrane. The CoSi2 layer has a preferential epitaxial orientation with the (100) silicon substrate. The epitaxial quality is dependent on the annealing temperature and the thickness of the Co and Ti layers. It is shown that CoSi2...