N. Xanthopoulos

Transient and ac electrical transport under forward and reverse bias conditions in aluminum/porous silicon∕p-cSi structures

Dielectric impedance measurements as well as transient current–voltage (I–V) characteristics under conditions of forward and reverse bias are reported in aluminum/porous silicon (PS)∕p-cSi structures at different temperatures. Under reverse bias conditions, the electrical conduction of the structures can be modeled by a simple equivalent circuit of two parallel RC networks in series combination, representing a bulk and a junction region. The bulk conduction is ohmic. From the detailed analysis of the PS/cSi junction, the carrier concentration NA and the depletion layer width W are evaluated at each temperature. The elapsed time t0 from the onset of the square pulse, at which the transition from the dominant bulk resistance to junction conduction takes place, is a function of temperature. As the temperature decreases, conduction due to bulk resistance dominates over junction conduction. On the other, hand forward conduction is dominated from the bulk. Two conduction mechanisms are present. As the time proc...

Dielectric response and ac conductivity analysis of hafnium oxide nanopowder

The dielectric response of hafnium oxide nanopowder was studied in the frequency range of 10−2–106 MHz and in the temperature range of 20–180 °C. Broadband dielectric spectroscopy was applied and the experimental results were analyzed and discussed using the electric modulus (M*) and alternating current (ac) conductivity formalisms. The analyses of the dc conductivity and electric modulus data revealed the presence of mechanisms which are thermally activated, both with almost the same activation energy of 1.01 eV. A fitting procedure involving the superposition of the thermally activated dc conductivity, the universal dielectric responce and the near constant loss terms has been used to describe the frequency evolution of the real part of the specific electrical conductivity. The conductivity master curve was obtained, suggesting that the time–temperature superposition principle applies for the studied system, thus implying that the conductivity mechanisms are temperature independent.

Probing the properties of atomic layer deposited ZrO2 films on p-Germanium substrates

Zirconium oxide (ZrO2) thin films of 5 and 25 nm thickness were deposited by atomic layer deposition at 250 °C on p-type Ge substrates. The stoichiometry, thickness, and valence band electronic structure of the ZrO2 films were investigated by x-ray and ultraviolet photoelectron spectroscopies. For the electrical characterization, metal-oxide-semiconductor (MOS) capacitive structures (Pt/ZrO2/p-Ge) have been fabricated. Capacitance–voltage and conductance–voltage (C–V, G–V) measurements performed by ac impedance spectroscopy in the temperature range from 153 to 313 K reveal a typical MOS behaviour with moderate frequency dispersion at the accumulation region attributed to leakage currents. For the determination of the leakage currents conduction mechanisms, current density–voltage (J–V) measurements were carried out in the whole temperature range.

CuO/Ta2O5 core/shell nanoparticles synthesized in immersed arc-discharge: production conditions and dielectric response

We reported recently on a novel nanostructured material produced by the arc-discharge in water method, and extended studies were realized to identify the nature of this material, i.e., CuO/Ta2O5 core/shell crystalline nanoparticles (NPs). As a continuation of this investigation on the possibility of complex NP synthesis using immersed arc-discharge, the production conditions of the CuO/Ta2O5 NPs are herein presented in detail and the electrical properties of the nanopowder are examined comprehensively. The discharge is thus probed in situ by electrical measurements, optical emission spectroscopy and high speed imaging, and the electrical behavior of the NPs is considered by means of broadband dielectric spectroscopy. This combined study provides an integrated characterization of this new material, unveils its potential applications, and makes available suggestions on the process control.

ZrO2 and Al2O3 Thin Films on Ge(100) Grown by ALD: An XPS Investigation

Thin films of aluminium oxide (Al2O3) and zirconium oxide (ZrO2) were prepared by Atomic Layer Deposition (ALD) on p-type (100) germanium substrates. In the present work a detailed analysis of the films by X-ray photoelectron spectroscopy (XPS) in order to investigate their chemical composition is presented. This study is dedicated to an XPS investigation of the principal core levels (Al, Zr, O) of Al2O3 and ZrO2 thin films. In particular, wide scan spectra, detailed scans for the Zr 3d, Al 2p, O 1s, and C 1s regions and related data for zirconia and alumina films are presented and discussed. The results point out the formation of Al2O3 and ZrO2 films with the presence of OH groups and carbon contamination on the surface.

Transient and alternating current conductivity of nanocrystalline porous alumina thin films on silicon, with embedded silicon nanocrystals

Structural characterization and surface topography of porous alumina thin films on silicon with embedded silicon nanocrystals were performed using scanning and transmission electron microscopy. The nature of porous alumina thin films is nanocrystalline with a high density of uniformly distributed silicon nanocrystals. The pores were randomly distributed with an average size of 35 nm. ac impedance spectroscopy measurements were performed at room temperature, from 0.05 up to 3.0 V in the range of 1–105 Hz for both porous alumina thin films with and without embedded silicon nanocrystals. Transient current measurements were also performed from 0.5 up to 50.0 V in the time interval 1–100 s both in forward and reverse bias conditions. The electrical conduction is dominated by the porous alumina matrix and there is no evidence of participation of the contacts to the electrical properties of the thin films. ac conductivity results follow the dielectric universal response through the whole frequency range of inves...

Temperature dependence of the transient and AC electrical conductivity of porous silicon thin films

Abstract In order to investigate the prevailing conduction mechanisms of porous silicon (PS) thin films AC impedance spectroscopy measurements, as well as transient current measurements, as a function of voltage, were performed in the temperature range from 170 to 350 K. The frequency span was 1 Hz up to 1 MHz and the time range 5×10 −5 –10 s. The analysis of the experimental results involved correlation between AC and transient conductivity. The AC and transient conductivity measurements obey the Power Law of Dielectric Universal Response. The analysis shows that, within the range of the frequency span and time range of the measurements, the electrical conductivity is governed by three conduction mechanisms: In the low temperature region, specifically from 170 to 230 K, tunneling is the prevailing conduction mechanism. In the temperature range from 230 to 350 K two more thermally activated mechanisms contribute to the conductivity of PS thin films. The Ohmic conduction mechanism follows tunneling and precedes the Poole–Frenkel conduction mechanism. The time interval within each of these mechanisms is the prevailing one depends on temperature and applied voltage. The activation energy of Ohmic conduction as well as the exponential factor of Poole–Frenkel mechanism have been calculated.

Electrical characteristics of Al 2 O 3 and Ta 2 O 5 nanoparticles synthesized by DC anodic ARC-discharge in water

Because of the length scale and high specific surface area of nanometer-sized particles, they exhibit novel properties as compared with their bulk counterpart materials. Furthermore, the incorporation of well-characterized nanoparticles in various organic matrices provides dielectrics with improved electrical, mechanical and thermal features. Alumina and tantalum-pentoxide nanoparticles have been proved efficient fillers in such nanocomposites. These specific particles are herein produced by DC anodic arc-discharge immersed in water and they are probed by means of broadband dielectric spectroscopy in a wide temperature range (-100 to 100 °C). Different formalisms (effective dielectric constant, loss factor and specific conductivity) are combined, providing the possibility to determine the frequency and temperature dependence of the dielectric characteristics of the synthesized nanoparticles. The knowledge of the latter should be determinant for potential application of alumina and tantalum-pentoxide fillers to two-phase heterogeneous nanodielectrics.

A study on the AC and transient electrical conduction in evaporated thin potassium iodide films

The AC conduction in thin potassium iodide films in the range 5 Hz to 20 kHz has been studied for applied voltages between 0.4 and 1.2 V at room temperature. The universal dielectric response sigma =b omega n for AC conductivity is obeyed for all the applied voltages. Taking into consideration the linearity in the AC conductivity and the nature of the potassium iodide films, previous results on the transient electrical conductivity of thin potassium iodide films are analysed and resolved into two components, one of which is associated with ionic conductivity and the other with the Poole-Frenkel effect.

Influence of the atomic layer deposition temperature on the structural and electrical properties of Al/Al2O3/p-Ge MOS structures

The influence of deposition temperature on the structural, chemical, and electrical properties of atomic layer deposition (ALD)-Al2O3 thin films is investigated. ALD-Al2O3 films were deposited on p-type Ge substrates at 80, 150, 200, 250, and 300 °C. The atomic force microscopy analysis reveals smooth and cohesive films with extremely low roughness (0.2–0.6) nm at 150, 200, 250, and 300 °C. On the contrary, Al2O3 films deposited at the lowest available deposition temperature (80 °C) exhibit holes and aggregates implying a nonhomogeneous deposition. The x-ray photoelectron spectroscopy (XPS) analysis indicates the presence of stoichiometric Al2O3 films at all deposition temperatures. The calculated thickness from the analysis of XPS spectra seems to be in good agreement with the ALD nominal thickness for the films deposited at all deposition temperatures except the one of 80 °C. Transmission electron microscopy (TEM) analysis reveals a flat interface between Al2O3 and p-Ge in an atomic level. In addition, ...