M. N. Pisanias

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...

Transport processes in α-quartz through computer modeling

The charging and discharging processes in a-quartz sandwiched between two blocking contacts are studied by solving numerically the transport equations. Results for the transient current are in good agreement with experiment. The rotation of crystallographic planes upon the application of an electric field is also quantitatively justified through results of the spatial distribution of the electric field.

Interface traps density of anodic porous alumina films of different thicknesses on Si

Impedance Spectroscopy was employed in order to investigate the electrical properties of thin porous anodic alumina films on Si, of thicknesses in the range of 50-200 nm, fabricated by anodization in sulfuric acid. C–V and G–V measurements were performed in the voltage range +5.0 V to −10.0 V and the frequency range 1 MHz to 100 Hz. The typical form of C–V and G–V curves of a metal-insulator-semiconductor (MIS) structure was obtained. The effective dielectric constant e was calculated with a typical value of 6.5, in good agreement with previous published results. C-ω and G-ω measurements were performed as a function of the applied gate voltage in the depletion region in order to calculate the interface trap density Dit and interface trap time constant τit. Dit and τit were evaluated following the conductance method. The evaluated Dit values are of the order of 1012 eV−1 cm−2 and their observed thickness dependence is rather attributed to differences of the porous alumina/p-Si interface, introduced during the formation process, than to sample thickness.

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...

A study on the temperature dependence of the electrical conductivity of a pyrolysed cyano-substituted polyamide derived from 1,4-bis(2-cyano-2-carboxyvinyl)benzene

An unsaturated polyamide with pendant cyano groups was prepared from 1,4-bis(2-cyano-2-carboxy-vinyl)benzene, and its electrical conductivity was studied, as a function of temperature, following pyrolysis at 550, 650 and 700°C. The results show that the unpyrolysed polymer has insulating properties at room temperature, whereas a dramatic increase of the electrical conductivity is observed with increasing pyrolysis temperature, ranging from 6.451 × 10−6 S cm−1 at 550°C to 8.130 × 10−1 S cm−1 at 700°C. The temperature dependence of the electrical conductivity of the pyrolysed polymer suggests that the resulting material has semiconducting properties. The observed electrical conductivity is thermally activated, and may be associated with both intermolecular and intramolecular conduction processes, with activation energies ranging from 0.13 to 0.02 eV for the intermolecular conduction process and from 0.26 to 0.05 eV for the intramolecular process, depending on the pyrolysis temperature that is used.

Transient high-field electrical conduction in evaporated thin potassium iodide films

Transient high-field electrical conduction in evaporated thin potassium iodide films has been studied as a function of the applied voltage at room temperature, covering a time range from microseconds to several hours. The results show that the universal dielectric response is valid separately in three regions. The electrical conduction is achieved through the hopping mechanism. The transition probability, associated with the hopping mechanism in each region, is affected differently by the applied voltage.

Thermosetting resins prepared from the reactions of diaminomaleonitrile with 4,4′-bismaleimidediphenylmethane and electrical conductivity measurements of the resulting materials following pyrolysis

A new series of thermosetting resins were prepared from the reaction of diaminomaleonitrile (DAM) with 4,4′-bismaleimidediphenylmethane (BM) under various molar ratios. The resins were characterized by FT-IR, DTA, TGA and TMA. They had a complex network structure depending on their composition. The DTA studies revealed that their crosslinking started at about 40 °C below the temperature required for crosslinking of BM. Their thermal stability was correlated with their composition and the curing conditions. The cured resins obtained upon curing at 300 °C for 60 h were remarkably more thermally stable than BM which cured itself under the same conditions. They were stable up to 326–377 °C and afforded an anaerobic char yield of 56–72% at 800 °C. Prior to pyrolysis, most of the resins were of amorphous structure, and behaved electrically, at room temperature, as insulators. A decrease of the electrical resistivity was observed with increasing pyrolysis temperature. All resulting conductive materials were of amorphous structure as revealed by their X-ray diffraction profiles. The temperature dependence of the electrical resistivity was measured in the temperature range −173–327 °C (100–600K) for all pyrolysed materials. The results suggest semiconducting properties. The thermally activated conduction model, as well as the variable range hopping model, were applied in order to interpret the experimental data. The observed electrical conductivity seems to be thermally activated and could be associated with intermolecular and intramolecular hopping conduction processes. The activation energies for the intermolecular process ranges from 0.249 to 0.018 and 0.387 to 0.059 eV for the intramolecular process depending on the pyrolysis temperature. The electrical behaviour of all conductive materials could be easily controlled from insulating to semiconducting by controlling both the pyrolysis temperature and duration. The highest electrical conductivity of 1.98 × 101 S cm−1 was observed for a conductive material pyrolysed at 800 °C for 40 h.

Correlation between infrared transmission spectra and the interface trap density of SiO2 films

This work is an attempt to estimate the electrical properties of SiO 2 thin films by recording and analyzing their infrared transmission spectra. In order to study a big variety of films having different infrared and electrical properties, we studied SiO 2 films prepared by low pressure chemical vapor deposition (LPCVD) from SiH 4 + O 2 mixtures at 425 °C and annealed at 750 °C and 950 °C for 30 min. In addition thermally grown gate quality SiO 2 films of similar thickness were studied in order to compare their infrared and electrical properties with the LPCVD oxides. It was found that all studied SiO 2 films have two groups of Si-O-Si bridges. The first group corresponds to bridges located in the bulk of the film and far away from the interfaces, the grain boundaries and defects and the second group corresponds to all other bridges located near the interfaces, the grain boundaries and defects. The relative population of the bulk over the boundary bridges was found equal to 0.60 for the LPCVD film after deposition and increased to 4.0 for the LPCVD films after annealing at 950 °C. Thermally grown SiO 2 films at 950 °C were found to have a relative population of Si-O-Si bridges equal to 3.9. The interface trap density of the LPCVD film after deposition was found equal to 5.47 x 10 12 eV -1 cm -2 and decreases to 6.50 × 10 10 eV -1 cm -2 after annealing at 950 °C for 30 min. The interface trap density of the thermally grown film was found equal to 1.27 x 10 11 eV -1 cm -2 showing that films with similar Si-O-Si bridge populations calculated from the FTIR analysis have similar interface trap densities.

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.

Thin porous anodic alumina films: Interface trap density determination

The electrical properties of thin porous alumina films in the form of MOS structures were studied with dielectric spectroscopy at room temperature. The thickness of the samples was found to be approximately 95 nm with a cross section area of 1.6×10−3 cm2.C-V andG-V measurements were performed by applying a loop sweep voltage 2.0 V to −5.0 V. Correction to the measurements were performed by considering a series resistanceRS and leakage currentIDC.TheC-V results show hysteresis effects due to the presence of positive charges in porous alumina. These charges may be are attributed to the residual electrolyte during the anodization process in the sample preparation. Three distinct regions in theC-V results are observed, namely the inversion, the depletion and the accumulation regions. In the voltage region, where depletion of carriers is observed,C-f andG-f measurements were recorded in the frequency range 1 Hz to 106 Hz. The conductance method was applied for the calculation of the density Dit of carriers, trapped in the interface between insulator and semiconductor, and of the response time τit as a function of the applied bias voltage were performed. The values obtained for Dit and τit are of the order of 3×1012 eV−1 cm−2 and 10−3 s, respectively, and they are voltage dependent.