Conductance-voltage Measurements Research Articles

The Main Electrical and Interfacial Properties of Benzotriazole and Fluorene Based Organic Devices

Electrical and interfacial properties of ITO/PEDOT:PSS/poly((9,9-dioctylfluorene)-2,7-diyl(2-dodecyl-benzo[1,2,3]triazole)) (PFTBT)/Au devices were investigated using current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/w-V) measurements at room temperature. The forward and reverse C-V and G/w-V measurements were carried out in the frequency range of 10 kHz-1MHz. The electrical parameters, barrier height (ΦBo ) and ideality factor (n) obtained from the forward bias LnI-V plot were found as 0.711 eV and 3.8, respectively. In addition, the series resistance (Rs ) was obtained using Norde and Cheung's methods; Rs were found as 19.052kΩ and 19.267kΩ, respectively. The experimental C-V and G/w-V characteristics of these structures at various gate biases show fairly large frequency dispersion especially at low frequencies and applied voltage due to interface states (Nss) in equilibrium with the conjugated copolymer, interfacial polymer and Rs . These observations indicate that at low frequencies, the charges at interface states can easily follow an AC signal and yield an excess capacitance and conductance. On the other hand, the values of Nss were determined using high-low frequency capacitance (CLF -CHF ) method and Nss are of order 1011 eV-1 cm−2 which is closer to the values obtained by Hill-Coleman method. Experimental results show that both Nss and Rs values should be taken into account in determining frequency and voltage dependent I-V, C-V and G/w-V characteristics for an organic structure.

Surface passivation for ultrathin Al2O3 layers grown at low temperature by thermal atomic layer deposition

AbstractThin layers of Al2O3 with thickness tox ≤ 8 nm were grown by thermal atomic layer deposition at low temperature of 100 °C and applied to achieve functional surface passivation of crystalline silicon substrates. Measurements of the effective lifetime were performed to characterize the surface passivation effect. Lifetime values in the range of 0.5 ms were obtained for Al2O3 films with tox ≥ 6 nm upon post‐deposition annealing (PDA) at 250 °C in N2 atmosphere. However, when the thickness of the Al2O3 films was reduced to 4 nm, lifetime values well below 0.1 ms were observed even after PDA. Combined capacitance–voltage and conductance–voltage measurements were carried out to extract the amount of charges located near the silicon‐oxide interface and the density of electrically active interface states, respectively. The results of the electrical characterization were used to elucidate the intimate physical mechanisms that govern charge recombination at the Al2O3/Si interface.Density of interface states (a) and lifetime (b) values are reported as a function of the PDA temperature for Al2O3 films of three different thickness values: 4, 6, and 8 nm. magnified image

Effects of interface states and series resistance on electrical properties of Al/nanostructure CdO/p-GaAs diode

The nanostructure CdO thin film was grown on p-GaAs substrate by the sol–gel method. Electrical characterization of Al/CdO/p-GaAs diode was performed using current–voltage and capacitance–conductance–voltage measurements. The ideality factor and barrier height values of the diode were obtained to be 2.29 and 0.62eV, respectively. The energy distribution profiles of interface states were determined by means of Hill–Coleman method. The obtained results revealed that the series resistance and interface states have an important effect on electrical characteristics of Al/CdO/p-GaAs diode.

Schottky barrier diode parameters of Ag/MgPc/p-Si structure

An Ag /Pc/p- Si Schottky barrier (SB) diode was fabricated. The current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G-V) measurements were carried out to determine the characteristic parameters such as barrier height, ideality factor and series resistance of the SB diode. The non-linear behavior of ln (I) vs. ln (V) and ln (I/V) vs. V1/2 plots indicated that the thermoionic emission theory can be applied to evaluate junction parameters for the investigated SB diode rather than space-charge limited conduction (SCLC) mechanism and bulk-limited Poole–Frenkel emission. The bulk doping concentration NB and fixed oxide charges Nf was determined from the measured high frequency C-V curve and was found to be 9.5 × 1014 cm-3 and 2.3 × 1013 cm-2, respectively. The values of barrier height obtained from Norde's function were compared with those from the forward bias current-voltage characteristic, and it was seen that there was a good agreement between barrier heights from both methods.

Size dependent charge storage characteristics of MBE grown Ge nanocrystals on surface oxidized Si

We have demonstrated the growth of size controlled Ge nanocrystals by molecular beam epitaxy on oxidized Si for the fabrication of floating gate memory structure. The size and density of the nanocrystals have been controlled by varying the growth temperature. The role of interface states and nanocrystals on the memory characteristics has been studied using frequency dependent conductance-voltage measurements. Superior retention characteristics and an enhanced memory window width have been achieved by replacing SiO2 with high-k Al2O3 as a blocking oxide with a higher barrier height.

Experimental evidence for the correlation between the weak inversion hump and near midgap states in dielectric/InGaAs interfaces

Temperature dependent capacitance–voltage (C-V) and conductance-voltage (G-V) measurements were performed to obtain activation energies (EA) for weak inversion C-V humps and parallel conductance peaks in Al2O3/InGaAs and Si3N4/InGaAs gate stacks. Values of 0.48 eV (slightly more than half of the band gap of the studied In0.53Ga0.47As) were obtained for EA of both phenomena for both gate dielectrics studied. This indicates an universal InGaAs behavior and shows that both phenomena are due to generation-recombination of minority carriers through near midgap located interface states. The C-V hump correlates with the interface states density (Dit) and can be used as a characterization tool for dielectric/InGaAs systems.

The effect of gamma irradiation on electrical and dielectric properties of organic-based Schottky barrier diodes (SBDs) at room temperature

The effect of 60Co (γ-ray) irradiation on the electrical and dielectric properties of Au/Polyvinyl Alcohol (Ni,Zn-doped)/n-Si Schottky barrier diodes (SBDs) has been investigated by using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at room temperature and 1 MHz. The real capacitance and conductance values were obtained by eliminating series resistance (Rs) effect in the measured capacitance (Cm) and conductance (Gm) values through correction. The experimental values of the dielectric constant (ε′), dielectric loss (ε″), loss tangent (tanδ), ac electrical conductivity (σac) and the real (M′) and imaginary (M″) parts of the electrical modulus were found to be strong functions of radiation and applied bias voltage, especially in the depletion and accumulation regions. In addition, the density distribution of interface states (Nss) profile was obtained using the high-low frequency capacitance (CHF–CLF) method for before and after irradiation. The Nss-V plots give two distinct peaks for both cases, namely before radiation and after radiation, and those peaks correspond to two different localized interface states regions at M/S interface. The changes in the dielectric properties in the depletion and accumulation regions stem especially from the restructuring and reordering of the charges at interface states and surface polarization whereas those in the accumulation region are caused by series resistance effect.

Analysis of the minority carrier response of n-type and p-type Au/Ni/Al2O3/In0.53Ga0.47As/InP capacitors following an optimized (NH4)2S treatment

The electrical properties of metal-oxide-semiconductor capacitors incorporating atomic layer deposited Al2O3 on n-type and p-type In0.53Ga0.47As were investigated. A clear minority carrier response was observed for both n-type and p-type Au/Ni/Al2O3/In0.53Ga0.47As devices following an optimized ammonium sulfide (NH4)2S treatment. Capacitance-voltage and conductance-voltage measurements performed at varying temperatures allowed an Arrhenius extraction of activation energies for the minority carrier response, indicating a transition from a generation-recombination regime to a diffusion controlled response.

Elimination of the weak inversion hump in Si3N4/InGaAs (001) gate stacks using an in situ NH3 pre-treatment

Silicon nitride thin films were deposited by plasma enhanced chemical vapor deposition on In0.53Ga0.47As (001) surfaces with and without NH3 pre-deposition treatments. The influence of the NH3 pre-deposition treatments on the electrical properties of the Si3N4/In0.53Ga0.47As interface was investigated by frequency dependent capacitance-voltage and conductance-voltage measurements. A fully unpinned C-V behavior was obtained for all samples. Samples that underwent NH3 pre-deposition treatment exhibited electrical characteristics with no evidence of the midgap interface states (Dit) effects in weak inversion, which are reported in the literature on In0.53Ga0.47As capacitors.

Preparation and dielectric properties of polyvinyl alcohol (Co, Zn Acetate) Fiber/n-Si and polyvinyl alcohol (Ni, Zn Acetate)/n-Si Schottky diodes

Dielectric properties and ac electrical conductivity (σac) of Au/PVA(Co, Zn acetate)/n-Si and Au/PVA(Ni, Zn acetate)/n-Si Schottky diodes (SDs) have been investigated in dark and under illumination by using experimental capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at 1 MHz and room temperature. Experimental results indicate that the change in dielectric constant (ɛ′), dielectric loss (ɛ″), loss tangent (tanδ), the real (M′) and imaginary (M″) parts of electric modulus and ac electrical conductivity (σac) with illumination were found to change linearly with illumination level (P). On the other hand, the ɛ′, ɛ″, tanδ and σac vs P have positive slope while the M′ and M″ vs P have negative slope. Such behavior of dielectric properties and σac can be attributed to illumination induced electron-hole pairs under illumination effect in the depletion region of SDs. The obtained results under illumination suggest that these devices can be used as a sensor in optical applications.

Single- and Dual-Layer Nanocrystalline Indium Tin Oxide Embedded ZrHfO High-k Films for Nonvolatile Memories – Material and Electrical Properties

MOS capacitors composed of singe- and dual-layer nc-ITO embedded ZrHfO high-k gate dielectric stacks were fabricated and characterized for nonvolatile memory functions. Detailed material and electrical properties such as charge-trapping and -detrapping characteristics have been investigated. The XPS analysis indicates the formation of an interface layer at the nc-ITO and ZrHfO contact region. The memory function of this kind of device is mainly based on trapping holes at both bulk nc-ITO sites and nc-ITO/ZrHfO interfaces. By including the second nc-ITO layer into the nc-ITO embedded high-k dielectric stack, the capacitor showed a larger hole-trapping density, a higher data-programming efficiency, and a longer charge retention time. The frequency-dependent capacitance-voltage and conductance-voltage measurement results showed that part of the trapped holes were loosely retained at the nc-ITO/ZrHfO interface. These loosely-trapped holes are responsible for the peak formation in the J-V curve. The long life of the nc-ITO embedded ZrHfO sample makes it suitable for the future nonvolatile memories.

Ruthenium Modified Zr-Doped HfO2 High-k Thin Films with Low Equivalent Oxide Thickness

Thin Zr-doped HfO2 high-k thin film with an equivalent oxide thickness less than 2 nm has been prepared by including ruthenium into the structure. In addition to forming discrete ruthenium nanoparticles in the amorphous Zr-doped HfO2 film, the bulk and interfacial properties, e.g., density of oxygen vacancies and layer composition, were changed with the addition of ruthenium. The permittivity of the film was increased due to the dipole enhancement, which was supported from the frequency-dependent capacitance-voltage and the conductance-voltage measurements change. The ruthenium modified ZrHfO film has a leakage current density 5 orders of magnitude lower than that of the thermally grown SiO2 with the same equivalent oxide thickness. The Schottky emission mechanism was observed in the low electric field regime while the Frenkel-Poole conduction mechanism was applicable in the high electric field regime. A 10-year life expectance is estimated at the gate voltage of 2 V.

Effect of Vanadium Substitution on the Dielectric Properties of Glass Ceramic Bi-2212 Superconductor

Glass ceramic superconductors were prepared by the melt-quenching method. The frequency and temperature dependence of dielectric constant (e′), dielectric loss (e″) and loss tangent (tan δ) of these superconductors were investigated in the frequency range of 10 kHz–10 MHz and temperature range of 80–300 K using the capacitance–voltage (C–V) and conductance-voltage (G/w-V) measurements. Effect of vanadium on bulk properties, dc electrical resistivity (ρ) and ac electrical conductivity (σ ac) of these superconductors were also investigated. The experimental results showed that e′,e″ and σ ac were strongly temperature and frequency dependent. Negative capacitance (NC) phenomenon has been observed and it is believed that the negative capacitance effect is due to polarization effect. The results can be concluded to imply that the interfacial polarization can occur more easily at low frequencies consequently contributing to the deviation of the dielectric properties and ac electrical conductivity of Bi2Sr2Ca1Cu2O δ and Bi1.9V0.1Sr2Ca1Cu2O δ superconductors.

Characterization of CdS and ZnS Nanoparticle Semiconductors: for Optoelectronics Application

In this work, CdS and ZnS semiconducting colloid nanoparticles coated with organic shell, containing either SO−3 or NH+ 2 groups, were deposited as thin films using the technique of electrostatic self-assembly. The films produced were characterized with UV-vis spectroscopy - for optical properties; mercury probe - for electrical characterisation; and photon counter - for electroluminescence study. UV-vis spectra show a substantial blue shift of the main absorption band of both CdS and ZnS, either in the form of solutions or films, with respect to the bulk materials. The calculation of nanoparticles’ radii yields the value of about 1.8 nm for both CdS and ZnS. Current-voltage (I-V) and capacitance-frequency (C-f) measurements of polyelectrolyte/nanoparticles (CdS or ZnS) films suggest the tunnelling behaviour in the films while capacitance- voltage (C-V) and conductancevoltage (G-V) measurements suggest that these nanoparticles are conductive. The electroluminescence was detected in sandwich structures of (PAH/CdS/PAH)N using a photon counting detector, but not in the case of ZnS films.

Tunnelling and storage of charges in a-SiNx/nc-Si/a-SiNx structures

The a-SiNx/nc-Si/a-SiNx sandwiched structures are fabricated in a plasma enhanced chemical vapour deposition (PECVD) system on n-type Si substrate. The nc-Si layer in thickness of 5 nm is fabricated from hydrogen diluted silane gas by layer-by-layer deposition technique. The thicknesses of tunnel and control SiNx layer are 3 nm and 20 nm, respectively. Conductance-voltage and capacitance-voltage measurements are used to study the charges tunnelling and storage in the sandsiched structures. Distinct frequency-dependent conductance peaks due to charges tunneling into the nc-Si dots and capacitance-voltage hysteresis characteristic due to charges storage in the nc-Si dots are observed in the same sample. The experimental results demonstrate that by controlling the thickness of tunnel and control SiNx layers charges can be loaded onto nc-Si dots via tunnelling and be stored in a-SiNx/nc-Si/a-SiNx structures.

Frequency and temperature dependence of the dielectric and AC electrical conductivity in (Ni/Au)/AlGaN/AlN/GaN heterostructures

The dielectric properties and AC electrical conductivity (σ ac) of the (Ni/Au)/Al 0.22Ga 0.78N/AlN/GaN heterostructures, with and without the SiN x passivation, have been investigated by capacitance–voltage and conductance–voltage measurements in the wide frequency (5kHz–5 MHz) and temperature (80–400 K) range. The experimental values of the dielectric constant (ε′), dielectric loss (ε′′), loss tangent (tan δ), σ ac and the real and imaginary part of the electric modulus ( M′ and M′′) were found to be a strong function of frequency and temperature. A decrease in the values of ε′ and ε′′ was observed, in which they both showed an increase in frequency and temperature. The values of M′ and M′′ increase with increasing frequency and temperature. The σ ac increases with increasing frequency, while it decreases with increasing temperature. It can be concluded, therefore, that the interfacial polarization can occur more easily at low frequencies and temperatures with the number of interface states density located at the metal/semiconductor interface. It contributes to the ε′ and σ ac .

Comparative effects of H+ and Ca2+ on large-conductance Ca2+- and voltage-gated Slo1 K+ channels

Large-conductance Ca2+- and voltage-gated Slo1 BK channels are allosterically activated by depolarization and intracellular ligands such as Ca2+. Of the two high-affinity Ca2+ sensors present in the channel, the RCK1 sensor also mediates H+-dependent activation of the channel. In this study, we examined the comparative mechanisms of the channel activation by Ca2+ and H+. Steady-state macroscopic conductance-voltage measurements as well as single-channel openings at negative voltages where voltage-sensor activation is negligible showed that at respective saturating concentrations Ca2+ is more effective in relative stabilization of the open conformation than H+. Calculations using the Debye-Hückel formulation suggest that small structural changes in the RCK1 sensor, on the order of few angstroms, may accompany the H+-mediated opening of the channel. While the efficacy of H+ in activation of the channel is less than that of Ca2+, H+ more effectively accelerates the activation kinetics when examined at the concentrations equipotent on macroscopic voltage-dependent activation. The RCK1 sensor therefore is capable of transducing the nature of the ligand bound and transmits qualitatively different information to the channel's permeation gate.

Enhancement in tunnel magnetoresistance effect by inserting CoFeB to the tunneling barrier interface in Co2MnSi/MgO/CoFe magnetic tunnel junctions

Tunnel magnetoresistance (TMR) effect was investigated in Co2MnSi/CoFeB(0–2 nm)/MgO/CoFe magnetic tunnel junctions (MTJs). TMR ratio was enhanced by inserting a thin CoFeB layer at the Co2MnSi/MgO interface. The MTJ with CoFeB thickness of 0.5 nm exhibited the highest TMR ratio. From the conductance-voltage measurements for the fabricated MTJs, we infer that the highly spin polarized electron created in Co2MnSi can conserve the polarization through the 0.5-nm-thick CoFeB layer. Furthermore, by insertion of the thin CoFeB layer, the temperature dependence of the TMR ratio was improved because of the suppression of the fluctuation of the magnetic moment at the Co2MnSi/MgO interface.

Electrical properties of metal-oxide-semiconductor structures with low-energy Ge-implanted and annealed thin gate oxides

The electrical characteristics of low-energy (3keV) Ge-implanted and, subsequently, thermal annealed SiO2 layers are investigated through capacitance-voltage (C-V) and conductance-voltage (G-V) measurements of metal-oxide-semiconductor capacitors. Particular emphasis is placed on the properties of such gate oxides for memory applications. Capacitance measurements at flatband voltage before and after the application of constant voltage stress in the accumulation regime indicate that the charge trapping behavior of the devices undergoes a major change after annealing at temperatures higher than 910°C. The latter change is identified as a relocation of Ge atoms mainly toward the upper portion of the oxide with a significant fraction of them leaving the oxide; a finding in harmony with secondary ion mass spectroscopy analysis. The interface trap density (Dit) for the thin (9–12nm) implanted oxides decreases with increasing annealing temperature, approaching at 950°C the Dit levels in the mid-1010eV−1cm−2 range of the nonimplanted samples. At elevated annealing temperatures (>1000°C), the device C-V characteristics are substantially disturbed. In this case, the presence of electrically active Ge atoms at an extended depth in the substrate modifies the intrinsic electrical properties of the n-Si substrate, lending a p-type conductivity character to the device high-frequency C-V curves. Substrate electrical modification is interpreted through a model that takes into account the formation of a SiO2∕Ge-rich-Si∕n-Si system. The SiO2∕Ge-rich-Si interface presents very low Dit levels as revealed by conductance loss characteristics. The present study suggests that a combination of Ge implantation into SiO2 films and thermal annealing may be exploited in damage-free SiGe epitaxial growth technology based on Ge implantation.

Resonant Tunnelling and Storage of Electrons in Si Nanocrystals within a-SiNx/nc-Si/a-SiNx Structures

The a-SiNx/nanocrystalline silicon (nc-Si)/a-SiNx sandwiched structures with asymmetric double-barrier are fabricated in a plasma enhanced chemical vapour deposition (PECVD) system on p-type Si substrates. The nc-Si layer in thickness 5nm is fabricated from a hydrogen-diluted silane gas by the layer-by-layer deposition technique. The thicknesses of tunnel and control SiNx layers are 3nm and 20nm, respectively. Frequency-dependent capacitance spectroscopy is used to study the electron tunnelling and the storage in the sandwiched structures. Distinct frequency-dependent capacitance peaks due to electrons tunnelling into the nc-Si dots and capacitance-voltage (C - V) hysteresis characteristic due to electrons storage in the nc-Si dots are observed with the same sample. Moreover, conductance peaks have also been observed at the same voltage region by conductance-voltage (G - V) measurements. The experimental results demonstrate that electrons can be loaded onto nc-Si dots via resonant tunnelling and can be stored in our a-SiNx/nc-Si/a-SiNx structures.