A study on structural and electrical properties of low dielectric constant SiOC(–H) thin films deposited via PECVD

Low-dielectric constant SiOC(–H) films were deposited on p-type Si(100) substrates using plasma enhanced chemical vapor deposition (PECVD) at different radio frequency (rf) powers. The structural characteristics of the SiOC(–H) films were characterized using Fourier transform infrared spectroscopy (FTIR) in the absorbance mode. The bonding configurations of the SiOC(–H) films remained unchanged upon annealing, showing their good thermal stability. Electrical characteristics of the SiOC(–H) thin films with Al/SiOC(–H)/p-Si(100)/Al metal-insulator-semiconductor (MIS) structures were analyzed using capacitance–voltage (C–V) and conductance–voltage (G/ω–V) at different frequencies. The conductance and the capacitance measurements were used to extract the interface state density in the MIS structures. From the experimental data and the subsequent quasi-static C–V analysis, the energy distribution of interface state density was obtained. The interface state density of the as-deposited and 400 °C annealed MIS structures increased with increasing rf powers, whereas the fixed charge density decreased with increasing rf powers. The interface state densities and their electrical properties of the SiOC(–H) films strongly affected by the radio frequency power.     

Capacitance–voltage and conductance–voltage characteristics of Ag/n-CdO/p-Si MIS structure prepared by sol–gel method

The frequency dependent electrical properties of Ag/n-CdO/p-Si structure has been investigated using capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics in the frequency range 10 kHz–1 MHz in the room temperature. The increase in capacitance at lower frequencies is observed as a signature of interface states. The presence of the interfaces states (N_SS) is also evidenced as a peak in the capacitance–frequency characteristics. Furthermore, the voltage and frequency dependence of series resistance were calculated from the C–V and G/ω–V measurements and plotted as functions of voltage and frequency. The distribution profile of R_S–V gives a peak in the depletion region at low frequencies and disappears with increasing frequencies. The values of interface state densities and series resistance from capacitance–voltage-frequency (C–V-f) and conductance–voltage-frequency (G/ω–V-f) measurements were obtained in the ranges of 1.44×10¹⁶–7.59×10¹² cm^?2 eV^?1 and 341.49–8.77 Ω, respectively. The obtained results show that the C–V-f and G/ω–V-f characteristics confirm that the interface states density (N_SS) and series resistance (R_S) of the diode are important parameters that strongly influence the electrical parameters in Ag/n-CdO/p-Si structures.     

Investigation of current–voltage and capacitance–voltage characteristics of Ag/perylene-monoimide/n-GaAs Schottky diode

Ag/perylene-monoimide(PMI)/n-GaAs Schottky diode was fabricated and the current–voltage (I–V) characteristics at a wide temperature range between 75 and 350 K and also the capacitance–voltage (C–V) characteristics at room temperature for 1 MHz have been analyzed in detail. The measured I–V characteristics exhibit a good rectification behavior at all temperature values. By using standard analysis methods, the ideality factor and the barrier height are deduced from the experimental data and also the variations of these parameters with the temperature are analyzed. In addition, by means of the Cheung and Cheung method, the series resistance and some other electrical properties are calculated for the diode. Finally, capacitance–voltage characteristics of device have been analyzed at the room temperature. From analyzing the capacitance measurements, Schottky barrier height is determined and then compared with the value which calculated from the I–V measurements at room temperature. Also, the concentration of ionized donors, built-in potential and some other parameters of diode are found using C–V characteristics.     

Temperature-dependent current conduction mechanism and charge trapping in Ta2O5 RF-sputtered on GaN

A gallium nitride (GaN) based Metal-Oxide-Semiconductor (MOS) capacitor was fabricated using radio frequency (RF)-sputtered tantalum oxide (Ta₂O₅) as the high-k gate dielectric. Electrical characteristics of this capacitor were evaluated via capacitance–voltage (C–V), current–voltage (I–V), and interface trap density (D_it) measurements with emphasis on the substrate temperature dependence ranging from 25 °C to 200 °C. Charge trapping and conduction mechanism in Ta₂O₅ were investigated. The experimental results suggested that higher substrate temperature rendered higher oxide capacitance, reduced gate leakage current, and lowered mid-gap interface trap density at the expenses of high border traps and high fixed oxide charges. The gate leakage current through Ta₂O₅ was found to obey the Ohm's conduction at lower gate bias and the Poole–Frenkel conduction at higher gate bias.     

On the electroluminescence from evaporated thin gold films

Au films with island structure show a spot-like electroluminescence (EL) under a low dc or ac voltage. I–V characteristics and their relation to the EL, and some EL features were investigated.     

Electrical parameters of Schottky contacts in CaCu3Ti4O12 thin film capacitors

CaCu₃T_i4O₁₂ (CCTO) thin films were grown by pulsed laser deposition on Pt and La_0.9Sr_1.1NiO₄ (LSNO) bottom electrodes. The electrical characteristics of the CCTO/Pt and CCTO/LSNO Schottky junctions have been analyzed by impedance spectroscopy, capacitance–voltage (C–V) and current–voltage (I–V) measurements as a function of frequency (40 Hz–1 MHz) and temperature (300–475 K). Similar results were obtained for the two Schottky diodes. The conduction mechanism through the Schottky junctions was described using a thermionic emission model and the electrical parameters were determined. The strong deviation from the ideal I–V characteristics and the increase in capacitance at low frequency for ?0.5 V bias are in agreement with the presence of traps near the interfaces. Results point toward the important effect of defects generated at the interface by deposition of CCTO.     

Synthesis,characterization and radiation damage studies of high-k dielectric (HfO2) films for MOS device applications

The current trend in miniaturization of metal oxide semiconductor devices needs high-k dielectric materials as gate dielectrics. Among all the high-k dielectric materials, HfO₂ enticed the most attention, and it has already been introduced as a new gate dielectric by the semiconductor industry. High dielectric constant (HfO₂) films (10?nm) were deposited on Si substrates using the e-beam evaporation technique. These samples were characterized by various structural and electrical characterization techniques. Rutherford backscattering spectrometry, X-ray reflectivity, and energy-dispersive X-ray analysis measurements were performed to determine the thickness and stoichiometry of these films. The results obtained from various measurements are found to be consistent with each other. These samples were further characterized by I–V (leakage current) and C–V measurements after depositing suitable metal contacts. A significant decrease in the leakage current and the corresponding increase in device capacitance are observed when these samples were annealed in oxygen atmosphere. Furthermore, we have studied the influence of gamma irradiation on the electrical properties of these films as a function of the irradiation dose. The observed increase in the leakage current accompanied by changes in various other parameters, such as accumulation capacitance, inversion capacitance, flat band voltage, mid-gap voltage, etc., indicates the presence of various types of defects in irradiated samples.     

Analysis of carrier injection,accumulation and transport process of pentacene field effect transistors using a Maxwell–Wagner model

Carrier injection, carrier transport and carrier accumulation are three key process to understand the characteristics of organic field effect transistor (OFET) devices. In our previous studies, we showed the evidence of carrier injection from source electrode by means of optical second harmonic generation (SHG) measurement and capacitance–voltage (C–V) measurements, and explained the FET characteristics using a Maxwell–Wagner model. In this paper, to further clarify the behavior of the carrier transport and hole injection from source electrode, we focused on the hysteresis behavior observed in the current–voltage (I–V) and C–V characteristics of pentacene FETs. Employing the electric field induced SHG (EFISHG) and C–V measurements, we could show that the origin of the hysteresis behavior is caused by holes, which are injected and subsequently trapped in FET channel.     

Asymmetric electrical properties in Pt/Ba0.5Sr0.5Ti0.99Co0.01O3/Nb-doped SrTiO3 capacitors

Ba_0.5Sr_0.5Ti_0.99Co_0.01O₃ (BSTC) thin films have been fabricated with pulsed laser deposition on Nb-doped SrTiO₃ (STN) substrate. In Pt/BSTC/STN capacitor, we systematically investigated the capacitance, leakage current and polarization versus bias voltage characteristics, and found that curves of capacitance versus voltage and leakage current versus voltage were not symmetric, and polarization hysteresis loop exhibited large relaxation of the remnant polarization at negatively poled state. A detailed analysis of capacitance data demonstrated a difference of the built-in voltage between top Pt/BSTC interface (V_b,t=2.5 V) and bottom BSTC/STN interface (V_b,b=1.1 V). Such different built-in voltages lead to the presence of an internal electric field, which results in asymmetric electric characteristics in Pt/BSTC/STN capacitor.     

Optical and current transport properties of CuO/ZnO nanocoral p–n heterostructure hydrothermally synthesized at low temperature

We demonstrate the synthesis and investigate the electrical and optical characteristics of ‘nanocorals’ (NCs) composed of CuO/ZnO grown at low temperature through the hydrothermal approach. High-density CuO nanostructures (NSs) were selectively grown on ZnO nanorods (NRs). The synthesized NCs were used to fabricate p–n heterojunctions that were investigated by the current density–voltage (J–V) and the capacitance–voltage (C–V) techniques. It was found that the NC heterojunctions exhibit a well-defined diode behavior with a threshold voltage of about 1.52 V and relatively high rectification factor of ～760. The detailed forward J–V characteristics revealed that the current transport is controlled by an ohmic behavior for V≤0.15 V, whereas at moderate voltages 1.46≤V<1.5 the current follows a J? α?exp(βV) relationship. At higher voltages (≥1.5 V) the current follows the relation J? α? V ², indicating that the space-charge-limited current mechanism is the dominant current transport. The C–V measurement indicated that the NC diode has an abrupt junction. The grown CuO/ZnO NCs exhibited a broad light absorption range that is covering the UV and the entire visible parts of the spectrum.     

Ferroelectric characteristics of MFIS structure with P(VDF–TrFE)/BaTiO3 nanocomposite as ferroelectric layer

A metal–ferroelectric–insulator–semiconductor (MFIS) structure has been made using poly(vinylidene difluoride–trifluoroethylene)/barium titanate [P(VDF–TrFE)/BaTiO₃] nanocomposite as ferroelectric layer, on silicon/silicon dioxide (Si/SiO₂) substrate. Different concentrations of BaTiO₃ were added to P(VDF–TrFE) polymer using bath sonication method, and the films were prepared using spin coating method. The structure was annealed to 120 °C for 2 h and then the top aluminium electrode was deposited by thermal evaporation method. Capacitance–voltage shows an increase in accumulation capacitance as the BaTiO₃ nanoparticle concentrations increases. Dielectric constant was estimated from the capacitance voltage (C–V) characteristics and found to be changing as the concentration of BaTiO₃ is varied. Polarization–electric field analyses show hysteresis behaviour of the nanocomposite. A comparison of MFIS and metal–ferroelectric–semiconductor structures was done with varying ferroelectric film thicknesses. All these results suggest that this polymer nanocomposite can be a promising material which can be used in non-volatile memory devices.     

Conductive Atomic Force Microscopy (C-AFM) observation of conducting nanofilaments formation in GeSbTe phase change materials

GST (GeSbTe) thin films were deposited on glass substrates by electron beam evaporation; Ni was used as the top and bottom electrodes. The I–V (current–voltage) characteristic of the phase change memory (PCM) cell was measured; results showed an electrical threshold switching characteristic for the sample with a threshold voltage of 3.08 V. The threshold switching is attributed to the formation of conductive filaments in the amorphous matrix. Current-voltage spectra which were obtained by C-AFM show that the GST thin film switching from amorphous to the crystalline phase occurs at 1.51 V. C-AFM was used to fabricate crystalline nanoarrays on the sample surface and examine the electrical properties of arrays. In the I–V measurements by C-AFM, when the applied voltage is higher than threshold voltage, conducting nanofilaments with average sizes of 15–60 nm were formed and crystallized spots with current signals were observed. Different times of I–V spectroscopies were applied on thin films to investigate the electrical properties of films during the phase change process. C-AFM results show that as the times of I–V spectroscopies increased, the morphology of crystallized spots changed from bump to pit; the sizes of conductive nanofilaments and detected current signals increased. These results can be attributed to the energy induced by Joule heating dissipated to surrounding films increases with the increasing times of I–V spectroscopies.     

Effects of oxygen partial pressure on the ferroelectric properties of pulsed laser deposited Ba0.8Sr0.2TiO3 thin films

The Ba_0.8Sr_0.2TiO₃ thin films were grown on the Pt–Si substrate at 700 °C by using a pulsed laser deposition technique at different oxygen partial pressure (PO₂) in the range of 1–20 Pa and their properties were investigated. It is observed that the PO₂ during the deposition plays an important role on the tetragonal distortion ratio, surface morphology, dielectric permittivity, ferroelectric polarization, switching response, and leakage currents of the films. With an increase in PO₂, the in-plane strain for the BST films changes from tensile to compressive. The films grown at 7.5 Pa show the optimum dielectric and ferroelectric properties and also exhibit the good polarization stability. It is assumed that a reasonable compressive strain, increasing the ionic displacement, and thus promotes the in-plane polarization in the field direction, could improve the dielectric permittivity. The butterfly features of the capacitance–voltage (C–V) characteristics and the bell shape curve in polarization current were attributed to the domain reversal process. The effect of pulse amplitude on the polarization reversal behavior of the BST films grown at PO₂ of 7.5 Pa was studied. The peak value of the polarization current shows exponential dependence on the electric field.     

Physical properties of vacuum evaporated CdTe thin films with post-deposition thermal annealing

This paper presents the physical properties of vacuum evaporated CdTe thin films with post-deposition thermal annealing. The thin films of thickness 500 nm were grown on glass and indium tin oxide (ITO) coated glass substrates employing thermal vacuum evaporation technique followed by post-deposition thermal annealing at temperature 450 °C. These films were subjected to the X-ray diffraction (XRD),UV-Vis spectrophotometer, source meter and atomic force microscopy (AFM) for structural, optical, electrical and surface morphological analysis respectively. The X-ray diffraction patterns reveal that the films have zinc-blende structure of single cubic phase with preferred orientation (111) and polycrystalline in nature. The crystallographic and optical parameters are calculated and discussed in brief. The optical band gap is found to be 1.62 eV and 1.52 eV for as-grown and annealed films respectively. The I–V characteristics show that the conductivity is decreased for annealed thin films. The AFM studies reveal that the surface roughness is observed to be increased for thermally annealed films.     

Single-electron tunneling in granular Ag–SiO2films

Current transport properties of thin Ag–SiO₂granular films were studied. In spite of very simple device structures (i.e., just sandwiching the granular film with Al electrodes), clear Coulomb blockade and Coulomb staircase structures were observed in the current–voltage (I–V) characteristics. The observedI–Vcharacteristics were qualitatively explained by a double-barrier and a triple-barrier tunnel-junction model.     

Photo-induced charge transport in SiO2films containing Si nanocrystals

Photo-induced charge transport is reported in metal–insulator–semiconductor structures containing Si nanocrystals produced by ion implantion and annealing. Successive shifts in current–voltage (I–V) and capacitance–voltage (C–V) curves are shown to be induced by ultra-violet (UV) light exposure under no bias. These shifts are shown to be enhanced by the application of a negative bias voltage during illumination. The application of a positive bias voltage during illumination is shown to reverse the direction of the shifts in both the I–V and C–V curves. This behaviour can be explained by charging of the nanocrystals induced by photoionization of electrons and charge movements in the insulator layer.     

Controlling the electrical characteristics of Al/p-Si structures through Bi4Ti3O12 interfacial layer

In this study, the effects of high permittivity interfacial Bi₄Ti₃O₁₂ (BTO) layer deposition on the main electrical parameters; such as barrier height, series resistance, rectifying ratio, interface states and shunt resistance, of Al/p-Si structures are investigated using the current–voltage (I–V) and admittance measurements (capacitance–voltage, C–V and conductance–voltage, G/ω–V) at 1 MHz and room temperature. I–V characteristics revealed that, due to BTO layer deposition, series resistance values that were calculated by both Ohm's law and Cheung's method decreased whereas shunt resistance values increased. Therefore, leakage current value decreased significantly by almost 35 times as a result of high permittivity interfacial BTO layer. Moreover, rectifying ratio was improved through BTO interfacial layer deposition. I–V data indicated that high permittivity interfacial BTO layer also led to an increase in barrier height. Same result was also obtained through C–V data. Obtained results showed that the performance of the device is considerably dependent on high permittivity BTO interfacial layer.     

Characterization of Al/Si junctions on Si(100) wafers with chemical vapor deposition-based sulfur passivation

Chemical vapor deposition-based sulfur passivation using hydrogen sulfide is carried out on both n-type and p-type Si(100) wafers. Al contacts are fabricated on sulfur-passivated Si(100) wafers and the resultant Schottky barriers are characterized with current–voltage (I–V), capacitance–voltage (C–V) and activation-energy methods. Al/S-passivated n-type Si(100) junctions exhibit ohmic behavior with a barrier height of <0.078 eV by the I–V method and significantly lower than 0.08 eV by the activation-energy method. For Al/S-passivated p-type Si(100) junctions, the barrier height is ~0.77 eV by I–V and activation-energy methods and 1.14 eV by the C–V method. The discrepancy between C–V and other methods is explained by image force-induced barrier lowering and edge-leakage current. The I–V behavior of an Al/S-passivated p-type Si(100) junction remains largely unchanged after 300 °C annealing in air. It is also discovered that heating the S-passivated Si(100) wafer before Al deposition significantly improves the thermal stability of an Al/S-passivated n-type Si(100) junction to 500 °C.     

Effect of dimethyl sulfoxide on the electrical properties of PEDOT:PSS/n-Si heterojunction diodes

Effect of dimethyl sulfoxide (DMSO) on the electrical properties of PEDOT:PSS/n-Si heterojunction diodes has been studied. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was deposited on n-type Si wafer using facile process of spin coating. The DMSO content was varied from 0 to 8 vol%. Electrical characterization of these heterojunction diodes as performed using both current–voltage (I–V) and capacitance–voltage (C–V) measurements. All diodes showed rectifying behavior. AFM measurement revealed that the surface became more rough after the DMSO treatment of PEDOT:PSS films. The RMS values were found in the range of 4–6 nm. The resistivity of the PEDOT:PSS films decreased with increase in temperature. The addition of DMSO into PEDOT:PSS solution results in a decrease in resistivity of films by approximately two orders of magnitude. PEDOT:PSS films showed high transmission more than 85% in the entire visible region. Raman spectroscopy indicated effect of the DMSO treatment on the chemical structure of PEDOT chains, suggesting a conformational change of PEDOT chain in the film. An optimal value of DMSO was obtained with 5 vol% content, and it showed the best PEDOT:PSS films properties and good quality heterojunction diodes characteristics with ideality factor of 2.4 and barrier height 0.80 eV.     

Fabrication and characterization of aluminum-doped zinc oxide Schottky diodes on n-GaN

Aluminum-doped zinc oxide (AZO) films were prepared using an electron-beam evaporation system to form Schottky contacts on n-type GaN at depositing temperatures varied from 100 to 400 °C. The current–voltage (I–V) measurements which showed a rectifying characteristic were carried out to deduce the Schottky barrier heights (SBHs) according to the thermionic emission theory. The SBHs were calculated by using a linear curve fit to forward characteristics of ln(I) against V, and have a small alteration around 0.7 eV. Hall-effect measurements were carried out to illuminate the alteration of the SBHs that were mainly affected by the carrier concentration of the AZO films. It has been found that the SBH ascends as the carrier concentration decrease, and the dislocations play an important role on the leakage current of the contacts.