Dominant Current Flow Mechanism Research Articles

Impact of Adsorbed Gases on the Transport Mechanisms in Ge8As2Te13S3 Amorphous Films

It is shown that the gas adsorption in chalcogenide glasses results in modifications of transport mechanisms by the surface, along with formation of surface localized states. A detailed quantitative analysis is made on experimental data taking on glassy thin films of Ge8As2Te13S3, physically grown in vacuum. The measurements of alternating current (AC) conductivity of these films have been carried out in the frequency range from 5 Hz to 13 MHz, in both dry air and its mixture with a controlled concentration of nitrogen dioxide, at different temperatures. It was found that the changes of environmental conditions by applying of even very small (ppm) amounts of toxic gases, e.g. NO2, dramatically influences the AC conductivity spectra. This is due to a sharp increasing of holes concentration in the valence band of an ultrathin layer adjacent to surface, which results in modification of the dominant mechanism of current flow. In a definite frequency range the charge transport by hopping via valence band edge localized states becomes negligible and the mechanism of conductivity via extended states becomes the main until frequencies ω > 105 Hz, at which the mechanism of hopping via localized states in the vicinity of Fermi level becomes predominant.

Structure and morphology of nanoporous zno and dark current‐Voltage characteristics of the glass/(TCO)/zno/poly[2,7‐(9,9‐dioctylfluorene)‐alt‐(5,5'‐bithiophene)/ag structure

ABSTRACTThe hybrid organic‐inorganic structure based on glass/(TCO)/nanoporous ZnO/poly[2,7‐(9,9‐dioctylfluorene)‐alt‐(5,5′‐bithiophene)]/Ag that was prepared by physical deposition has been investigated. The structure of the nanostructured ZnO obtained by magnetron sputtering was confirmed by X‐ray diffractometry (XRD) and energy dispersive X‐ray spectroscopy (EDX). Scanning electron microscopy (SEM) analysis proved the existence of short and interconnected zinc oxide (ZnO) fibers, which form a continuous porous network with pores having an average diameter of 100 nm. Current‐voltage (I‐V) curves of the glass/TCO/ZnO/PF‐BT/Ag hybrid structure are similar to those of typical p‐n junctions and stable until 90°C temperature. According to the I‐V characteristics, the dominant mechanism of current flow is based on the generation‐recombination of carriers in the depletion region at low direct biases and also on the injection of carriers at high biases. The reverse branch of the I‐V characteristic, calculated in log‐log scale, shows one segment with a power coefficient of 3/2 at room temperature. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42415.

Electrical properties of MOS diodes In/TiO2/p-CdTe

In/TiO2/p-CdTe MOS diodes, which have a rectification coefficient of K = 6 × 103 at an external bias of 2 V, are fabricated for the first time by means of the inexpensive spray-pyrolysis method. It is established that tunnel-recombination processes in the MOS structures under investigation for forward and reverse voltages with the participation of levels at an energy depth of 0.25 eV are the dominant current-flow mechanism. The features of the voltage-capacitance characteristics of In/TiO2/p-CdTe MOS diodes testify to a sharp decrease in the resistance of the TiO2 high-resistance layer at forward bias, which is caused by the relation between the energy parameters of components of the MOS structure under investigation.

Analytical subthreshold current and subthreshold swing models of short-channel dual-metal-gate (DMG) fully-depleted recessed-source/drain (Re-S/D) SOI MOSFETs

In this paper, analytical subthreshold current and subthreshold swing models are derived for the short-channel dual-metal-gate (DMG) fully-depleted (FD) recessed-source/ drain (Re-S/D) SOI MOSFETs considering that diffusion is the dominant current flow mechanism in subthreshold regime of the device operation. The two-dimensional (2D) channel potential is derived in terms of back surface potential and other device parameters. The so called virtual cathode potential in term of the minimum of back surface potential is also derived from 2D channel potential. The virtual cathode potential based subthreshold current and surface potential based subthreshold swing model results are extensively analyzed for various device parameters like the oxide and silicon thicknesses, thickness of source/drain extension in the BOX, control to screen gate length ratio and channel length. The numerical simulation results obtained from ATLAS $$^{\text{ TM }}$$ TM , a 2D numerical device simulator from SILVACO Inc have been used as a tool to verify the model results.

Electrical properties of isotype heterojunctions n-TiN/n-Si

Titanium nitride and silicon are promising materials for use in various photoelectric devices due to their physical properties, so the research of the isotype heterojunctions n-TiN/n-Si is of considerable interest. The article studies the electrical properties of the heterojunctions formed by deposition of thin-film ТiN of conductivity of n-type on single crystal supports of Si of conductivity of n-type by the method of reactive magnetron sputtering of pure titanium target in mixtures of argon and nitrogen at continuous voltage. The partial pressures of argon and nitrogen are 0.35 Pa and 0.7 Pa, respectively, at constant magnetron power 120 watts. The volt - ampere characteristics of the heterojunction TiN / Si were measured by the measuring complex SOLARTRON SI 1286, SI 1255. There is an analysis of temperature dependence of height of potential barrier and successive resistance of the heterojunction. The concentration of surface states (mismatch dislocations) N ss at the heterojunctions interface constitutes 2.67 × 10 13 sm -2 . It was determined that the dominant mechanism of current flow through the heterojunction n-TiN/n-Si at direct bias is well described in the tunnel model

High Temperature Stable Contacts for GaN HEMTs and LEDs

AbstractThere is continued interest in developing more stable contacts to a variety of GaN-based devices. In this paper we give two examples of devices that show improved thermal stability when boride, nitride or Ir diffusion barriers are employed in Ohmic contact stacks. AlGaN/GaN High Electron Mobility Transistors (HEMTs) were fabricated with Ti/Al/X /Ti/Au source/ drain Ohmic (where X is TiB2, ZrN, TiN, TaN or Ir) contacts and subjected to long-term annealing at 350°C. For GaN layers with an electron concentration of ∼3×1017 cm-3, the minimum specific contact resistance achieved is 6×10-5 Ω cm2 for Ti/Al/TiN/Ti/Au after annealing at 800°C. The specific contact resistance was found to strongly depend on the doping level, suggesting that tunneling is the dominant mechanism of current flow. By comparison with companion devices with conventional Ti/Al/Ni/Au Ohmic contacts, the HEMTs with boride-based Ohmic metal showed superior stability of both source-drain current and transconductance after 25 days aging at 350°C. The gate current for standard HEMTs increases during aging and the standard Ohmic contacts eventually fail by shorting to the gate contact. Similarly, InGaN/GaN multiple quantum well light-emitting diodes (MQW-LEDs) were fabricated with either Ni/Au/TiB2/Ti/Au or Ni/Au/Ir/Au p-Ohmic contacts. Both of these contacts showed superior long-term thermal stability compared to LEDs with conventional Ni/Au contacts.

Nitride-based Ohmic and Schottky Contacts to GaN

Ohmic and Schottky contact formation on n-GaN using ZrN, TiN and TaN-based metallization schemes was studied. For GaN layers with an electron concentration of ~3×1017 cm-3, the minimum specific contact resistance achieved is 6x10-5 Ω cm2 for Ti/Al/TiN/Ti/Au after annealing at 800{degree sign}C. The specific contact resistance was found to strongly depend on the doping level, suggesting that tunneling is the dominant mechanism of current flow. TiN/Pt/Au and ZrN/Pt/Au metallurgies exhibited rectifying behavior up to 900{degree sign}C anneal, the maximum barrier height being ~0.85 eV for ZrN/Pt/Au after 750{degree sign}C anneal. While this value is comparable to that of standard Ni/Au and Pt/Au rectifying contacts on the same n-GaN layer, the nitride-based metallization schemes show considerable smoother surface morphologies, even after annealing in the 750-900{degree sign}C range.

Electro-optical characterization and modeling of thin film CdS–CdTe heterojunction solar cells

Optoelectronic characteristics of thin film CdTe–CdS solar cells fabricated at four different laboratories were measured and analyzed. Current versus voltage measurements revealed that, under one sun illumination, tunneling was the dominant current flow mechanism in all cells. Tunneling was also the dominant current flow mechanism in the dark for all types except P3 which exhibited a generation-recombination type current flow process in the dark. A theoretical model involving bulk traps in CdTe and a charged thin layer (T-layer) near the junction under forward bias and/or illumination was developed. The model is able to explain all significant features in the experimental results obtained from current versus voltage, and capacitance.

Electrical properties of He+ ion-implanted GaInP

The electrical properties of high resistivity GaInP layers produced by He+ ion implantation have been studied. Thick high-resistivity layers (ρ > 107 Ω-cm) were obtained using multi-energy implants (80 keV, 120 keV, and 150 keV). Current-voltage (I-V) measurements of mesa diodes with two ohmic contacts indicate that in the temperature range from 200 to 300K, the dominant current flow mechanism in both n-type and p-type implanted materials is Poole-Frenkel emission, especially in the range of high electric field (>105 V/cm). The thermal activation energy Ea and the potential barrier height Φo of the generated deep levels are 0.16±0.005 eV and 0.33±0.005 eV, respectively. At low temperature, the hopping current dominates at low and moderate applied electric fields, and the I-V curves show an ohmic characteristic. The high-temperature annealing behavior of the implanted GaInP indicates that the compensation of free carriers in the material is dominated by damage-related levels, which are annealed out at high temperatures. In regard to typical alloying cycles of metal contacts in device fabrication, it is worth noting that the resistivity is still as high as 2 × 108 Ω-cm for n-type samples (5 × 107 Ω-cm for p-type) after 350°C annealing, which suggests that multi-energy He+ implantation is suitable for implant isolation in the GaInP device technology.

Increases in photovoltage of ‘‘indium tin oxide/silicon oxide/mat-textured n-silicon’’ junction solar cells by silicon preoxidation and annealing processes

Indium-tin-oxide (ITO)/silicon oxide/mat-textured n-Si junction solar cells having an energy conversion efficiency of 15% are fabricated by the spray pyrolysis method. Their characteristics and the junction properties are compared with the same junction solar cells having a flat Si surface. In cases where the ITO film is deposited on a hydrofluoric acid-etched mat-textured Si surface, the open circuit photovoltage (Voc) is low (405 mV). Scanning electron microscopy observation shows that high-density dislocations are formed near the Si surface, and the temperature dependence of the current-voltage characteristics suggests that the trap-assisted multistep tunneling through the Si depletion layer is a dominant current flow mechanism. In cases where the ITO film is deposited on a thermal silicon oxide-covered mat-textured Si surface, the formation of the dislocations is suppressed, and consequently Voc is increased to 485 mV. For this solar cell, a surface recombination current takes the dominant part of the dark current in the bias region below ∼250 mV, and a thermionic-assisted tunneling current is dominant in the higher bias region. For a cell where the thermal silicon oxide-covered mat-textured Si surface is annealed at 800 °C under nitrogen before the deposition of the ITO film, Voc is further increased to 540 mV, and the energy conversion efficiency of 15% is achieved. In this case, the thermionic-assisted tunneling current density is decreased by an increase in the barrier height due probably to a reduction in the density of the positive charge in the silicon oxide layer. The surface recombination current density is also reduced by the removal of interface states, leading to the improvement of the fill factor.

Triple implant (In,Ga)As/InP n-p-n heterojunction bipolar transistors for integrated circuit applications

For the first time (In,Ga)As/InP n-p-n heterojunction bipolar transistors (HJBT's) applicable to integrated circuits have been fabricated by triple ion implantation. The base has been formed by beryllium ion implantation and the collector by silicon ion implantation. The implants were made into an LPE-grown n-n (In,Ga)As/InP heterostructure on an n+-InP substrate. This inverted mode emitter-down heterojunction transistor structure demonstrates to a maximum current gain of 7 with no hysteresis in the characteristics. The ideality factors of the I B versus V BE , and I C versus V BE characterisitics with V CB = 0, are 1.25 and 1.08, respectively, indicating that the defect level in the herterojunction is low and that minority-carrier injection and diffusion is the dominant current flow mechanism.

New method for the determination of the surface barrier heights in MIS tunnel diodes (solar cells)

The methods commonly applied for the determination of the surface barrier heights of Schottky diodes are usually extended for the MIS tunnel structures characterization, although, in such cases both, their range of application and accuracy are often strongly reduced. In this paper a new photoelectric method for the determination of the surface barrier heights in MIS tunnel diode is proposed together with experimental results supporting its validity. The presence of the ultra-thin oxide layer between the metal and semiconductor does not reduce method's applicability as long as the direct semiconductor-metal tunneling is dominant current flow mechanism through the oxide layer. In the contrary to the previous methods it allow us to measure directly the barrier height for minority carriers, and therefore, is especially recommended for minority carrier dievices.

Current Flow through Thin Insulating Films: Basic Principles and Device Applications

The fundamental physics underlying current flow through thin insulating films is reviewed, with emphasis placed on those experiments central to the identification of the dominant current flow mechanism in a given structure. Recent data obtained on metal-insulator-metal structures incorporating single crystal thin films represents unambiguous observation of both thermionic emission and tunneling. Device applications of thin films are also summarized.

Electron tunneling and contact resistance of metal-silicon contact barriers

AbstractThe contact resistance of Al and Pt onn-type Si over a wide range of doping concentrations (1018 ș 2 × 1020cmȡ3) has been measured at both room temperature and liquid nitrogen temperature. These experimental results are compared with theoretical calculations based on a model with electron tunneling through the potential barrier at the interface as the dominant mechanism of current flow. Good agreement is found. It is hoped that this physical model can be used as a guideline in developing ohmic contacts for various semiconductor devices.

Tunneling in Semiconductors

Historical highlights of studies of current flow across metal-semiconductor contacts via electron tunneling are outlined. The physical origin of the space-charge potential at a rectifying metal contact on a degenerate semiconductor is illustrated with emphasis on the features of this potential which determine the dominant mechanism of current flow across the contact. Recent experiments on the tunneling characteristics of these junctions are described. Their interpretation in terms of phenomenological independent-electron models is discussed critically. The tunneling spectroscopy of collective excitations is described by use of the transfer-Hamiltonian model. The influence of features of the phonon spectra in the semiconductor on inelastic tunneling is illustrated for Ge. The effects of electronic interactions with collective excitations in the semiconductor electrode are discussed for phonons in Si and CdS, and for plasmons in GaAs. The references given herein supplement those presented in a recent comprehensive review.

PRESSURE SENSITIVITY OF GOLD-POTASSIUM TANTALATE SCHOTTKY BARRIER DIODES

The effect of localized uniaxial force (exerted by a hemispherical stylus) on the voltage-current relationship of Au-KTaO3 Schottky barrier diodes is described. Pronounced reversible changes were observed and characterized by stress-induced decreases of up to 0.8 eV in the metal-semiconductor barrier height. The observed diode n values [n ≡ (q/kT)(dV/d ln J)] at 300°K ranged from 1.05 to 1.10. This indicates that thermionic field emission may be the dominant current flow mechanism. An analysis of the pressure profile produced by the stylus yields 4 × 10−11 V-cm2/dyn for the pressure sensitivity of the barrier height.