Mechanism Of Current Flow Research Articles

Surface current and hysteresis in fine filament NbTi superconductors

Measurements of the hysteresis loops, the magnetic moments obtained by cooling in a constant field, and the critical current density of submicron NbTi filaments are consistent with the assumption that surface current is the principal mechanism of current flow in these filaments.

Experimental determination of the mechanism of transient single-injection current flow in dielectrics

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Optical and electrical characterizations of laser–chemical-vapor-deposited aluminum oxynitride films

Composition-dependent optical and electrical properties of (Al2O3)1−c-(AlN)c composite films (0≤c≤1) are investigated herein. The films are deposited by the laser-assisted, chemical-vapor-deposition (L-CVD) technique. Film composition is controlled by background vacuum level (e.g., O2) and substrate temperature. Optical parameters of the oxynitride films on quartz substrates are evaluated from spectrophotometric transmittance characteristics. Infrared absorption spectra are used to identify chemical composition of the films. Electrical-field-dependent current flow mechanisms are investigated for Al-insulator-n-Si metal-insulator-semiconductor (MIS) structures. Current-voltage (I-V) characteristics of the MIS structures exhibit two alternative states: the original and the programmed states. The original state I-V characteristics are obtained for virgin films by first application of the tracing voltage. Current density versus electric field follows both exp E and exp (E)1/2 regions. The MIS structure makes a transition from the original to a programmed state at high electric field due to the establishment of a persistent polarization field. Programmed MIS structures exhibit two alternative I-V characteristics corresponding to whether the applied and the polarization field are in the same or opposite directions. Capacitance-voltage (C-V) characteristics of L-CVD (Al2O3)1−c-(AlN)c devices exhibit composition-dependent hysteresis. A large clockwise hysteresis is observed for AlN while smaller size anticlockwise hysteresis is obtained for the Al2O3 case.

Transient Currents in Dielectrics at Non-Linear Law of Single Injection

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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.

Effects of electron detachment from negative ions on the current-flow mechanism in a medium-pressure glow discharge

Effects of electron detachment from negative ions on the current-flow mechanism in a medium-pressure glow discharge

Electrical properties of InP MIS devices

Thin film metal-insulator-semiconductor devices have been prepared on n-type InP substrates. The metal used was aluminium and the insulating oxide film was produced using an anodisation technique. Diodes were made with oxide thicknesses of 40 AA and 110 AA and were evaluated using current-voltage measurements over the temperature range 150-350K and also capacitance-voltage techniques. Both sets of measurements were compared with current metal-insulator-semiconductor theory and values were obtained for the barrier height in the semiconductor. Reasonable agreement was found but an anomaly previously observed in the Richardson plot in Al-InP Schottky barriers was again evident in the devices. The capacitance-voltage results indicated a surface-state density in the region of 1012 cm-2 eV-1. Values were also obtained for the barrier height presented to electrons by the insulating layer. This proved to be rather smaller than expected, which suggests that the mechanism of current flow through the layer is not simple tunnelling.

Properties of the contact on ion cleaned n and p type silicon surfaces

Schottky contacts were produced by silver evaporation on Si(100) surfaces cleaned by ion sputtering and partial annealing. The samples work function were measured before and after metal deposition with the Kelvin method, in an experimental set-up which allowed a topografical study and direct comparison between n and p types. Clean surfaces with and without a residual layer of oxide was achieved and controlled by AES. It was found that the Fermi level of all the surfaces was pinned by donor states created by the bombardment and that there was no barrier on n type and an important surface barrier on p type. The diodes we obtained presented no barrier on n type and a rectifying contact on p type. So we deduced that the Schottky barrier is already fully formed before metal contact is achieved. Furthermore study of the electrical properties of the diodes had shown that the bombardment creates donor states responsible for the barrier and a perturbated layer with deep acceptor traps responsible for the current flow mechanism. A residual layer of oxide and a post annealing of the device did not noticeably change the Schottky barrier in the diodes achieved on p type but led to clearly differenciated performances for the diodes achieved on both p and n type substrate. So we therefore concluded that the characteristics of the deep acceptor traps of the superfacial layer are modified by the oxide and annealing, both of which on the other hand having no effect on the surface donor states.

Metallurgically grown Schottky junction in directionally solidified eutectic Ag–Si alloys

AbstractMetallurgically grown M(metal)–S(semiconductor) phase boundaries in directionally solidified AgSi alloys were investigated relative to their behaviour as Schottky junctions. By the aid of point contacts I/V characteristics have been measured which correspond to these ones of Schottky diodes. The Si crystallites were proved to be n‐doped. Reverse breakdown voltages of 8 … 24 V are not incompatible with the purity of the used materials. In forward direction the value of diode factor n = 1.1 … 5 shows the existence of several current flow mechanisms. In order to be able to interpret the characteristics it is necessary to have exact information on the specific resistivity of the Si crystallites and on the content of grain boundaries and dislocations in silicon. Beyond that the complicated shape of Si crystallites prevents the necessary determination of the interface size.

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.

Glow discharge in a gas flow

The status of research on glow discharges in a gas flow, used in pumping fast-flow lasers, is reviewed. Systematic study of this discharge began about 10 years ago. This discharge form, according to a number of properties (current flow mechanism, nature of the development of instabilities, etc.), differs considerably from the well-studied glow discharge in tubes. One of the distinguishing features of such a discharge is the negligibly small role of ionization in a large part of the positive column, so that narrow regions near the electrodes contribute most of the positive ions and electrons. Negative ions, which compensate the charge of the positive column, are generated in its volume. The discharge turns out to be weakly inhomogeneous in the direction from the cathode to the anode and the ion currents can form an appreciable part of the total current. These facts have not yet been sufficiently widely discussed in reviews and monographs. In this review, results of experimental investigations of the mechanism of current flow, energy balance, plasmochemical processes, and discharge instabilities are presented, the mathematical models used in their analysis are analyzed, and the possibilities for increasing the stability and efficiency of the discharge in fast-flow lasers are examined.

Magnetic-field-dependent zero-bias anomaly in Al-oxide-Ga (granular) thin-film tunnel junctions

High-T/sub c/ gallium films were prepared by evaporating gallium in partial pressure of oxygen and electron tunneling characteristics of tunnel junctions of the form Al-oxide-Ga were studied with gallium film being in the superconducting and in the normal states. In the superconducting state a sharp, single gap was observed, and from these characteristics it was ascertained that the mechanism of current flow was indeed through electron tunneling. In the normal state a magnetic-field-dependent zero-bias anomaly corresponding to a resistance maximum at zero bias was observed. The conductance varied as V/sup 1/2/ for all the magnetic field values. The bias dependence is in agreement with recent theories on metal-insulator transition in amorphous materials; however, the magnetic field dependence is a novel feature.

The Al-(n-InP) Schottky barrier

Schottky barriers have been prepared by the evaporation of aluminium on to bulk-grown n-type InP slices. Reproducible devices were obtained providing sufficient care was taken over the preparation of the semiconductor surface. Current-voltage, capacitance-voltage and photocurrent measurements were made on the diodes. The current measurements showed the ideality factor n, to be close to unity at room temperature and above, indicating that the main mechanism of current flow was thermionic emission. Below room temperature, the ideality factor increased. The capacitance measurements indicated the presence of a deep donor about 1 eV below the conduction band edge. All three measurement techniques gave a calculated value of Schottky barrier height in the region of 0.5 eV. The variation of barrier height with temperature was found to be 4*10-4 eV K-1, which corresponds closely with the temperature variation of the band-gap of InP.

Grain boundary effects and conduction mechanism studies in chromium metal-insulator-silicon solar cells on polycrystalline silicon

Chromium metal-insulator-silicon (MIS) solar cells fabricated on Wacker polycrystalline silicon and electron-beam-deposited thin film silicon were studied to determine current flow mechanisms. Wacker polycrystalline p-type silicon was shown to produce MIS solar cells which exhibit surface-state-controlled current for T>150 K and tunneling-controlled current at lower temperatures. MIS cells on unpolished Wacker silicon are clearly space charge limited. Electron-beam-deposited polycrystalline silicon 20 – 30 μm thick has a conductivity which may be limited by the grain boundary trap density or the availability of free carriers. Surface state analysis, laser scan data and diffusion length studies also show the limitations which exist at grain boundaries of polycrystalline silicon.

Spray-deposited ITO—Silicon SIS heterojunction solar cells

A systematic study of semiconductor-insulator-semiconductor (SIS) solar cells has been undertaken on n-type silicon using spray-deposited indium-tin-oxide (ITO) for the window layer of the heterostructure. The optical and electrical characteristics of the ITO layer as well as the thickness of the I layer have been optimized to yield the following photovoltaic parameters on 0.5-Ω . cm n-Si: V_{OC} = 0.52 V, J_{SC} = 31.5 mA/cm2(adjusted for Ag grid area), FF= 0.70 , and illuminated area η = 11.5 percent. The dark I-V and C-V characteristics have also been evaluated to identify the mechanisms of barrier formation and current flow.

Si and GaAs SIS Heterostructure Solar Cells Using Spray-Deposited ITO

A systematic study of semiconductor-insulator-semiconductor (SIS) solar cells has been undertaken on n-type Si and GaAs using spray-deposited indium-tin oxide (ITO) for the window layer of the heterostructure. The optical and electrical characteristics of the ITO layer as well as the thickness of the I-layer have been optimized to yield the following photovoltaic parameters on 1 Ω-cm n-Si: Voc=0.52 V, Jsc=31.5 mA/cm2 (adjusted for Ag grid area), FF=0.70 and effective area η=11.5%. The dark I-V and C-V characteristics have also been evaluated to identify the mechanisms of barrier formation and current flow.

Surface-barrier structures on AlxGa1?xSb. I. Preparation and physical model of the contact

The optimal conditions for preparing the surface and electrochemically depositing the metal have been determined for surface-barrier junctions of palladium on n-type gallium aluminum antimonide. The temperature and composition dependences of the voltage-current and voltage-capacitance characteristics of the junctions have been measured. When combined with the frequency dependence of the capacitance, these data show that, depending on the condition during formation, nearly ideal Schottky barriers are formed (i.e., a metal-intermediate layer-semiconductor system). The mechanism for current flow depends on the structure of the contact and the solid-solution composition. Anomalous barrier behavior at low temperatures is due to specific properties of the solid solution.

Radiation Effects in GaAs MIS Schotiky Diodes

The electrical characteristics of GaAs MIS Schottky barrier diodes using a thin (~60 Å) native oxide layer were evaluated before and after ionizing γ-ray irradiation and fast-neutron irradiation. No change in electrical behavior could be observed with a Cobalt-60γ - irradiation level as high as 1.5 × 107 rads (Si) absorbed dose. The MIS diodes together with reference MS diodes were progressively irradiated with neutrons from a fluence of 5 × 1013 n/cm2 to 8 × 1014 n/cm2. Carrier compensation in GaAs is negligible at these radiation levels, but significant changes were observed in I-V characteristics. The low-voltage forward I-V exhibited an appreciable increase in depletion region recombination current resulting from a decrease in carrier lifetime, while the diode ideality factor was found to increase at higher forward voltages. The reverse current showed orders of magnitude increase with irradiation, and its strong field dependence and relatively weak temperature dependence suggests field emission through traps as possible mechanism of current flow. The attenuation in reverse current caused by the oxide layer is seen to be reduced after neutron irradiation. Finally, the increase in reverse current is found to vary approximately in proportion to the neutron fluence. The implications of radiation results on practical devices are briefly discussed.

Zero-bias anomaly in GaAs/Mo tunnel junctions

A large zero-bias anomaly has been observed in the point contact tunnel junctions made between a degenerate p-type GaAs and Mo. The anomaly corresponds to a resistance peak centered at zero bias. The junction resistance at zero bias is a strong function of temperature, increasing with decreasing temperature. A quantitative study of the voltage and temperature dependence of the zero-bias anomaly has been made. No effect of the magnetic field up to 12 kG was found. When the temperature was lowered below the transition temperature of Mo, the superconducting energy gap of Mo was observed, which indicated that the mechanism of current flow is by electron tunneling.

Changes in conductivity of metal-dielectric-metal and metal-dielectric-semiconductor structures under the action of radiation

This study is an experimental investigation of the effects of radiation on conductivity of metal-dielectric-metal (MDM) and metal-dielectric-semiconductor (MDS) structures. A brief theoretical analysis of current flow mechanisms in the dielectric layer of an MDS structure is given. A physical interpretation of the experimental results obtained is offered. It is shown that the change in conductivity of MDM and MDS structures upon irradiation is dependent on the type of dielectric film used and the type of radiation.