Electromigration Of Hydrogen Research Articles

Impact of Electrical Stress on $\gamma$ Ray Irradiated Double Polysilicon Self-Aligned (DPSA) PNP Bipolar Transistors

Anomalous irradiation response to total ionizing dose effects of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co γ ray in double polysilicon selfaligned (DPSA) bipolar PNP transistors at a low dose rate was observed. It is experimentally revealed that the anomalous current gain (β) enhancement in Emitter-Base (E-B) forward-biased transistors during irradiation originates from a base current decrease. Based on the comparative forward high-current stress and forward-biased irradiation experimental results, the anomalous phenomenon can be ascribed to the atomic hydrogen electromigration and subsequent passivation of electronic interface traps located at the polysilicon grain boundaries and poly/monosilicon interfaces of DPSA's poly emitter contact layers. Although current gain enhancement occurs both in high-current stress and forward-biased irradiation stress PNP transistors, the physical mechanisms responsible for the variations are quite different. In the case of forward high-current stress, the damage mainly affects excessive base current of non-ideal components and decreases the emitter resistance. For forward-biased ionizing radiation stress, the damage not only induces both ideal and non-ideal components of the base current increase in the low bias region but also increases emitter resistance.

Nonuniformity of carrier injection and the degradation of blue LEDs

The distribution of electroluminescence (EL) intensity over the area and in the course of time before and after the optical degradation of blue InGaN/GaN LEDs is studied. Current-voltage characteristics have been recorded. It is found that the initially bright luminescence near the region of metallization of the p-contact turns weak after the degradation of an LED. The time delay of ∼20–40 ns is observed in the distribution of EL intensity over the area of LEDs after their degradation. We suppose that a rise in the excess current after degradation is due to the density increasing of the InGaN/GaN interface states and the formation of an electrical dipole, which lowers the potential barriers in p-GaN and n-GaN layers. The corresponding increase of capacitance leads to a time delay in the spreading of the injection current and in the distribution of the emission brightness over the area. The lateral nonuniformity of the carrier injection into the quantum, well before and after optical degradation, is attributed to diffusion and electromigration of hydrogen, induced by mechanical stress. The metallization of the p-contact may be the source of mechanical stress.

Influence of external stretching on hydrogen electromigration in Pd and PdCu, PdAg alloys

Influence of external stretching of Pd and Pd 77Cu 23 and Pd 77Ag 23 alloys on hydrogen electromigration in these systems was investigated. The electro-resistivity method was applied in the investigations. It was found that in order to furnish a full description of the kinetics and dynamics transport of hydrogen in the externally applied electric field to samples in the state of elastic and plastic stretching, it is not sufficient to provide a functional dependence of two commonly used parameters (diffusion coefficient D and effective valence Z eff) on degree of deformation. To describe the electromigration in these conditions a mathematical model was applied, which assumes the existence of two diffusion mechanisms: interstitial and defect-interstitial ones, each of which is characterized by the above-mentioned parameters. For each of the mechanisms, the dependence of these values on external stretching was determined.

Electromigration and Diffusion of Hydrogen in Palladium Defected by Cold Rolling

Influence of defects induced by cold rolling on hydrogen electromigration in palladium was investigated. It was found that the obtained results can not be explained by means of the occurrence of only one (interstitial) diffusion mechanism. However, accepting the assumption that in the process of hydrogen electromigration in defected palladium there appear two mechanisms of diffusion, that is interstitial (i) and interstitial-defective (i-d), that describe the experimentally obtained dependences well enough. In order to determine the influence of kinds of defects and their concentration on hydrogen electromigration, examination of changes in positron lifetimes and electric resistance in dependence on the degree of cold working on palladium were additionally conducted.

A hydrogen traffic jam in YH x

Electromigration of hydrogen in the YH x switchable mirror system is studied with a simple optical technique. The YH 3− δ –YH 2+ ε phase boundary moves towards the anode with a velocity v pb , that becomes constant for large t. A spectacular effect takes place when the phase boundary reaches an artificial discontinuity in the electric field: a ‘hydrogen traffic jam’ is formed. This phenomenon is succesfully simulated using the exact solutions of a non-linear electromigration equation and a large wind force coefficient K=−23 mΩcm. It is in principle possible to reach very high chemical potentials, comparable to those in high pressure experiments, in the traffic jam area.

Influence of the external stretching on hydrogen electromigration in palladium

Electromigration and diffusion of hydrogen in palladium depending on unit elongation were investigated. It was found that the obtained experimental results cannot be described by means of a single flux of hydrogen, which diffuses in a gradient of electric field. In order to effectively explain the obtained results, a theoretical model was elaborated. It assumed the existence of the following two fluxes of hydrogen in the stretched metal: • J i—of migration, according to the interstitial mechanism, and • J i-d—of migration, according to the interstitial-defective mechanism. Dependence of effective valences and diffusion coefficients for both mechanisms of transportation were determined in relation to the degree of deformation.

Influence of crystal defects on the electromigration of the hydrogen in palladium

Electromigration and diffusion of hydrogen in palladium defected through quenching to liquid nitrogen temperature were investigated. It was found that the obtained experimental results cannot be described by means of a single flux of hydrogen which diffuses in a gradient of electric field. In order to effectively explain the obtained results, a theoretical model was elaborated. It assumed the existence of the following two fluxes of hydrogen in the quenched metal: • J i—of migration, according to the interstitial mechanism, and • J i–d—of migration, according to the interstitial-defective mechanism. Dependence of effective valences and diffusion coefficients for both mechanisms of transportation was determined in relation to the initial temperature of the quenching.

Correlated electromigration of H in the switchable mirror YH(3-delta)

Electromigration of hydrogen in YH(3-delta) is studied by exploiting the H concentration dependence of the optical transmission of YH(3-delta). We find the effective valence Z* of H in YH(3-delta) to be negative. Its value is dominated by a huge wind-force-like term, i.e., Z* approximately K/rho, with K approximately -60 mOmega cm. This value is 3 orders of magnitude larger than typical for H in metals. In an Arrhenius plot, the ratio of hydrogen and electron fluxes extrapolates to unity at infinite temperature, suggesting a one-to-one correlation of hydrogen and electron hopping. We discuss our results in the light of strong electron correlation theories which predict each proton to bind two electrons in a sort of Zhang-Rice singlet.

Investigation of diffusion and electromigration of hydrogen in palladium and PdAg alloy

Diffusion and electromigration of hydrogen in PdH 0.1, Pd 77Ag 23H 0.1 and Pd 50Ag 50H 0.1 alloy were measured by means of resistivity method. It is known that hydrogen migrates towards the cathode within the temperature range of 300–473 K in the PdH 0.1 and Pd 77Ag 23H 0.1 system. In Pd 50Ag 50H 0.1, hydrogen migrates towards the cathode below 400 K, but towards the anode at higher temperatures. Its effective valency increases together with temperature. At the same time it satisfies the linear dependence on inverse specific resistance ρ: Z eff= Z i+( k/ ρ). The constants Z i and k have the following values: (1.05±0.01) and −(3.81±0.04)×10 −8 Ω m for hydrogen in PdH 0.1, (0.73±0.01) and −(11,82±0.03)×10 −8 Ω m for hydrogen in Pd 77Ag 23H 0.1, and (0.79±0.04) and −(29.4±1.4)×10 −8 Ω m for hydrogen in Pd 50Ag 50H 0.1, respectively. The activation energies of hydrogen diffusion amount to (0.23±0.001) eV/at. for PdH 0.1, (0.221±0.006) eV/at. for Pd 77Ag 23H 0.1 and (0.31±0.02) eV/at. for Pd 50Ag 50H 0.1 alloys, respectively.

Visualization of hydrogen migration in solids using switchable mirrors

Switchable mirrors1,2,3 made of thin films of the hydrides of yttrium (YHx), lanthanum (LaHx) or rare-earth metals exhibit spectacular changes in their optical properties as x is varied from 0 to 3. For example, α-YHx 2.85 is a yellowish transparent semiconductor. Here we show that this concentration dependence of the optical properties, coupled with the high mobility of hydrogen in metals, offers the possibility of real-time visual observation of hydrogen migration in solids. We explore changes in the optical properties of yttrium films in which hydrogen diffuses laterally owing to a large concentration gradient. The optical transmission profiles along the length of the film vary in such a way as to show that the formation of the various hydride phases is diffusion-controlled. We can also induce electromigration of hydrogen, which diffuses towards the anode when a current flows through the film. Consequently, hydrogen in insulating YH3−δ behaves as a negative ion, in agreement with recent strong-electron-correlation theories4,5. This ability to manipulate the hydrogen distribution (and thus the optical properties) electrically might be useful for practical applications of these switchable mirrors.

Isotope effect of diffusion and electromigration of hydrogen in nickel

Isotope effect of diffusion and electromigration of hydrogen in nickel

An ERD based study of the electromigration of hydrogen in V, Ta, Nb, and Ti

Elastic recoil detection (ERD) has been successfully applied to the measurement of hydrogen and deuterium electromigration in metals. Besides providing a sensitive and direct measure of hydrogen isotope concentrations in the direction of transport, advantages over other techniques include excellent spatial resolution and the ability to distinguish between surface and bulk effects. Using incident 4He ions to determine the lateral redistribution of hydrogen due to the presence of a large electric current, we have measured the effective charge Z ∗ of H in α-Nb, Ta, and Ti under various conditions. We also demonstrate the simultaneous determination of Z ∗ of H and D in α-V. Data analysis methods and sample preparation are discussed.

Observation of electromigration of hydrogen in polycrystalline silicon using poly emitter bipolar transistors

Electromigration of hydrogen inside polycrystalline silicon (polysilicon) has been observed for the first time. Experiments were conducted on polysilicon emitter (poly emitter) n-p-n transistors with and without atomic hydrogen inside polysilicon. The current gain (β) of n-p-n was selected to monitor electromigration of hydrogen during current stress because of its high sensitivity to hydrogen passivation of dangling bonds. The major characteristics of hydrogen electromigration are shown in this letter.

Electromigration of hydrogen in B, Nb and Ta: a new description of the measured sample-resistivity-dependent effective valence

Resistivity-dependent expressions for the direct force valency Zd are presented, starting from a recently proposed new theory for the driving force in electromigration. Using these expressions a good description is found for the measured effective valency of hydrogen in the transition metals V, Nb and Ta. Fits based on a constant Zd which are at present available led to the values 1.1, 0.44 and 1.23 for Zd in the three hosts in question. These values are not understood yet. According to the new expressions, Zd ranges between the bare-charge value of unity and the completely screened value of zero, which are limiting values obtained in the high- and low-resistivity limits, respectively. While the available experimental data are not able to discriminate between the description with a constant Zd and the new one with a resistivity-dependent Zd, the latter can be considered as much more satisfactory. Regarding a long-standing controversy concerning the magnitude of the direct valency, it is concluded that the new theory in fact reconciles the two extremes involved.

Relaxation-time dependence of the driving force in electromigration

The relaxation-time dependence of the driving force in electromigration is calculated from an expression derived by Schaich using a density-matrix analysis in the relaxation-time approximation. The result does not support Lodder's conjecture on the dependence of the force on the relaxation time. It is shown that Lodder's conjecture is based upon a subtle error which he made in evaluating a response function in the limit of large relaxation time. Recent experimental results for hydrogen electromigration in disordered transition-metal alloys are discussed in the light of existing theory, and it is concluded that additional effects need to be incorporated into the theory in order to explain these experiments.

Exact linear-response result for the driving force in electromigration

Using linear response theory the driving force on an impurity of arbitrary scattering strength in jellium is shown to reduce exactly to the classical wind force. Implications for the direct force on a substitutional impurity and for low conductivity samples are discussed. Our results, which are consistent with recent measurements of the electromigration of hydrogen in concentrated Nb-V alloys, can be considered as conclusive in the long-standing controversy concerning the magnitude of the direct force.

Electromigration of hydrogen in alloys: Evidence of unscreened proton behavior.

Electromigration of hydrogen in alloys: Evidence of unscreened proton behavior.

Electromigration of hydrogen in vanadium and its alloys

Electromigration and diffusion of hydrogen have been investigated for vanadium and vanadium alloys containing Ti, Cr, Fe or Mo. Both the effective charge number Z ∗ and the diffusion coefficient D decrease by the addition of Ti and Cr, but are not much affected by Fe and Mo. A model of hydrogen trapping by substitutional elements, previously introduced to account for a decrease in D by solute addition, cannot explain a decrease in Z ∗ in a straightforward manner. The change in the electronic structure due to alloying seems to be responsible for the decrease in Z ∗ .

Electromigration of hydrogen in vanadium, niobium and tantalum

The electromigration of hydrogen in VHx, NbHx and TaHx (with x approximately=0.01) has been studied between 275 and 525K using a new experimental technique. In this method the evolution of the hydrogen concentration profile during the migration process is detected by measuring capacitatively the local dilatation of the sample. From the temperature dependence of the effective valence Z* of hydrogen is is concluded that the valence associated with the direct force in electromigration is essentially different from the bare valence of a proton for Nb and Ta, whereas for V a value close to +1 is found. The 'wind-force' contribution to Z* is for all metals under consideration of the same order of magnitude as the direct force. In V and Nb the wind force has the same sign as the direct force, whereas an opposite sign is found in Ta. The results are discussed within the framework of existing theories of electromigration.

Multidilatometric methods for measurements of the diffusion and electromigration of hydrogen in metals

A new technique for studying the diffusion and electromigration of hydrogen in metals is presented. In this technique the evolution of the hydrogen concentration profile during the diffusion process is detected by local dilatation measurements (at several positions along the diffusion direction) on the sample by means of a capacitance technique. This multidilatometric method is applied to the study of the diffusion of hydrogen in palladium and the electromigration of hydrogen in vanadium, niobium and tantalum. Representative experimental results are in good agreement with those obtained by using other methods.