Zinc Diffusion Research Articles

Diffusion of <sup>65</sup>Zn in AZ91 and QE22 Alloys with Saffil Reinforcement-Influence of Interfaces Matrix/Saffil

Diffusion of 65Zn in two commercial Mg-based alloys AZ91 and QE22 with short Saffil fibers was studied. Experiments were carried out in the temperature interval 648 – 728 K by serial sectioning method. The effective diffusion coefficients Deff were compared with 65Zn diffusion coefficients Dv obtained with the same alloys without Saffil fibers. The evaluation of the influence of the interface between the matrix and the fibers upon Deff was done and the zinc diffusion coefficient Di in the interface boundary matrix/Saffil was estimated. Unlike the Arrhenius-like behavior of volume diffusion in both alloys, it was observed that the temperature dependence of both Deff and Di was significantly concave in the measured temperature interval. This behavior was attributed to relaxation of thermo-elastic stresses in the composite induced by a large difference between coefficients of thermal expansion (CTE) of Saffil fibers and metal matrix. The maximum values of Deff and Di, respectively, lie close to 693 K, where CTE has a minimum.

Silver Self-Diffusion in Al<sub>2</sub>O<sub>3</sub>/QE22 Magnesium Alloy Matrix Composite

Self-diffusion of 110mAg has been investigated in fiber reinforced QE22 magnesium alloy matrix composite. Short Saffil fibers (97% -Al2O3 + 3% SiO2) were used as reinforcement. The diffusion measurements were carried out in the temperature interval 648 – 728 K by serial sectioning method. The volume diffusion coefficients Dv (alloy without reinforcement) and the effective diffusion coefficients Deff (alloy with reinforcement) were obtained by analysis of the penetration curves. The silver diffusion coefficient in the interface boundary matrix/Saffil Di was also estimated. The temperature dependence of volume diffusion coefficients Dv was compared with previous data measured using 65Zn in the same alloy and with literature data for Zn impurity diffusion in Mg single crystal. It was observed, that the temperature dependence of both Deff and Di was significantly non-linear in the measured temperature interval. This behavior supports previous observations with zinc diffusion in the same alloy.

Diffusion interaction between magnesium and zinc in 650nm laser diodes wafer

Abstract Zinc (Zn) diffusion in magnesium (Mg) doped AlGaInP based semiconductor laser diode epitaxial wafers has been investigated. After Zn diffusion, the hole concentration in the cladding was about one-fifth of previous value. In addition, Mg in AlInP layer was completely substituted by Zn and has moved towards the surface. Based on secondary ion mass spectrometric analysis, the interaction mechanism of Zn and Mg atoms was proposed.

Effect of Zincate Treatment on Adhesion of Electroless Ni-P Coating onto Various Aluminum Alloys

It is well known that the adhesion of the electroless Ni-P coating on aluminum alloy substrate can be remarkably improved by introducing the double zincate treatment as a pretreatment process. This study investigated the effects of the alloying element and zincate treatment on adhesion of electroless Ni-P coating on various aluminum alloy substrates using peeling test, FE-SEM and XPS. Surface morphology of zinc deposit from the 1st zincate treatment and its adhesive strength were changed, depending on the alloying element. The zinc deposit from the 2nd zincate treatment became uniformly thin, and the adhesive strength was improved irrespective of the alloying element. By dipping the zinc deposit obtained at the 1st zincate in 5% HNO3 solution, most of the zinc deposit on aluminum substrate was dissolved, but XPS analysis revealed that the existence of zinc, whose state was metal, at the surface of aluminum alloy substrate after this dipping. This zinc at the surface should be an important factor influencing morphology of zinc deposit at the 2nd zincate treatment, so that zinc deposit became highly uniform and thin. This zinc at the surface can be attributed to the diffusion of zinc and aluminum between the zinc deposit from the 1st zincate and the aluminum alloy substrate.

Capacitance–voltage measurements on p–n–p InP structures

Abstract The electrical properties of p-type layers of indium phosphide (InP) formed by the diffusion of zinc into n-type material were studied by capacitance–voltage measurements. A non-correspondence of atom and carrier concentrations was indicated, confirming previous four-point resistivity and Hall Effect studies. Using several specimens, a typical value of 25 was found from C −2 – V and C – V curves for the atom/carrier ratio. The dielectric constant of InP was taken to be 11. The width of the depletion region at an intermediate voltage (0.5 V) was typically 0.03 μm. It was concluded that further work on contacting procedures to produce a good Schottky Barrier at the contact–semiconductor interface should make this technique particularly useful for determining carrier profiles.

Hall Effect measurements on p-n-p InP structures

The electrical properties of p-type layers of indium phosphide (InP), formed by the diffusion of zinc into n-type material, are studied by Hall Effect measurements. A wide range of diffusion conditions are used and both homogeneously doped specimens and those containing a zinc atom concentration gradient are produced. A non-correspondence of atom and carrier concentrations is indicated, confirming previous four point resistivity studies. Carrier profiles are achieved by both serial sectioning and multiple specimen techniques. Contacting procedures are developed from which plots of carrier mobility versus carrier concentration, in the range 5 x 10(17) - 5 x 10(19) cm- 3, are produced for p-n-p InP. In the main, present results showed good reproducibility and conformed to the "rules" of the Van der Pauw technique.

Mechanism and kinetics of the formation of zinc pack coatings

A zinc deposition method that could be used instead hot-dip galvanizing is pack cementation, where the substrate is heated immersed in a powder mixture containing Zn and a halide activator (NH4Cl). In the present work the mechanism of this process is examined, along with the effect of temperature and heating time on the coating thickness and structure. For this purpose the coating was deposited and characterized with SEM, while the deposition mechanism was investigated with DSC. From the above examination it was deduced that the deposition of Zn takes place with a multiple-step mechanism, which involves several reactions in the gaseous phase including the formation of volatile zinc halides and finally the diffusion of zinc in the crystal lattice of the ferrous substrate. This procedure is accomplished at about 300°C and leads to the growth of a coating composed by two layers referring to Γ and δ phase of the Fe-Zn system. The coating deposition rate seems to be controlled by the zinc diffusion as its determination at 300 and 350°C showed, where it was deduced that the coating thickness is a linear function of the square root of heating time. However the coating structure is not affected by the heating time and temperature.

Effect of zincate treatment on adhesion of electroless Ni–P coating onto various aluminum alloys

It is well known that adhesion of electroless Ni–P coating onto aluminum alloy substrate can be remarkably improved by introducing the double zincate treatment as a pretreatment process. This study investigated the effects of alloying elements and zincate treatment on adhesion of electroless Ni–P coating onto various aluminum alloy substrates by using peeling test, FE-SEM and XPS. Surface morphology of zinc deposit from the 1st zincate treatment and its adhesive strength were changed, depending on the alloying element. The zinc deposit from the 2nd zincate treatment became thinly uniform, and the adhesive strength was improved irrespective of the alloying element. By dipping the zinc deposit obtained at the 1st zincate in 5% HNO3 solution, most of the zinc deposit on aluminum substrate was dissolved, but XPS analysis revealed that the existence of zinc, whose condition was metal, at the surface of aluminum alloy substrate after this dipping. This zinc at the surface should be an important factor influencing morphology of zinc deposit at the 2nd zincate treatment, so that zinc deposit became highly uniform and thin. This zinc at the surface can be attributed to the diffusion of zinc and aluminum between the zinc deposit from the 1st zincate and the aluminum alloy substrate.

Defect reactions in gallium antimonide studied by zinc and self-diffusion

Extrinsic diffusion of zinc (Zn) in gallium antimonide (GaSb) under Ga-rich conditions was analyzed on the basis of the kick-out and the dissociative diffusion mechanism. It is concluded that the changeover of interstitial Zn to substitutional gallium (Ga) sites is mainly mediated by Ga interstitials ( I Ga ). Fitting of the Zn profiles provides the relative contributions of I Ga to Ga diffusion. This contribution is lower than the directly measured Ga diffusion coefficient indicating that Ga diffusion in GaSb is rather mediated by Ga vacancies than by Ga interstitials even under Ga-rich conditions. This finding supports transformation reactions between native point defects that are confirmed by first-principles total-energy calculations. In addition Ga and Sb diffusion experiments under H 2 2 atmosphere were performed to reconcile the controversial data on self-diffusion in GaSb published by Weiler et al. and Bracht et al.

Four-point probe electrical measurements on p-n-p InP structures

The diffusion of zinc into n-type InP has been studied by four-point probe electrical measurements on homogeneously doped crystals at 750 ºC. The zinc carrier concentration in the diffused layer was approximately 3 x 10(18) cm-3 and its mobility was assumed to be about 40 cm² V-1 s-1. It was observed that the concentration of free carriers throughout the entire diffused region is always less than the number of introduced impurity atoms. Possible reasons are discussed to explain the observed differences. Moreover this non-correlation phenomenon did provide substantial backing to the Hall Effect and C-V measurements that are being carried out to further analyse the Zn-InP diffused layer.

Diffusion and reactivity of ZnO–MnO x system

The solid state interaction between ZnO and MnO x in air was investigated at different temperatures by means of the diffusion couple technique. No diffusion is observed at temperatures below 973 K. Above this temperature, Mn(IV) is already reduced to Mn(III) and the subsequent formation of Mn 2O 3 impels the diffusion of manganese into the ZnO pellet. However, it never enters the wurtzite lattice, so no homogeneous Mn:ZnO solid solution is formed. Simultaneously, Zn greatly diffuses in the manganese pellet, and as a consequence, a new phase layer develops at MnO x /reaction zone interface. A mixture of cubic and tetragonal spinel-type phases initially comprises this layer. However at higher temperatures, the tetragonal ZnMn 2O 4 spinel is the unique phase present in the interface, and it forms a physical barrier for further diffusion of both zinc and manganese species in the respective pellets of the couple. Differences arising between ZnO, MnO 2 and Mn 2O 3 crystal structures are behind these diffusion behaviors.

Zinc and gallium diffusion in gallium antimonide

Extrinsic diffusion of zinc (Zn) in gallium antimonide (GaSb) under Ga-rich conditions was analyzed on the basis of the kick-out and the dissociative diffusion mechanism. Accurate modeling of the experimental profiles by means of continuum theoretical calculations reveals that Zn diffusion proceeds via singly positively charged Zn interstitials $({\mathrm{Zn}}_{i}^{+})$. The changeover of ${\mathrm{Zn}}_{i}^{+}$ to substitutional gallium (Ga) sites, thereby forming the acceptor dopant ${\mathrm{Zn}}_{\mathrm{Ga}}^{\ensuremath{-}}$, is concluded to be mainly mediated by neutral ${I}_{\mathrm{Ga}}^{0}$ and singly positively charged Ga interstitials ${I}_{\mathrm{Ga}}^{+}$ via the kick-out mechanism. Fitting of the Zn profiles provides the reduced ${\mathrm{Zn}}_{i}^{+}$-mediated Zn diffusion coefficient and the relative contributions of ${I}_{\mathrm{Ga}}^{0}$ and ${I}_{\mathrm{Ga}}^{+}$ to Ga diffusion. These contributions to Ga diffusion are lower than the directly measured Ga diffusion coefficient, which indicates that Ga diffusion in GaSb is rather mediated by Ga vacancies than by Ga interstitials even under Ga-rich conditions. This finding supports the transformation reaction between native point defects in GaSb that was previously proposed to explain the Ga-vacancy-mediated diffusion of Ga in GaSb under Ga-rich conditions [H. Bracht et al. Nature (London) 408, 69 (2000)].

Epitaxial Design of a Direct Optically Controlled GaAs/AlGaAs-Based Heterostructure Lateral Superjunction Power Device for Fast Repetitive Switching

We outlined the epitaxial design methodology for a novel compound-semiconductor-based optically controlled power device for fast repetitive switching frequency. The proposed structure features gallium arsenide (GaAs/AlGaAs) lateral heterostructure with charge-balancing superjunction layers to make the breakdown voltage of the device independent of doping of the photo-absorbing GaAs active layer and linearly dependent on the lateral length. This structure also features parallel plate like p-n junction, which reduces local electric-field crowding and supports higher reverse bias during off-state. We show that the use of lattice-matched wider bandgap AlGaAs helps to achieve superjunction charge balancing without having any effect on switching performance of the device. We also show that the particular processing methodology (ion implantation over zinc diffusion) helps in improving the breakdown-voltage capability of the device

Zn diffusion behavior at the InGaAsP/InP heterointerface grown using MOCVD

Zinc (Zn) diffusion through MOCVD-fabricated InP and InGaAsP layers, and the corresponding Zn doping profile at the heterojunction interface were studied as part of the doping profile control for laser diodes. It was found that the Zn doping profile has specific discontinuity at the heterojunction in InGaAsP/InP heterostructures. Using secondary ionization mass spectrometer (SIMS) and Boltzmann–Matano analysis for different composition ratios ( x) of (1− x)InP– xInGaAs epitaxial layers grown on Zn-doped InP substrates, it was found that the Zn diffusion coefficients were proportional to the square of the concentration in the InP and InGaAsP layers. The Zn diffusion coefficient strongly depends on the component ratio ( x) for the (1− x)InP– xInGaAs layer. It was concluded that this diffusion property is based on the higher stability of the substitutional Zn content in the InGaAs layer compared to that in the InP layer. The dependence of the Zn diffusion coefficient on Zn concentration in the InGaAsP/InP layers is explained based on the main diffusion source being Zn at the interstitial sites. The thermal equilibrium between Zn-interstitial and Zn-substitutional (interstitial–substitutional model) describes these Zn diffusion properties. Marked Zn concentrations at InGaAsP/InP heterojunctions are referred to as “pileups”, and are affirmed due to the difference in physical properties between InP and InGaAs. With different composition ratios ( x) of InP/InGaAsP layer growth, pre-control of the Zn concentration and strict limitations on the growth conditions before diffusion are indispensable for lasers requiring a precisely controlled doping concentration.

Direct Kinetic Correlation of Carriers and Ferromagnetism inCo2+: ZnO

The hypothesis that high-Curie-temperature ferromagnetism in cobalt-doped ZnO (Co2+: ZnO) is mediated by charge carriers was tested by controlled introduction and removal of the shallow donor interstitial zinc. Using oriented epitaxial Co2+: ZnO films grown by chemical vapor deposition, kinetics measurements demonstrate a direct correlation between the oxidative quenching of ferromagnetism and the diffusion and oxidation of interstitial zinc. These results demonstrate controlled systematic variation of a key parameter involved in the ferromagnetism of Co2+: ZnO and, in the process, unambiguously reveal this ferromagnetism to be dependent upon charge carriers. The distinction between defect-bound and free carriers in Co2+: ZnO is discussed.

Photovoltaic Cells Based on GaSb and Ge for Solar and Thermophotovoltaic Applications

In the present work, high efficient photovoltaic (PV) cells based on gallium antimonide have been developed and fabricated with the use of the liquid phase epitaxy (LPE) and diffusion from the gas phase techniques. They are intended for conversion of the infrared (IR) part of the solar spectrum into electricity by tandems of mechanically stacked cells and for conversion of the thermal radiation of emitters heated by the sunlight. On the ground of investigation of the LPE temperature regimes and the tellurium doping effect, GaSb PV cells have been fabricated with the efficiency of 6% at the concentration of 300 suns behind the single-junction GaAs top cell and of 5.6% at the same sunlight concentration of the cells behind the dual-junction GaInP∕GaAs structure, the substrate thickness being 100μm (the efficiency of PV cells was calculated for AM1.5D Low AOD spectrum, 1000W∕m2). The rated efficiency of conversion of solar powered tungsten emitter radiation by PV cells based on gallium antimonide in a thermophotovoltaic (TPV) module appeared to be about 19%. Photovoltaic cells based on germanium with a wide-gap GaAs window grown by LPE or metalorganic chemical vapor deposition and with a p-n junction formed by means of the zinc diffusion from the gas phase have been fabricated. Ge based PV cells without a wide-gap GaAs window had the efficiency of up to 8.6% at a concentration of 150 suns. The efficiency of Ge based cells with a wide-gap GaAs window was 10.9% at the concentration of 150 suns. 4.3% efficiency Ge cells behind a single-junction GaAs top cell at the concentration of 400 suns have been also obtained. The maximum rated conversion efficiency of Ge PV cells appeared to be about 12% in the case of conversion of the tungsten emitter thermal radiation. These efficiency values for Ge based cells are among the highest.

Relations between the parameters of grain-boundary diffusion of zinc in aluminum

Experimental results on the grain-boundary diffusion of zinc in aluminum bicrystals containing 〈100〉 and 〈111〉 tilt boundaries at normal and high hydrostatic pressures have been considered. A comparison of the diffusion activation energies and the activation volumes for grain boundaries having the same crystallographic parameters has revealed a linear relation between these kinetic constants. The diffusion activation energy is found to increase with the activation volume. This relation is shown to correspond to the compensation effect well-known in diffusion theory.

InAs pixel matrix detectors fabricated by diffusion of Zn in a metal-organic vapour-phase epitaxy reactor

We introduce a zinc diffusion process to fabricate an InAs-based detector matrix using an atmospheric pressure metal-organic vapourphase epitaxy reactor. Current–voltage characteristics are measured and different diffusion parameters are experimented. Spectral alpha radiation response of the diode is reported. To our knowledge, this is the first time that InAs was used as an alpha particle detector.

Improvement of hot-dip zinc coating by enriching the inner layers with iron oxide

The performance of hot-dip galvanic coating formed on steel not only depends on the alloy composition of the superficial layer but also significantly, on the composition of the inner alloy layers at the coating/substrate interface. Further, the presence of barrier oxide layers, if any can also improve the performance of galvanic coating. In the present work, the effect of inner iron oxide barrier layer formed prior to hot-dip galvanization was investigated. A continuous and adherent iron oxide layer was formed on steel by anodic oxidation of the steel substrate. Although the wettability of oxide surface by liquid zinc was initially poor, the increase in dipping time and the transition of the oxide layer to unstable form due to the presence of Cl − ion in the flux facilitated localized growth of Fe–Zn alloy phases. The inhibitive nature of the oxide layer was temporary, since the presence of Cl − induces micro cracks on the oxide surface thereby facilitating better zinc diffusion. The modification of the substrate structure during galvanization was found to influence the galvanizing process significantly. The present study predicts scope for application of this process for protection of rusted steel specimens too.

Zinc Self-Diffusion in ZnO

This work deals with the study of zinc self-diffusion in ZnO polycrystal of high density and of high purity. The diffusion experiments were performed using the 65Zn radioactive isotope as zinc tracer. A thin film of the tracer was deposited on the polished surface of the samples, and then the diffusion annealings were performed from 1006 to 1377oC, in oxygen atmosphere. After the diffusion treatment, the 65Zn diffusion profiles were established by means of the Residual Activity Method. From the zinc diffusion profiles were deduced the volume diffusion coefficient and the product dDgb for the grain-boundary diffusion, where d is the grain-boundary width and Dgb is the grain-boundary diffusion coefficient. The results obtained for the volume diffusion coefficient show good agreement with the most recent results obtained in ZnO single crystals using stable tracer and depth profiling by secondary ion mass spectrometry, while for the grain-boundary diffusion there is no data published by other authors for comparison with our results. The zinc grain-boundary diffusion coefficients are ca. 4 orders of magnitude greater than the volume diffusion coefficients, in the same experimental conditions, which means that grain-boundary is a fast path for zinc diffusion in polycrystalline ZnO.