Gallium Impurity Research Articles

Implanted gallium impurity detection in silicon by impedance spectroscopy

The results of determining the energy levels of boron-doped silicon implanted with gallium ions by impedance spectroscopy are reported. In the as-implanted sample the boron level remains the same and a second level appears close to the Ga-level reported in literature. In the sample annealed at 1000 °C, two levels are observed neither of which corresponds to the literature values for boron and gallium. It is assumed that in the as-implanted sample this method detects levels of gallium atoms located at a depth where ions penetrate due to the channeling effect, since a large concentration of defects at shallower depths does not allow detection of energy levels due to the Fermi level pinning. Explaining the results for the sample annealed after implantation requires additional research. The main result of this work is to establish the possibility of detecting impurity levels in ion-implanted silicon by impedance spectroscopy even in the absence of subsequent annealing.

Radioactivity yields of Galium-67 applicable for scintigraphy of various visease in nuclear medicine

In nuclear medicine, gallium-67 (67Ga) is potentially applied for imaging a certain type of tissue. In this investigation, 67Ga is theoretically studied in terms of its potential radioactivity yield at the end of various energetic proton bombardments. Nuclear cross-sections derived from the TALYS-2017 codes were used to perform yield calculations of 67Zn(p,n)67Ga and 68Zn(p,2n)67Ga nuclear reactions. Two different targets –enriched 67Zn and 68Zn targets – were simulated in the calculations. The calculated yields suggested that a maximum of 27.37 MBq/μAh when enriched 67Zn target is irradiated with 15-MeV protons, whereas 46.99 MBq/μAh could be generated following a 30-MeV proton bombardment of enriched 68Zn target. Various radioactive gallium impurities such as 63,64,65,66,68,70Ga and stable isotope 69Ga were also expected to be generated mostly via (p,n) and (p,2n) reactions when natZn target was used in the 67Ga production. In contrast, radioactive 66Ga and 68Ga impurities were mainly produced following bombardment of enriched 67Zn and 68Zn targets.

Calculated Radioactivity Yields of Gallium-67 using Matlab Codes

In nuclear medicine, gallium-67 (67Ga) is potentially applied for imaging a certain type of tissue. In this investigation, 67Ga is theoretically studied in terms of its potential radioactivity yields at the end of various energetic proton bombardments. Nuclear cross-sections derived from the Talys Evaluated Nuclear Data Library (TENDL) 2017 were used as the input files, while a Matlab code was developed to perform the yield calculations of 67Zn(p,n)67Ga and 68Zn(p,2n)67Ga nuclear reactions to produce 67Ga. Two different targets – enriched 67Zn and natZn targets – were simulated in the calculations. The calculated yields suggested that a maximum of 27.37 MBq/µAh could be achieved when enriched 67Zn target was irradiated with 15-MeV protons, whereas 46.99 MBq/µAh could be generated following a 30 MeV proton bombardment of enriched 68Zn target. Various radioactive gallium impurities, i.e. 63,64,65,66,68,70Ga and stable 69Ga isotope were also expected to be generated mostly via (p,n) and (p,2n) reactions when natZn target was used in the 67Ga production. In contrast, radioactive 66Ga and 68Ga impurities were mainly produced following bombardment of enriched 67Zn and 68Zn targets. This study can be used as a reference for future 67Ga radionuclide production.

Medium Energy Carbon and Nitrogen Ion Beam Induced Modifications in Charge Transport, Structural and Optical Properties of Ni/Pd/n-GaN Schottky Barrier Diodes.

The irradiation effects of carbon and nitrogen medium energy ions (MEI) on charge transport, structural and optical properties of Ni/Pd/n-GaN Schottky barrier diodes are reported. The devices are exposed to 600 keV C2+ and 650 keV N2+ ions in the fluence range of 1 × 1013 to 1 × 1015 ions cm−2. The SRIM/TRIM simulations provide quantitative estimations of damage created along the trajectories of ion beams in the device profile. The electrical parameters like Schottky barrier height, series resistance of the Ni/Pd/n-GaN Schottky barrier diodes decreases for a fluence of 1 × 1013 ions cm−2 and thereafter increases with an increase in fluence of 600 keV C2+ and 650 keV N2+ ions. The charge transport mechanism is influenced by various current transport mechanisms along with thermionic emission. Photoluminescence studies have demonstrated the presence of yellow luminescence in the pristine samples. It disappears at higher fluences due to the possible occupancy of Ga vacancies. The presence of the green luminescence band may be attributed to the dislocation caused by the combination of gallium vacancy clusters and impurities due to MEI irradiation. Furthermore, X-ray diffraction studies reveal that there is a decrease in the intensity and shift in the diffraction peaks towards the lower side of two thetas. The reductions in the intensity of C2+ ion irradiation is more when compared to N2+ ion irradiation, which may be attributed to change in the mean atomic scattering factor on a given site for light C2+ ion as compared to N2+ ion.

Effect of homovalent Bi/Ga substitution on propagations of flaws, dislocations and crack in Bi-2212 superconducting ceramics: Evaluation of new operable slip systems with substitution

This study defines a strong methodology between the mechanical performance behaviors and formation of possible operable slip systems in the crystal structure of Bi-2212 superconducting phase with trivalent Bi/Ga substitution with the aid of Vickers hardness tests exerted at various indentation load intervals 0.245 N–2.940 N. It is found that the mechanical performance behaviors improve regularly with the increment in the trivalent Bi/Ga partial substitution level up to the value of x = 0.05 due to the formation of new operable slip systems. Namely, the optimum gallium (Ga) impurities serve as the strain fields and associated forces for the interaction of dislocations within the different orientations with each other to impose the surface residual compressive stresses orienting favorably the superconducting grains. Thus, the propagation of dislocations, flaws and cracks divert in the crystal structure. On this basis, the presence of optimum Ga impurity in the Bi-2212 crystal system strengthens the mechanical strength, critical stress, resistance to the plastic deformation, stiffness and durability nature. Moreover, the experimental results advance in-depth understanding of fundamental links between the porosity and Young's moduli of elasticity founded on the impurity level and applied test loads. It is observed that in case of the optimum level of x = 0.05 the propagation of flaws, dislocations and cracks proceed along the transgranular regions instead of the intergranular regions as a consequence of improvement in the durable tetragonal phase. On the other hand, the excess Ga content level in the polycrystalline Bi-2212 system results in the augmentation in the stress raisers, crack surface energy and crack-initiating flaws, activating the stress-induced phase transformation.

Origin of acceptor diffusion into silicon substrate during GaN growth by metal organic chemical vapor deposition

This study investigated the change in carrier concentration near the surface of a silicon substrate during gallium nitride (GaN) growth with an aluminum nitride (AlN) buffer layer. It was observed that aluminum, gallium, and carbon diffused into the silicon substrate during the growth process and that the carrier concentration increased with increasing concentration of aluminum and gallium impurities. The gallium that diffused into the silicon substrate was identified as having originated from the gallium that decomposed on the reactor wall during the growth process and the gallium introduced onto the silicon substrate during GaN growth. In contrast, the amount of aluminum that diffused into the substrate was influenced by the duration of the trimethylaluminum (TMAl) flow: a long duration of the TMAl flow step before AlN growth led to a high aluminum concentration near the substrate surface.

Preparation and Characterization of ZnO Thin Layers with Various Percentages of Gallium Impurities

In this study, thin films of pure ZnO and doped ZnO with different percentages of gallium (0.5, 1, 2 and 4vt. %) on the glass substrates were deposited by using sol-gel method via spin coating technique at 2500 rpm, and all layers were annealed at 200°C for 1h and then Were examined their electrical, optical and structural properties. Concentration of all solution was 0.1M. The results show that the optimized layer is 0.5% GZO. By examining the transmittance spectrums we find that by doping the transparency of samples were improved and all samples in the visible areas 400-800nm are transparent. The electrical conductivity of all samples has been measured by four-point probe technique. The electrical conductivitys of pure ZnO sample and 0.5% GZO are 910-5 S/cm and 110-4 S/cm respectively. It can be a good choice for optoelectronic applications. Also X-ray diffraction results showed that diffraction peaks of 0.5% GZO sample have a small changes towards lower angles compared to the diffraction peaks of ZnO.

Preparation and Characterization of ZnO Thin Layers with Various Percentages of Gallium Impurities

Preparation and Characterization of ZnO Thin Layers with Various Percentages of Gallium Impurities

Gallium hole traps in irradiated KTiOPO4:Ga crystals

Nominally pure and gallium doped single crystals of potassium titanyl phosphate (KTiOPO4) have been studied by Electron Paramagnetic Resonance at low temperatures before and after irradiation. Irradiation with 20 MeV electrons performed at room temperature and liquid nitrogen temperature caused an appearance of electrons and holes. Gallium impurities act as hole traps in KTiOPO4 creating Ga4+ centers. Two different Ga4+ centers were observed, Ga1 and Ga2. The Ga1 centers are dominant in Ga-doped samples. For the Ga1 center, a superhyperfine structure with one nucleus with nuclear spin ½ was registered and attributed to the interaction of gallium electrons with a phosphorus nucleus or proton in its surrounding. In both Ga1 and Ga2 centers, Ga4+ ions substitute for Ti4+ ions, but with a preference to one of two electrically distinct crystallographic positions (site selective substitution). The Ga doping eliminates one of the shortcomings of KTP crystals—ionic conductivity of bulk crystals. However, this does not improve significantly the resistance of the crystals to electron and γ-radiation.

Ab initio study of gallium stabilized δ-plutonium alloys and hydrogen–vacancy complexes

All-electron density functional theory was used to investigate δ-plutonium (δ-Pu) alloyed with gallium (Ga) impurities at 3.125, 6.25, 9.375 atomic (at)% Ga concentrations. The results indicated that the lowest energy structure is anti-ferromagnetic, independent of the Ga concentration. At higher Ga concentrations (>3.125 at%), the position of the Ga atoms are separated by four nearest neighbor Pu–Pu shells. The results also showed that the lattice constant contracts with increasing Ga concentration, which is in agreement with experimental data. Furthermore with increasing Ga concentration, the face-centered-cubic structure becomes more stably coupled with increasing short-range disorder. The formation energies show that the alloying process is exothermic, with an energy range of −0.028 to −0.099 eV/atom. The analyses of the partial density of states indicated that the Pu–Ga interactions are dominated by Pu 6d and Ga 4p hybridizations, as well as Ga 4s–4p hybridizations. Finally, the computed formation energies for vacancy and hydrogen–vacancy complexes within the 3.125 at% Ga cell were 1.12 eV (endothermic) and −3.88 eV (exothermic), respectively. In addition, the hydrogen atom prefers to interact much more strongly to the Pu atom than the Ga atom in the hydrogen–vacancy complex.

Optical transitions of holes in uniaxially compressed germanium

Spontaneous emission and photoconductivity of germanium with gallium impurity are studied for determining the energy spectrum of hole states in this material in which radiation can be induced as a result of transitions of holes between these states. Holes were excited by electric field pulses with a strength up to 12 kV/cm at T = 4.2 K under uniaxial compression of samples up to 12 kbar. It has been found that hole emission spectra for transitions between resonant and local states of the impurity have a structure identical to the photoconductivity and absorption spectra. Transitions from resonance states, which are associated with the heavy hole subband, have not been detected. It has been found that in an electric field lower than 100 V/cm, a compressed crystal emits as a result of transitions of heavy holes. In a strong electric field (1–3 kV/cm), emission is observed in the energy range up to 140 meV, and transitions with emission of TA and LO phonons appear in such a field. The emission spectra under pressures of 0 and 12 kbar differ insignificantly. Hence, it follows that the contributions from heavy and light holes in a strong electric field are indistinguishable.

Electrochemical Deposition of Compact and Nanostructured Doped ZnO Films

This study reviews the electrodeposition of compact films and ZnO nanostructures doped with aluminum, gallium and indium. Electrodeposition in an aqueous perchlorate media favored the formation of relatively compact films with highly preferred orientation along the c-axis. By means of impedance measurements it was able to determine the doping level of each sample. Changing the aqueous perchlorate media to a sulfate one favored the formation of lamellar nanostructures, which did not affect the incorporation of aluminum and gallium impurities. Morphology, optical and crystallographic properties of these films for possible application in fields such as photovoltaics and photocatalysis are analyzed.

Relaxation of the shallow acceptor center in germanium

Polarized negative muons were used to study relaxation mechanisms of shallow acceptors in germanium. In p-type germanium at low temperatures relaxation of the muon spin was observed, indicating that the muonic atom (gallium-like acceptor center) formed via capture of the negative muon by a host atom is in the paramagnetic state and its magnetic moment is relaxing. The relaxation rate of the muon spin was found to depend on temperature and on concentration of gallium impurity. We conclude that to the relaxation of the magnetic moment of the Ga acceptor in Ge there contribute both scattering of phonons and quadrupole interaction between the acceptors. We estimate, for the first time, the hyperfine interaction constant for the gallium acceptor in germanium as 0.11 MHz.

Impurity complexes and conductivity of Ga-doped ZnO

Using hybrid functional theory together with experimental measurements, we investigate the influence of gallium impurities and their complexes on electrical properties of ZnO. In contrast to the behavior of isolated Ga impurities and native defects, the calculated formation energies of Ga complexes are consistent with our experimental data. We show that for high levels of Ga doping the acceptor behavior of Ga${}_{\mathrm{Zn}}$-${V}_{\mathrm{Zn}}$ and Ga${}_{\mathrm{Zn}}$-O${}_{i}$ complexes explains the conductivity measurements and compensation levels in ZnO. The computed binding energies of these complexes are also consistent with the binding energies obtained from the measurements of the temperature dependence of carrier mobility. Our results show that the formation of defect complexes, often overlooked by theory, can be indispensable in capturing the defect physics.

Combined reprocessing of weapons plutonium into high-purity oxide fuel

The main results of a study of regimes for dissolution of plutonium oxide and mononitride powders, obtained by the pyrochemical method from weapons plutonium, in acids for subsequent extraction removal of gallium, americium, and ballast impurities and obtaining ceramic-type plutonium oxide powder suitable for fabricating mixing oxide fuel are presented. It is established experimentally that plutonium oxide and mononitride obtained by the pyrochemical method dissolve rapidly in the acid mixture HNO 3 12 moles/liter and HF 0.1 moles/liter. Plutonium extraction into solution reaches >99%.

Field emission and optical properties of Ga-doped ZnO nanowires synthesized via thermal evaporation

Ga-doped ZnO (GZO) nanowires have been synthesized by thermal evaporation with gallium metal as the dopant source. The morphology, microstructure and chemical composition were determined by field emission scanning electron microscopy (FE-SEM), X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS). The investigation confirmed that the GZO nanowires were the wurtzite hexagonal structures. These doped nanowires have diameters in the range 30–70nm and lengths of several hundreds of nanometers with growth direction along the (100) crystal plane. The optical properties from the cathodoluminescence (CL) and photoluminescence (PL) spectrum show that GZO nanowires exhibit a relative weak ultraviolet emission (UV) and a strong green emission. The UV emission for ZnO and GZO nanowires is attributed to near band-edge emission from recombination of free excitons. Furthermore, the green emission is attributed to oxygen vacancy and gallium impurity energy levels. Field emission measurements demonstrate that the GZO possesses good performance with a turn-on field of 3.4V/μm at a current density of 10μA/cm2, a threshold field of 5.4V/μm at a current density of 1mA/cm2, and a field-enhancement factor β of 5945. These results are very helpful for the design, fabrication and optimization of integrated optoelectronic nanodevices using GZO nanowires.

Resonance states of gallium impurity in uniaxially compressed germanium

To identify optical transitions that can excite long-wavelength stimulated radiation in uniaxially compressed Ga-doped germanium, the absorption and photoconduction spectra of this material were studied over a wide range of pressures in the [111] and [001] directions. It was found that some of the excited states of gallium impurity became resonant upon the buildup of pressure. The energy levels of these states reach the light-hole band, whereupon they enter this band and remain near its edge, showing up in the form of broad bands. No singularities confirming the existence of the impurity resonance states were observed in the spectra near the edge of the heavy-hole band.

Segregation Behavior of Impurities in Gallium during Directional Solidification

The effective solid–liquid segregation coefficients of impurities in Ga were measured in binary and multicomponent gallium–impurity (Sn, In, Cu, Ge, Ag) systems. The results demonstrate that the introduction of Sn into both binary and multicomponent systems notably increases the effective segregation coefficients of the other impurities. The likely reason is that the presence of Sn leads to the formation of linear and planar defects, which gives rise to nonequilibrium impurity trapping by the growing gallium crystal.

Radiation damage and its recovery in focused ion beam fabricated ferroelectric capacitors

We studied the effect of ion damage on the properties of 50 keV Ga+ focused ion beam fabricated lead-zirconate-titanate capacitors as a function of the ion dose. We observed significant modification in the chemical composition of the damaged layer due to loss of lead and oxygen, and gallium impurity accumulation. The 5–10 nm thick damaged layer becomes dielectric after annealing and does not recover its ferroelectric properties. This dielectric layer substantially reduces the actual volume of the ferroelectric material in sub-100 nm structures, and can affect their performance.

A new class of holographic materials based on semiconductor CdF2 crystals with bistable centers. Part II. Growth of optically perfect crystals

The crystal-chemical processes occurring during the growth of cadmium fluoride crystals doped with bistable gallium and indium impurities and during conversion of the crystals to the semiconductor state are considered. It is found that doping with indium does not strongly affect the optical performance of the crystals, while gallium, due to its low solubility in cadmium fluoride, strongly impairs this performance. It is shown that co-doping of the crystals with highly soluble impurities (yttrium, scandium, and gadolinium fluorides) makes it possible to obtain optically perfect gallium-doped crystals.