Low Ga Research Articles

Effects of Ga Doping Concentration on Morphological and Optical Properties of Hydrothermally Grown ZnO Nanorods

Abstract Zinc oxide nanorods (ZnO NRs) provide great potential as an electron transporting material (ETM) in solar cells due to their advantages of high light transmission, ease of synthesis at low temperature, and high electron mobility. By adding gallium (Ga) atom into ZnO crystal structure, semiconducting properties can be improved. In this work, effects of Ga incorporation into ZnO NRs on morphology, crystal structure, and optical properties were investigated. The ZnO nanorods were grown on a seed layer via hydrothermal method at temperature of lower than 100°C. Four concentrations (1 ,2 ,3 and 4 atom%) of Ga dopants in aqueous precursor solution were carried out. Ammonia solution were also added to make a neutral pH value. It was found that, for the sample without additive ammonium solution, the diameter of NRs and energy band gap increases slightly with increasing Ga doping atom%. However, the NRs prepared with additive ammonium solution show no significant change in diameter and energy band gap. X-ray diffraction (XRD) analysis indicated that preparation with ammonium solution has high ZnO growth rate but low Ga incorporation possibility. Therefore, the crystal size of NRs prepared with ammonium solution became larger. For the samples synthesized without ammonium solution, the crystal size increases systematically with adding Ga concentration. Finally, Ga incorporation into ZnO crystal is possible for the conventional preparation without ammonium solution.

Molecular beam epitaxial growth of high quality Ga-catalyzed GaAs1–xSbx(x > 0.8) nanowires on Si (111) with photoluminescence emission reaching 1.7 μm

The advancement of ternary GaAsSb mismatched alloy system toward the Sb-rich corner of the phase diagram in the nanowire (NW) configuration on silicon remains a challenge. A large lattice mismatch between the silicon substrate and GaAsSb with an Sb-rich composition, along with the low supersaturation and low solubility of Sb in the Ga droplet in the vapor–liquid–solid growth mechanism, causes significant issues during Ga-assisted molecular beam epitaxial growth of these NWs. In this work, we have carried out a systematic study of Sb-rich GaAs1–xSbx NWs grown on Si (111) using variations of the Ga, As, and Sb beam equivalent pressures (BEP) to minimize undesirable parasitic growth and achieve photoemission up to 1.7 μm. Ga-assisted molecular beam epitaxy is the enabling growth technology for the growth of these self-catalyzed GaAs1–xSbx (x > 0.8) NWs. The use of a dual substrate temperature approach along with low As background pressure and a low Ga BEP were found to be the key growth components in achieving a well-faceted NW morphology with a low parasitic layer on the substrate. Energy-dispersive x-ray spectroscopy analysis confirms uniform compositional homogeneity along the NWs, while selected-area electron diffraction patterns in the transmission electron microscope revealed a zinc-blende crystal structure. A peak μ-photoluminescence emission of 1680 nm with a narrow FWHM was obtained at 4 K. Raman spectra at room temperature exhibit only GaSb related LO and TO modes, which attest to the high quality of the NWs grown. This is a promising approach due to the broad scope of applicability to grow other mismatched alloy material systems in a NW configuration.

Direct Electrodeposition of Ga and the Simultaneous Production of NaOH and NaHCO3 from Carbonated Spent Liquor by Membrane Electrolysis

The direct electrodeposition of Ga from carbonated spent liquor is proposed by membrane electrolysis with the simultaneous production of NaOH and NaHCO3. The effects of electrolysis time, current density, and mechanical agitation on current efficiency (CE) are studied. Metallic Ga is successfully electrodeposited from synthetic liquor with a very low Ga concentration by using a Ga-coating cathode. The current efficiency for NaOH production decreases with the electrolysis time. After 13 h of electrolysis, the concentration of NaOH rose to 109 g L–1. The current efficiency for NaHCO3 production is almost constant in the first 8 h, and the value is about 74%. Then, the current efficiency decreases rapidly due to the accelerated formation of CO2. The largest concentration of NaHCO3 is about 108 g L–1. Ga electrodeposition is affected obviously by an additive (FC-95), the current density, and mechanical agitation. In carbonated spent liquor, 97.9% of Ga can be electrochemically extracted.

Low gallium‐content, dysprosium III‐doped, Ge–As–Ga–Se chalcogenide glasses for active mid‐infrared fiber optics

AbstractA systematic investigation is presented, for the first time, of a 1000 ppmw (parts per million, by weight) Dy3+‐doped Ge–As–Ga–Se chalcogenide glass series, with a fixed low Ga content of 1 atomic% (at. %), suitable for active mid‐infrared fiber optics. Seven glasses constitute the series, which have increasing average coordination number from 2.49 to 2.61, in steps of 0.02, with the GeSe2, As2Se3, and Ga2Se3 stoichiometries kept. Glass formation is confirmed using X‐ray diffraction and differential scanning calorimetry. Fourier transform infrared spectroscopy is reported for the series. Parallel plate viscometry enables prediction of fiber‐drawing temperatures and, with differential thermal analysis, determines the potential for fiber fabrication. X‐ray diffraction of samples after parallel‐plate viscometry shows that Ge25As9Ga1Se65 (at. %) alone, in the glass‐series, devitrifies to form the single‐crystalline phase: monoclinic‐GeSe2; scanning electron microscope imaging suggests that this phase is both surface and bulk grown. Overall, the recommended host glass at. % compositions for doping with rare‐earth ions and drawing to active mid‐infrared fiber are: Ge17.5As18Ga1Se63.5, Ge15As21Ga1Se63, and Ge12.5As24Ga1Se62.5.

Expansion and diversification of the gibberellin receptor GIBBERELLIN INSENSITIVE DWARF1 (GID1) family in land plants

Here we uncover the major evolutionary events shaping the evolution of the GID1 family of gibberellin receptors in land plants at the sequence, structure and gene expression levels. Gibberellic acid (gibberellin, GA) controls key developmental processes in the life cycle of land plants. By interacting with the GIBBERELLIN INSENSITIVE DWARF1 (GID1) receptor, GA regulates the expression of a wide range of genes through different pathways. Here we report the systematic identification and classification of GID1s in 54 plants genomes, encompassing from bryophytes and lycophytes, to several monocots and eudicots. We investigated the evolutionary relationship of GID1s using a comparative genomics framework and found strong support for a previously proposed phylogenetic classification of this family in land plants. We identified lineage-specific expansions of particular subfamilies (i.e. GID1ac and GID1b) in different eudicot lineages (e.g. GID1b in legumes). Further, we found both, shared and divergent structural features between GID1ac and GID1b subgroups in eudicots that provide mechanistic insights on their functions. Gene expression data from several species show that at least one GID1 gene is expressed in every sampled tissue, with a strong bias of GID1b expression towards underground tissues and dry legume seeds (which typically have low GA levels). Taken together, our results indicate that GID1ac retained canonical GA signaling roles, whereas GID1b specialized in conditions of low GA concentrations. We propose that this functional specialization occurred initially at the gene expression level and was later fine-tuned by mutations that conferred greater GA affinity to GID1b, including a Phe residue in the GA-binding pocket. Finally, we discuss the importance of our findings to understand the diversification of GA perception mechanisms in land plants.

Compositional dependence of physical and structural properties in (Ge1−xGax)S2 chalcogenide glasses

Glassy and partially crystallized samples of (Ge1−xGax)S2 (0 mol% ≤ x ≤ 50 mol%) were prepared and investigated for the Ga effect on their physical and structural properties. For low Ga content (0 mol% ≤ x ≤ 30 mol%), homogeneous glassy samples were prepared and present good physical properties, such as high glass transition temperature (>400 °C) and Vickers hardness (>2.60 GPa). With the Ga substitution for Ge, the thermal stability of samples decreases, leading to the precipitation of α-Ga2S3 crystallites when x > 40 mol%. Structural evolution of (Ge1−xGax)S2 samples was investigated by Raman spectra and X-ray diffraction techniques. The correlation between the physical properties and structural evolution was established.

Ga-doped ZnO films magnetron sputtered at ultralow discharge voltages: Significance of controlling defect generation

In magnetron sputtered oxide thin films, both the structure and physical properties are affected by bombardment-induced defects and their annihilation. Ga-doped zinc oxide (GZO) films with low Ga content (~1.7 at.%) were magnetron sputtered at various discharge voltages (70–220 V) and the growth temperatures (130 °C and 380 °C). The microstructure was characterized by X-ray Diffractometry, Raman Spectroscopy, and Transmission Electron Microscopy. Meanwhile, the electrical and optical properties were measured by Hall-effect measurement and Spectroscopic Ellipsometry, respectively. We found that reducing the discharge voltage led to higher structural quality and better electrical properties, independent of the growth temperature. The benefit, from using a high temperature (i.e., 380 °C), of the structural improvement, can only be achieved when the discharge voltage has been decreased to ultralow (i.e., 70 V). Our results suggest that for high quality GZO films deposition, controlling the defect generation should be preferable to simply increasing the growth temperature.

Formation of self-assembled GaAs quantum dots via droplet epitaxy on misoriented GaAs(111)B substrates

Self-assembled GaAs quantum dots (QDs) have been grown on misoriented GaAs(111)B substrates using droplet epitaxy. Different droplet deposition temperatures, arsenization temperatures and times as well as postcrystallization annealing temperatures have been investigated, while the amount of deposited Ga was kept constant at two monolayers. Atomic force microscopy measurements reveal that unusually low Ga deposition and arsenization temperatures in comparison to the (100) and (111)A surfaces are necessary to obtain droplet/QD densities in the order of 108 cm−2. The formation of droplets and their crystallization result in QDs with approximately circular symmetry regardless of the anisotropy introduced by the miscut. Crystallized GaAs QDs show the thermal resistance comparable to those observed on (100) and (111)A. When the QDs are embedded in Al0.3Ga0.7 As, a spectrally broad luminescence around 790 nm can be observed.

A Novel Low Complexity GA Based PTS Method for PAPR Reduction in OFDM Systems

A Novel Low Complexity GA Based PTS Method for PAPR Reduction in OFDM Systems

Impaired cognitive ability at 2.5years predicts later visual and ophthalmological problems in children born very preterm.

To identify possible predictive factors for visual problems at 6.5years in children born very preterm. During 2004-2007, all very preterm infants (gestational age [GA] <32weeks) in Uppsala County, Sweden were screened for retinopathy of prematurity (ROP) neonatally; at four months, visual tracking was tested; at 2.5years, visuospatial and cognitive tests were carried out. At 6.5years, 84 preterm children and a reference group of 64 full-term children underwent ophthalmological testing. Mean visual acuity (VA) did not differ between the groups, but subnormal VA (≤0.8) was more common in the preterm group (31% vs 14%; p<0.05). More often than full-term children, preterm children had impaired contrast sensitivity (<0.5) (36% vs 19%; p<0.05) and strabismus (8% vs 0%; p<0.05). Low GA, ROP, intraventricular haemorrhage 3-4/periventricular leukomalacia and cognitive disability at 2.5years predicted ophthalmological and visual problems at 6.5years. Visual tracking ability at four months was not predictive of ophthalmological outcome. Children born preterm had more ophthalmological problems at 6.5years of age, including subtle dysfunctions. ROP, early brain injury and impaired cognitive function around 2.5years predicted later ophthalmological dysfunctions.

Effect of guanidinium on the optical properties and structure of the methylammonium lead halide perovskite

The stability and performance of perovskite-based solar cells can be improved by changing the nature of the organic cation. Herein, mixed methylammonium–guanidinium perovskites (MA1-xGAxPbI3) are structurally and optically characterized. The Pawley fit method confirmed the formation of the iodide halide GAPbI3 tetragonal phase (P42_NMC). Up to 20% of the guanidinium cation was incorporated in the methylammonium lead iodide perovskite, producing a lattice enlargement, which was investigated studying the shift of the diffraction peaks of the MAPbI3 (I4_CM) tetragonal lattice. Long-term stability was tested, resulting in improved mixed perovskites with a low GA content. The bandgap shifted to lower energies. The absorption bandgap diminished slightly when the GA cation substituted up to 20% of MA in MAPbI3, degrading when the GA amount in the mixed perovskite is larger. FESEM morphological analysis was performed showing that a uniform thin film was deposited. PL studies showed that only shallow defects had been introduced.

Comparative study of image contrast in scanning electron microscope and helium ion microscope.

Images of Ga+ -implanted amorphous silicon layers in a 110 n-type silicon substrate have been collected by a range of detectors in a scanning electron microscope and a helium ion microscope. The effects of the implantation dose and imaging parameters (beam energy, dwell time, etc.) on the image contrast were investigated. We demonstrate a similar relationship for both the helium ion microscope Everhart-Thornley and scanning electron microscope Inlens detectors between the contrast of the images and the Ga+ density and imaging parameters. These results also show that dynamic charging effects have a significant impact on the quantification of the helium ion microscope and scanning electron microscope contrast.

Double band gap gradients in sequentially processed photovoltaic absorbers from the Cu(In,Ga)Se2‐ZnSe pseudobinary system

AbstractWide band gap Cu(In,Ga)Se2‐ZnSe (CIGZSe) thin films have been synthesized using a sequential process, with the objective to demonstrate the possibility to tune the band gap and introduce double gradients playing with the content of Ga at the back and Zn at the front. In a first approach, we start by varying the 3‐valent cationic composition of the system, and then we modify the reactive annealing conditions in order to understand and control the elemental gradients. Structural, compositional, and morphological properties of the corresponding absorbers were analysed by X‐ray diffraction, Raman spectroscopy, energy dispersive spectrometer, Auger spectroscopy, and scanning electron microscopy. Solar cells were fabricated and characterized, focusing on the identification of the most promising cationic composition. The compounds from the complex Cu(In,Ga)Se2‐ZnSe system can adopt either the chalcopyrite or sphalerite phases depending on the [Zn]/[metals] and [Ga]/([Ga] + [In]) ratios. We demonstrate that Ga naturally diffuses towards the back region forming a Ga‐rich, wide band gap chalcopyrite phase at the rear contact, as is commonly observed for a Cu(In,Ga)Se2 synthesized via selenization process. On the contrary, Zn is preferably accumulated at the surface, forming wide band gap sphalerite Cu(In,Ga)ZnSe3 phases with high Zn and very low Ga contents at the surface. This opens an additional way to control the surface's band gap. With this approach, the formation of a doubly graded band gap profile with Ga‐rich layers at the back and Zn‐rich layers at the front is demonstrated in a single selenization step, showing promising efficiency and open circuit voltage values (up to 6.7% and 709 mV, respectively).

Terahertz conductivity of the highly mismatched amorphous alloy, GaNBi

We report terahertz optical conductivity measurements of the highly mismatched alloy, GaNBi. We find that in these amorphous GaNBi epilayers grown using plasma assisted molecular beam epitaxy, the optical conductivity is enhanced in the samples grown at higher gallium beam equivalent pressure (BEP). The optical conductivity spectra in these pseudo-amorphous epilayers follow a Drude–Smith behaviour due to charge confinement effects. The direct current conductivity in the epilayers grown at the highest Ga BEP (3.1 × 10−7 Torr) show an increase of three orders of magnitude compared to the one grown at the lowest Ga BEP (2.0 × 10−7 Torr). Our measurements suggests a percolative transition from an insulating nature in the GaNBi epilayers grown at low Ga BEP to a highly conducting phase in the epilayers grown at high Ga BEP.

Electronic transport properties of graphene doped by gallium

In this work we present the effect of low dose gallium (Ga) deposition (<4 ML) performed in UHV (10−7 Pa) on the electronic doping and charge carrier scattering in graphene grown by chemical vapor deposition. In situ graphene transport measurements performed with a graphene field-effect transistor structure show that at low Ga coverages a graphene layer tends to be strongly n-doped with an efficiency of 0.64 electrons per one Ga atom, while the further deposition and Ga cluster formation results in removing electrons from graphene (less n-doping). The experimental results are supported by the density functional theory calculations and explained as a consequence of distinct interaction between graphene and Ga atoms in case of individual atoms, layers, or clusters.

Ga-doped ZnO films by magnetron sputtering at ultralow discharge voltages: Effects of defect annihilation

Preparation of high quality transparent conductive oxide (TCO) films by sputter deposition involves an intricate balance of defect generation by the highly energetic negative oxygen ions (depending on the discharge voltage) and the concomitant annihilation of these defects during film growth. Ga-doped ZnO films with a low Ga content (1.7at.%) were deposited to investigate the effects of defect annihilation on the microstructure evolutions as well as the optical and electrical properties. To achieve this aim, we prepared the GZO films by magnetron sputtering at ultralow discharge voltages (~70V) to minimize the defect generation, and varied the substrate temperature (from 130°C to 380°C) to adjust the annihilation rates. The microstructure was systematically characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and Raman Spectroscopy. The electrical and optical properties were obtained by a Hall-effect measurement system and Spectroscopic Ellipsometry (SE), respectively. It was found that (i) even under the condition of highly controlled defect generation from the bombardment of negative oxygen ions, a sufficient annihilation of the defects cannot be realized without externally heating the substrate; and (ii) there existed a threshold temperature, above which both the structural quality and the electrical properties were improved with the increased temperature over the temperature range we examined. These results reveal that the growth temperature during the GZO film deposition has played an important role in effective annihilation of the irradiation-induced structural defects, which may be due to the higher diffusion barrier of Ga atoms in our GZO films.

Abnormal Endogenous Repression of GA Signaling in a Seedless Table Grape Cultivar with High Berry Growth Response to GA Application.

Gibberellin (GA) application is routinely used in the table grape industry to increase berry size and cluster length. Although grapevine cultivars show a wide range of growth responsiveness to GA3 application, the reasons for these differences is unclear. To shed light on this issue, two commercial grapevine cultivars with contrasting berry response to GA were selected for comparative analysis, in which we tested if the differences in response: (1) is organ-specific or cultivar-related; (2) will be reflected in qualitative/quantitative differences in transcripts/proteins of central components of GA metabolism and signaling and levels of GA metabolites. Our results showed that in addition to the high response of its berries to GA, internodes and rachis of cv. Black finger (BF) presented a greater growth response compared to that of cv. Spring blush (SB). In agreement, the results exposed significant quantitative differences in GA signaling components in several organs of both cultivars. Exceptionally higher level of all three functional VvDELLA proteins was recorded in young BF organs, accompanied by elevated VvGID1 expression and lower VvSLY1b transcripts. Absence of seed traces, low endogenous GA quantities and lower expression of VvGA20ox4 and VvGA3ox3 were also recorded in berries of BF. Our results raise the hypothesis that, in young organs of BF, low expression of VvSLY1b may be responsible for the massive accumulation of VvDELLA proteins, which then leads to elevated VvGID1 levels. This integrated analysis suggests causal relationship between endogenous mechanisms leading to anomalous GA signaling repression in BF, manifested by high quantities of VvDELLA proteins, and greater growth response to GA application.

A-plane GaN growth on (11-20) 4H-SiC substrate with an ultrathin interlayer

A-plane GaN was attempted to be grown on (11-20) 4H-SiC bulk substrate without using a traditional thick buffer layer. By inducing TMAl treatment before the GaN growth step and using both a low pressure and V/III ratio, the interlayer thickness of the a-plane GaN/SiC was reduced to 1.7+0.5nm. The ultrathin interlayer was observed to be either AlN or AlGaN with a low Ga composition. This study is aimed to contribute to the understanding of GaN growth on the sidewalls of c-plane trench structure SiC. The ultrathin growth technique is also hoped to be applied to the fabrication of GaN-based vertical structure nonpolar optical or electrical devices.

Thermal ionization and thermally activated crossover quenching processes for5d−4fluminescence inY3Al5−xGaxO12:Pr3+

We investigated thermally activated ionization and thermally activated crossover as the two possibilities of quenching of $5d$ luminescence in $\mathrm{P}{\mathrm{r}}^{3+}$-doped ${\mathrm{Y}}_{3}\mathrm{A}{\mathrm{l}}_{5\ensuremath{-}x}\mathrm{G}{\mathrm{a}}_{x}{\mathrm{O}}_{12}$. Varying the Ga content $x$ gives the control over the relative energy level location of the $5d$ and $4{f}^{2}:^{3}P_{J}$ states of $\mathrm{P}{\mathrm{r}}^{3+}$ and the host conduction band (CB). Temperature-dependent luminescence lifetime measurements show that the $5d$ luminescence quenching temperature ${T}_{50%}$ increases up to $x=2$ and decreases with further increasing Ga content. This peculiar behavior is explained by a unique transition between the two quenching mechanisms which have an opposite dependence of thermal quenching on Ga content. For low Ga content, thermally activated crossover from the $4f5d$ state to the $4{f}^{2}(^{3}P_{J})$ states is the operative quenching mechanism. With increasing Ga content, the activation energy for thermally activated crossover becomes larger, as derived from the configuration coordinate diagram, while from the vacuum referred binding energy diagram the activation energy of thermal ionization becomes smaller. Based on these results, we demonstrated that the thermal quenching of $\mathrm{P}{\mathrm{r}}^{3+}:5{d}_{1}\ensuremath{-}4f$ luminescence in ${\mathrm{Y}}_{3}\mathrm{A}{\mathrm{l}}_{5\ensuremath{-}x}\mathrm{G}{\mathrm{a}}_{x}{\mathrm{O}}_{12}$ with $x=0,\phantom{\rule{0.28em}{0ex}}1,\phantom{\rule{0.28em}{0ex}}2$ is a thermally activated crossover while for $x=3,\phantom{\rule{0.28em}{0ex}}4,\phantom{\rule{0.28em}{0ex}}5$ it results from the thermal ionization.

掺杂(Al&lt;sup&gt;3+&lt;/sup&gt;,Ga&lt;sup&gt;3+&lt;/sup&gt;)对石榴石型电解质Li&lt;sub&gt;7-x&lt;/sub&gt;La&lt;sub&gt;3&lt;/sub&gt;Zr&lt;sub&gt;2-x&lt;/sub&gt;Ta&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt;锂离子电导率的影响

为了提高Li7−xLa3Zr2−xTaxO12(LLZTO)固体电解质电导率，本文研究了Al3+和Ga3+掺杂对材料性能的影响。结果表明，掺杂Al3+和Ga3+，显著提高了材料的致密度和电导率。Al-Li7−xLa3Zr2−xTaxO12(Al-LLZTO)中的铝离子同时存在于晶粒和晶界中，晶界中的铝含量是晶粒中的两倍，Al-Li6.4La3Zr1.4Ta0.6O12拥有最高的总电导率0.54 mS/cm，其激活能为0.42 eV。Li7−x−3yGayLa3Zr2−xTaxO12(Ga-LLZTO)中，铝的含量较低，镓离子同时存在于电解质的晶粒与晶界中。在锂含量相同的样品中，Ga-LLZTO的总电导率要高于Al-LLZTO，表明Ga的掺杂比Al的掺杂对LLZTO电解质的电导率提升更大。最终，我们得到总电导率最高的样品Li6.4Ga0.1La3Zr1.7Ta0.3O12，其总电导率和激活能分别为0.87 mS/cm和0.33 eV。 To obtain highly conductive Li7−xLa3Zr2−xTaxO12 (LLZTO) electrolytes, the influence of Al and Ga on them were investigated. The Al and Ga have been demonstrated to be supervalent dopants that stabilize cubic garnetof Li7La3Zr2O12 (LLZO) electrolytes. They are also sintering-aided compositions, increasing the overall conductivity of LLZO electrolytes. The results show that all the obtained electrolytes are cubic. The densification and conductivity of the LLZTO electrolyte were improved by Al or Ga inclusion. In the Al-Li7−xLa3Zr2−xTaxO12 (Al-LLZTO) electrolytes, Al was found in the grains and grain boundaries, but the Al content in the grain boundaries is about twice of that in the grains. The overall conductivity was optimized to 0.54 mS/cm with an activation energy of 0.42 eV for the Al-Li6.4La3Zr1.4Ta0.6O12 sample. In theLi7−x−3yGayLa3Zr2−xTaxO12 (Ga-LLZTO) electrolytes, the Al in a low conent and Ga were found in grains and grain boundaries. The overall conductivities of Ga-LLZTO electrolytes were higher than that of the Al-LLZTO electrolytes with almost the same nominal Li-content. Finally, the highest overall conductivity of 0.87 mS/cm with a low activation energy of 0.33 eV was achieved for the Li6.4Ga0.1La3Zr1.7Ta0.3O12 sample.