Increasing Ga Content Research Articles

Solution-Processed Ga-Doped ZnO Nanorod Arrays as Electron Acceptors in Organic Solar Cells

This paper reports the utilization of ZnO nanorod arrays (NRAs) doped with various concentrations of Ga (0, 0.5, 1, 2, and 3 at %) as electron acceptors in organic solar cells. The donor, poly(3-hexylthiophene) (P3HT), was spin coated onto Ga-doped ZnO NRAs that were grown on fluorine-doped tin oxide (FTO) substrates, followed by the deposition of a Ag electrode by a magnetron sputtering method. Adjusting the Ga precursor concentration allowed for the control of the structural and optical properties of ZnO NRAs. The short circuit current density increased with increasing Ga concentration from 0 to 1 at %, mainly because of improved exciton dissociation and increased charge extraction. Meanwhile, the reduced charge recombination and lower hole leakage current led to an increase in the open circuit voltage with Ga concentrations up to 1 at %. The device with the optimum Ga concentration of 1 at % exhibited power conversion efficiency nearly three times higher compared to the device without Ga doping. This finding suggests that the incorporation of Ga can be a simple and effective approach to improve the photovoltaic performance of organic solar cells.

Curcumin loaded poly (lactic-co-glycolic) acid nanofiber for the treatment of carcinoma

Poly (dl-lactic-co-glycolic) acid [PLGA] copolymers with different ratios (78/22, 68/32 and 61/39) and molecular weight (15,400, 11,000 and 10,000Da) were synthesized and characterized by 1H NMR, FTIR, GPC and TGA-DTA studies. Curcumin loaded PLGA with the size of 100–300nm were obtained by electrospinning in which no visible aggregation observed on the surface. The diameter of CPNF (61/39) nanofiber obtained from the topographical imaging by AFM is 160±10nm. The water contact angle measurements indicate that an increase in GA content results in increase in the hydrophilicity of the PLGA copolymer. The in vitro release profile and release kinetics from the CPNF demonstrated a sustained release of curcumin from CPNF. The release profile follows Korsmeyer–Peppas model suggesting a combination of surface drug dissolution and non-Fickian diffusion as a major drug release mechanism. The effect of CPNF on cell viability was assessed by the MTT (3-[4,5-dimethylthiazol-2-yl] 2,5-diphenyltetrazolium bromide) assay to examine the cytotoxic effect of released curcumin on A431 cells in vitro.

Single crystal Fe1−xGax thin films for monolithic microwave devices

Modern, high frequency, microwave devices for communications technologies can be made with thin ferromagnetic films with narrow microwave resonance linewidths. Recently, there has been interest in magnetostrictive materials where the material constants can change substantially with stresses and applied magnetic fields. We report the development of single crystal thin (20 nm thick) magnetostrictive films of Fe1−xGax (x = 0.20 FeGa(A), 0.23 FeGa(B), 0.28 FeGa(C) on GaAs(001) substrates and on their use in prototype microwave devices. These Galfenol films have a narrower linewidth than any previously reported similar thin films. We fabricate and characterize novel microstrip-based monolithic microwave devices using Galfenol thin films as an active element. We find a number of important features: (1) There is a large absorption (up to 30 dB/cm) at the resonance frequency. (2) The linewidth of the device is narrow ∼1.5 GHz. (3) The saturation magnetization of the samples decreases with the increase in Ga contents. (4) The cubic anisotropy is close to zero (∼0.06 kOe for FeGa(A)) and becomes negative for higher concentration of Ga content in the samples, and (5) the damping increases with increase in Ga concentration.

Structural and electronic properties of [formula omitted][formula omitted] (R = Ce and La) compounds

The compounds from CePd2Al2-xGax series were studied by means of magnetization and electrical resistivity measurements. The electrical resistivity was measured also on LaPd2Al2-xGax counterparts. The development of structural phase transition with Ga content was investigated and its connection with presence of vibron states was discussed. The structural parameters of CePd2Ga2 were determine for both tetragonal and triclinic structure from powder neutron diffraction data. All studied compounds order antiferromagnetically, the Néel temperature slightly decreases with increasing Ga content. Simultaneously, ferromagnetic correlations are observed in the series and become stronger with Ga concentration. The powder neutron diffraction on CePd2Ga2 proved the antiferromagnetic ground state, which is suppressed by magnetic field of 5T. We found several possible propagation vectors describing observed magnetic reflection.

Thermoelectric Properties of Ca3Co4-x Ga x O9+δ Prepared by Thermal Hydro-decomposition

The polycrystalline samples of Ca3Co4-xGaxO9+δ (0 ≤ x ≤ 0.15) were prepared by a simple thermal hydro-decomposition method. The high density ceramics were fabricated using a spark plasma sintering technique. The crystal structure of calcined powders was characterized by x-ray diffraction. The single phase of Ca3Co4-xGaxO9+δ was obtained. The scanning electron micrograph illustrated the grain alignment perpendicular to the direction of the pressure in the sintering process. The evidence from x-ray absorption near edge spectra were used to confirm the oxidation state of the Ga dopant. The thermoelectric properties of the misfit-layered of Ca3Co4-xGaxO9+δ were investigated. Seebeck coefficient tended to decrease with increasing Ga content due to the hole-doping effect. The electrical resistivity and thermal conductivity were monotonically decreased with increasing Ga content. The Ga doping of x = 0.15 showed the highest power factor of 3.99 × 10-4 W/mK2 at 1,023 K and the lowest thermal conductivity of 1.45 W/mK at 1,073 K. This resulted in the highest ZT of 0.29 at 1,073 K. From the optical absorption spectra, the electronic structure near the Fermi level show no significant change with Ga doping.

Effects of Ga concentration on the structural, electrical and optical properties of Ga-doped ZnO thin films grown by sol-gel method

Undoped ZnO and Ga-doped ZnO (GZO) thin films with different Ga concentrations were prepared by using the sol-gel spin-coating method. The surface morphologies and the growth orientations of the films were measured by using scanning electron microscopy and X-ray diffraction, respectively. The electrical properties were measured by using the Hall effect. The optical transmittances and reflectances of the films were measured as functions of the wavelength by UV-vis spectroscopy. The undoped ZnO thin films exhibited rough surfaces with particle-like structures. When Ga was incorporated, the particle sizes dramatically decreased without changes in the surface morphologies, and the c-axis growth orientations of the GZO thin films were significantly decreased. The optical transmittances clearly exhibited shifts in the band edge, and those in the visible range gradually increased with increasing Ga concentration. The absorption coefficients, refractive indices, extinction constants, dielectric constants, and optical conductivities of the films gradually decreased with increasing Ga concentration.

The Effect of Ga Content on the Recombination Behavior of Grain Boundaries in Cu(In,Ga)Se2 Solar Cells

ABSTRACTThe highest efficiency CuIn1-xGaxSe2 (CIGS) based solar cells have been produced from films with x∼0.3 which gives a value of Eg around 1.1-1.2eV. Increasing the Ga content of the CIGS absorber provides an increase in Voc, allows tuning of the band gap that can enhance performance under actual operating conditions, and potentially makes it possible to use CIGS films in multi-junction devices. However, champion cells have not yet been produced for values of x significantly greater than 0.3. This work focuses on how increased Ga content in CIGS films affects the recombination behavior of grain boundaries. Cathodoluminescence spectral imaging (CLSI) measurements on fully processed devices allow us to compare device properties with recombination behavior and optical properties of grain boundaries in films with different Ga content. Our data suggests that grain boundaries in high efficiency films with x∼0.3 exhibit a significant red shift in the CL spectra whereas grain boundaries in films with higher Ga content typically show either a small shift or none at all. This shift indicates band bending near the boundaries which could enhance charge separation and subsequent collection of carriers generated near grain boundaries. This is investigated statistically to identify trends in different regions of the films.

Growth behavior and electrical performance of Ga-doped ZnO nanorod/p-Si heterojunction diodes prepared using a hydrothermal method

The incorporation of foreign elements into ZnO nanostructures is of significant interest for tuning the structure and optical and electrical properties in nanoscale optoelectronic devices. In this study, Ga-doped 1-D ZnO nanorods were synthesized using a hydrothermal route, in which the doping content of Ga was varied from 0% to 10%. The pn heterojunction diodes based on the n-type Ga-doped ZnO nanorod/p-type Si substrates were constructed, and the effect of the Ga doping on the morphology, chemical bonding structure, and optical properties of the ZnO nanorods was systematically investigated as well as the diode performance. With increasing Ga content, the average diameter of the ZnO nanorods was increased, whereas the amount of oxygen vacancies was reduced. In addition, the Ga-doped ZnO nanorod/p-Si diodes showed a well-defined rectifying behavior in the I-V characteristics and an improvement in the electrical conductivity (diode performance) by the Ga doping, which was attributed to the increased charge carrier (electron) concentration and the reduced defect states in the nanorods by incorporating Ga. The results suggest that Ga doping is an effective way to tailor the morphology, optical, electronic, and electrical properties of ZnO nanorods for various applications such as field-effect transistors (FETs), light-emitting diodes (LEDs), and laser diodes (LDs).

Anisotropic Responsivity of AlGaN Metal–Semiconductor–Metal Photodetectors on Epitaxial Laterally Overgrown AlN/Sapphire Templates

Al0.4Ga0.6N metal–semiconductor–metal photodetectors on epitaxial laterally overgrown (ELO) AlN/sapphire templates show anisotropic device characteristics depending on the orientation of the electrode stripes with respect to the stripe pattern onto which the underlying ELO AlN buffer layers have been grown. With electrodes perpendicular to the stripes, a quantum efficiency (QE) of ∼140 was found for 20-V bias at room-temperature. This gain is explained by carrier transport along channels with increased Ga content resulting from faceted growth at the steps of the ELO template. The resulting potential barrier is confirmed by the activation energy found for the temperature dependence of the QE. In contrast, photodetectors with electrodes running parallel to these channels do not show gain but have an enhanced QE at elevated bias voltage compared to devices on planar AlN buffer layers. This effect is attributed to different densities of threading dislocations in the absorber layer.

Synthesis of single phase chalcopyrite CuIn1−xGaxSe2 (0 ≤ x ≤ 1) nanoparticles by one-pot method

Single phase chalcopyrite and near stoichiometric CuIn1−xGaxSe2 (0≤x≤1) nanoparticles were successfully synthesized by using a facile and rapid one-pot method. The effects of various Ga contents on crystal phase, morphology, element composition and absorption spectrum of the as-synthesized CuIn1−xGaxSe2 nanoparticles were investigated in detail. The XRD and Raman patterns indicated that the as-synthesized nanoparticles had a single phase chalcopyrite structure, and the diffraction peaks shifted toward larger diffraction angles or higher frequencies with increasing Ga content. The FE-SEM images showed that the as-synthesized nanoparticles were polydispersed in both size and shape, and the nanoparticles with higher Ga content were more prone to aggregate. The Vis–IR absorption spectra showed strong absorption in the entire visible light region. The estimated band gap increased from 1.00eV to 1.68eV as Ga content increasing.

Structure and Magnetic Properties of Ga Substituted Ni-Ferrites

Nanocrystalline Ga doped nickel ferrite [(NiFe2-xGaxO4 (x=0.0, 0.1, 0.3, 0.5 and 0.7)] powders have been synthesized by sol-gel auto-ignition method and the effect of non-magnetic gadillum content on the nanosize particles and magnetic properties has been studied. The X-ray diffraction (XRD) revealed that the powders obtained are single phase with spinel structure. The calculated grain size from XRD data have been verified using transmission electron microscopy (TEM). TEM photograph shows that the powders consist of nanometer sized grain. The size of nanoparticles decreases as the non magnetic Ga content increases. Magnetic hysteresis loops were measured at room temperature with maximum applied magnetic field of 20 KOe. As Ga content increases, the measured magnetic hysteresis curves became border and saturation magnetization (MS) increased up to x= 0.3 and further increase of x leads the magnetization to decrease. The results are explained according to the assumed cation distribution.

Crystallinity, etchability, electrical and mechanical properties of Ga doped amorphous indium tin oxide thin films deposited by direct current magnetron sputtering

Indium tin oxide (ITO) and Ga-doped ITO (ITO:Ga) films were deposited on glass and polyimide (PI) substrates by direct current (DC) magnetron sputtering using different ITO:Ga targets (doped-Ga: 0, 0.1 and 2.9wt.%). The films were deposited with a thickness of 50nm and then post-annealed at various temperatures (room temperature-250°C) in a vacuum chamber for 30min. The amorphous ITO:Ga (0.1wt.%Ga) films post-annealed at 220°C exhibited relatively low resistivity (4.622x10−4 Ωcm), indicating that the crystallinity of the ITO:Ga films decreased with increasing Ga content. In addition, the amorphous ITO:Ga films showed a better surface morphology, etchability and mechanical properties than the ITO films.

Opto-structural and electrical properties of chemically grown Ga doped MoBi2Se5 thin films

An arrested precipitation route was developed to obtain gallium doped MoBi2Se5 thin films on substrate support. High purity organometallic complexes of Mo–triethanolamine (Mo–TEA), Bi–triethanolamine (Bi–TEA), Ga–triethanolamine (Ga–TEA) allow to react with sodium selenosulphite (Na2SeSO3) in the presence of sodium dithionite (Na2S2O4) as a reducing agent in an aqueous alkaline reaction bath. As deposited thin films were characterized by X-ray diffraction, which reveals that material is nanocrystalline with mixed phases of rhombohedral (Bi2Se3)-hexagonal (MoSe2)-hexagonal (GaSe) structures. Scanning electron micrographs show the grain of granular morphology decreases with increase in Ga concentration. Energy dispersive x-ray analysis shows presence of Mo, Bi, Ga and Se elements in stoichiometric ratio confirms the chemical formula MoBiGaSe5. Optical absorbance of the films show direct allowed transition in visible region having band gap energy in the range of 1.30–1.47 eV. Thermoelectric power and electrical conductivity measurements have been carried out for thin film samples in the temperature range 300–500 K and results revealed that n-type semiconducting behavior. It is interesting to note that Ga doping in MoBi2Se5 changes n to p type conductivity.

Preparation and Characterization of Copper Gallium Diselenide Thin Films from the Solgel-Derived Precursors

A simple process for preparing CuGaSe2 (CGS) absorber layers was developed in this study. The solgel-derived Cu-Ga-O precursor paste with variable Ga3+/Cu2+ ratios was coated on glass substrates using a doctor-blade technique. The precursor films were selenided with a selenium vapor at the temperature ranging from 250 to 550°C. The GIXRD patterns showed that single-phase CuGaSe2 through the whole films was obtained at a Ga3+/Cu2+ molar ratio of 1.5 on selenization at 450°C. The Raman measurements also indicated that the grown CuGaSe2 thin films exhibited the chalcopyrite structure. The SEM images of the films reveal that with an increase in Ga/Cu ratio in the films, the amount of Cu2Se particles on the surface of the film was reduced. The resistivity of the films was increased with the increase in Ga content in the films. The formation mechanism of CuGaSe2 thin films was proposed based on the XRD and Raman measurements of the films. The binary copper selenides are formed first, and then these phases lead to the formation of CuGaSe2.

Ti–Ga binary alloys developed as potential dental materials

In this study, the microstructure, mechanical properties, castability, electrochemical behaviors and cytotoxicity of as-cast Ti–Ga alloys with pure Ti as control were systematically investigated to assess their potential application in dental field.The results of OM and XRD showed that the microstructure of all experimental as-cast Ti–Ga alloys exhibited single α-Ti phase at room temperature. Mechanical tests indicated that the tensile strength, Young's modulus, microhardness and wear resistance were improved monotonically with the increase of Ga content. The castability test showed that Ti–2Ga alloy increased the castability value of pure Ti by 14.2(±3.8)% (p<0.05). The electrochemical behaviors in both artificial saliva solutions indicated that the studied Ti–Ga alloys showed better corrosion resistance than pure Ti. The cytotoxicity test suggested that the studied Ti–Ga alloys produced no significant deleterious effect to L929 fibroblast cells and MG63 osteosarcoma cells, similar to pure Ti, indicating an excellent in vitro biocompatibility. The cell morphology test showed that both L929 and MG63 cells process excellent cell adhesion ability on all experimental materials. Considering all these results, Ti–2Ga alloy exhibits the optimal comprehensive performance and has potential for dental applications.

Cyclic voltammetry study of electrodeposition of CuGaSe2 thin films on ITO-glass substrates

The electrodeposition mechanism of CuGaSe2 (CGS) thin films on ITO substrates has been investigated using cyclic voltammetry technique. The cyclic voltammetric study was performed in unitary Cu, Ga and Se systems, binary Cu–Se, Ga–Se systems and ternary Cu–Ga–Se system. The electrodeposition metallic Ga from Ga unitary electrolytes is impossible due to its low reduction potential. No reduction peak was found for the reduction of Ga3+ to Ga in the cyclic voltammogram of unitary system. However, in the cyclic voltammogram of ternary Cu–Ga–Se system, reduction peak at −0.6 V was observed with addition of GaCl3. Also, current density of the peak was increased with increasing concentration of GaCl3. It is corresponded to the formation of gallium selenides and/or copper–gallium–selenium compounds. The contents of Ga in the films were significantly changed from −0.4 V to −0.6 V. SEM and XRD analysis also showed that surface morphology and crystalline phase of films were significantly changed with increasing Ga content.

Magnetostructural phase transition in Ga-doped MnNiGe compounds

The magnetic phase transitions in MnNiGe1 − xGax (x = 0.0725, 0.080, and 0.085) compounds were investigated by dc magnetization measurements. Due to the introduction of Ga, all the compounds crystallized in Ni2In-type structure at room temperature instead of TiNiSi-type structure for their parent compound MnNiGe. With increasing temperature, each compound goes through two magnetic phase transitions, i.e. magnetostructural phase transitions from antiferromagnetic (AFM) TiNiSi-type phase to ferromagnetic (FM) Ni2In-type phase and ferromagnetic to paramagnetic (FM–PM) transition of Ni2In-type phase. It was found that the magnetostructural phase transition temperatures Tt decreased with the increase of Ga content, while the FM–PM transition temperature TC almost did not change. Large inverse magnetic entropy ΔSM in the vicinity of Tt following a conventional one around TC was observed for each sample.

Magnetic properties and phase diagram of Ni50Mn50−xGax ferromagnetic shape memory alloys

We present the magnetic properties and the magnetic phase diagram of Ni50Mn50−xGax ferromagnetic shape memory alloys across a wide concentration range. Martensitic transformation, intermediate transformation, B2–L21 order–disorder transformation, Néel and Curie temperatures are determined for the prepared samples. The martensitic transformation temperature decreases with increasing Ga concentration and bends two times when crossing the Curie temperature and the intermediate-phase transformation temperature. Spontaneous magnetization and its composition dependence were also investigated. Composition dependence of the transformation temperatures and the spontaneous magnetization in the martensite phase of Ni50Mn50−xGax are compared with those of Ni50Mn50−xInx and Ni50Mn50−xSnx, revealing a similarity in the NiMn-based alloy systems.

Electronic and optical properties of strained InxGa1−xAs/GaAs and strain-free GaAs/Al0.3Ga0.7As quantum dots on (110) substrates

We investigate strained In${}_{x}$Ga${}_{1\ensuremath{-}x}$As/GaAs and strain-free GaAs/Al${}_{0.3}$Ga${}_{0.7}$As quantum dots (QDs) grown on (110)-oriented substrates by means of atomic empirical pseudopotentials and configuration interaction. We find that there is a significant piezoelectric effect on the exciton fine structure splitting (FSS) in strained QDs due to the in-plane character of the electric field. The ground-state bright excitons in these QDs are polarized along the [001] and [$\overline{1}$10] crystal directions, and have large FSSs. The linear degree of polarization is large and decreases linearly with an increase in Ga content, while it is nearly zero and independent of Ga content in In${}_{x}$Ga${}_{1\ensuremath{-}x}$As/GaAs QDs with similar shape and size grown on (001) substrates.

Controllability of Structural, Optical and Electrical Properties of Ga doped ZnO Nanowires Synthesized by Physical Vapor Deposition

The control of Ga doping in ZnO nanowires (NWs) by physical vapor deposition has been implemented and characterized. Various Ga-doped ZnO NWs were grown using the vapor-liquid-solid (VLS) method, with Au catalyst on c-plane sapphire substrate by hot-walled pulsed laser deposition (HW-PLD), one of the physical vapor deposition methods. The structural, optical and electrical properties of Ga-doped ZnO NWs have been systematically analyzed, by changing Ga concentration in ZnO NWs. We observed stacking faults and different crystalline directions caused by increasing Ga concentration in ZnO NWs, using SEM and HR-TEM. A <TEX>$D^0X$</TEX> peak in the PL spectra of Ga doped ZnO NWs that is sharper than that of pure ZnO NWs has been clearly observed, which indicated the substitution of Ga for Zn. The electrical properties of controlled Ga-doped ZnO NWs have been measured, and show that the conductance of ZnO NWs increased up to 3 wt% Ga doping. However, the conductance of 5 wt% Ga doped ZnO NWs decreased, because the mean free path was decreased, according to the increase of carrier concentration. This control of the structural, optical and electrical properties of ZnO NWs by doping, could provide the possibility of the fabrication of various nanowire based electronic devices, such as nano-FETs, nano-inverters, nano-logic circuits and customized nano-sensors.