MLEK crystal growth of (100) indium phosphide

We have used a combined magnetic liquid encapsulated Kyropoulos/Czochralski (MLEK/ MLEC) technique to produce twin-free indium phosphide (InP) crystals. This technique has advantages over the standard LEC method used for commercial production of InP. By stabilizing convective flows with a magnetic field and controlling the angle between solid and liquid, one can grow large diameter twin-free (100) InP crystals; they are shaped with a flat top as is typical for Kyropoulos growth, and then pulled from the magnetically stabilized melt as in Czochralski growth. This shaping method has the benefit of maximizing the number of single crystal wafers which can be sliced from the boule. MLEK InP growth is distinguished from other methods such as LEC and MLEC with respect to solid-liquid interface shape, dislocation density, and impurity distribution. This process has demonstrated that twin-free InP (100) crystals can be consistently grown.     

Zone melting of indium phosphide

Bulk indium phosphide crystals have been prepared by zone melting with dislocation densities 104 ≤ N_d ≤ 105 cm^-2. The residual impurity level in nominally undoped crystals and the dopant distribution in Cd-, Sn- and Ge-doped zone melted ingots, as revealed by spark source mass spectrometric analyses, indicate a strong interaction between segregation at the solid/liquid interface and vapor transport. The effective distribution coefficients for Sn and Ge in zone melted InP are k_e(Sn) = 0.3 and k_e(Ge) = 0.4. The free electron concentration measured in the middle section of nominally undoped ingots is N_D-N_A = 1.9 × 10¹⁵ cm^-3 corresponding to a Hall mobility Μ_e = 3263 cm^2V-1sec^-l.     

Hydrogen sulfide plasma passivation of indium phosphide

The electrical properties of the SiO₂-InP interface are improved using in-situ H₂S plasma pretreatments as a reliable method of sulfidizing the InP surface prior to film deposition. High frequency (1 MHz) and quasi-static capitance-voltage measurements on metal-insulator-semiconductor structures show reduced interface trap densities. X-ray photoemission spectroscopy analysis indicates that prior to film deposition, sulfur is bonded to phosphorus at the surface; but after film deposition, very little sulfur remains. Spectroscopic ellipsometry measurements confirm that the interface does remain modified even after film deposition, and photoluminescence data show increased signal intensity for thin SiO₂ film on InP with H₂S pretreatments as compared to untreated samples.     

Influence of iron content on electrical characteristics and thermal stability of LEC indium phosphide

The Hall mobilities (conductivity type) measured on many Fe-doped InP wafers have been used as a parameter for material assessment. The samples can essentially be assigned to three groups. Interpretation of the experimental data is given for each group of samples. Furthermore, we report the results of electrical measurements on annealed InP and show the kind of correlation existing between the electrical characteristics of as-grown and annealed InP. Finally, we report a study on the homogeneity of Fe-doped InP on a macroscale. It is seen that the experimental resistivity profiles along the wafer diameters are a function both of the Fe and shallow inpurities profiles.     

Structural,optical and photocatalytic properties of MgO/ZnO nanocomposites prepared by a hydrothermal method

MgO/ZnO nanocomposites were synthesized by a hydrothermal method at 180 °C for 15 h. The XRD results showed that MgO phase occurred over the whole range of Mg concentration used. The MgO induced a growth of crystallite size of ZnO. The particle shape of ZnO altered from an agglomerated nanosheet to a hexagonal platelet when loading with MgO and MgO was shaped in small rod structures. The optical band gap was increased from 3.190 to 3.225 eV. The photocatalytic degradation depended upon the irradiation time and MgO loading contents. In this study, the 5 mol% MgO/ZnO nanocomposite exhibited the best photocatalytic degradation of 98.3% during irradiation by blacklight for 90 min.     

Phosphorus-overpressure rapid thermal annealing of indium phosphide

A rapid thermal annealing technique for InP is described in which a controllable phosphorus overpressure, generated by heating red phosphorus, suppresses the dissociation of InP at required annealing temperatures. Two annealing configurations were used to independently study the effects of phosphorus overpressures, anneal temperatures and gas flow rates on the post-anneal electrical and morphological properties of low dose Si-implanted InP:Fe. The advantage of phosphorus overpressure annealing over close-contact annealing is shown, and comparison is made with Si₃N₄ encapsulated annealing. Gas flow velocities close to the sample are found to significantly affect the surface morphology, and a static layer immediately above the sample is found to be beneficial.     

Improvement of visible light photocatalytic activity over graphene oxide/CuInS2/ZnO nanocomposite synthesized by hydrothermal method

In this study, graphene oxide/CuInS₂/ZnO as a new photocatalyst with light absorption properties in the visible region were successfully synthesized via hydrothermal route. The UV–vis absorption spectra of the catalyst suggested that the graphene oxide/CuInS₂/ZnO is active under visible light. It was evaluated the photocatalytic activities of graphene oxide/CuInS₂/ZnO on the degradation of Rhodamine B under visible light irradiation and was found that the graphene oxide/CuInS₂/ZnO obtained exhibit photocatalytic activity higher than single ZnO and CuInS₂/ZnO. Presence of graphene oxide with high specific surface area and great conductivity make it as a good support for CuInS₂/ZnO and improves removal efficiency for degradation of Rhodamine B.     

非晶InP薄膜的光学性质与退火效应

本文研究由射频溅射法制备的非晶InP薄膜的光学性质及其退火效应.薄膜光学性质由椭圆偏振光谱法测量.退火是在300、350、400、420℃的温度下于密闭容器中进行.结果表明,经400℃退火后,薄膜光学性质发生明显改变,反映薄膜已由非晶态转变为多晶态.指出用光学性质的改变来描述晶化过程可能更加灵敏.     

InP growth and properties

Bulk polycrystalline InP is synthesized from the elements via a gradient freeze process. Hall data for a typical boule are N_d-N_a= 4.7 × 10¹⁵/cm³ and Μ77 = 28,000 cm²/V-sec. Photoluminescence data indicate that zinc is present as an acceptor impurity in the polycrystalline InP and in nominally undoped LEC single crystals grown using the synthesized InP as charge material. A series of doping experiments have determined the effective segregation coefficient to be 1.6 × 10⁻³ for Fe in InP. Semi-insulating InP crystals with resistivity > 10⁷ ohm—cm have been grown consistently from melts doped with 150 ppm Fe.     

In-situ synthesis and growth of indium phosphide

The high partial pressure of phosphorus at the stoichiometric melting point of InP precludes the in-situ synthesis in the puller by simple admixture of indium and phosphorus. This paper describes a system that was considered for the in-situ synthesis and growth of InP single crystal, utilizing the phosphorus vapor injection method. The advantages of this two-heater side-by-side injection synthesis system is dis-cussed and the effect of chamber pressure and phosphorus temperature on the InP synthesis yield is described. The procedures used for in-situ synthesis and growth are also described. Electrical and optical properties of LEC cry-stals grown by in-situ synthesis compare favorably with those of crystals grown from polycrystalline charges synthe-sized with the high-pressure autoclave or the gradient freeze method. This work was partially supported by ARO Contract DAAG29-79-C-0009, and was presented first at the 24th Annual Elec-tronic Materials Conference held at Fort Collins, Colorado, June 1982.     

Structural,optical and photocatalytic properties of ZnO nanoparticles modified with Cu

ZnO and ZnO modified with Cu nanoparticles have been prepared by a simple forced hydrolysis method. The concentration of Cu incorporated in ZnO ranged from 1% to 5% by atomic weight, and the influence of Cu concentration on the physical properties of ZnO and the relation to the photocatalytic performance has been investigated. The prepared ZnO and ZnO:Cu samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and UV–vis transmittance spectroscopy. The results show that the ZnO nanomaterial was crystalline with the hexagonal wurtzite structure, with the preferential orientation of the grains along the (101) plane. The average grain size for samples with 1–5% Cu was in the range of 11–29 nm. The ZnO nanoparticles annealed at 420 °C showed an increased photocatalytic activity for the decomposition of methylene blue.     

The effect of hydrostatic pressure on the electronic and optical properties of InP

Based on the empirical pseudo-potential method, the electronic and optical properties of the InP compound in the zinc-blende structure at ambient and under hydrostatic pressure are reported. The first-order pressure coefficients of the main band gaps (at Γ, X, and L) are given. The agreement between our calculated hydrostatic deformation potential and the available experimental data is better than 5%, whereas for the crossover pressure from direct to indirect band gap is about 10% less. The valence bandwidth increases with increasing pressure reflecting the decreased ionicity in the material of interest. Besides the electronic properties, the effect of pressure on the dielectric function is also analysed.     

Preparation and optical and photocatalytic properties of Ce-doped ZnO microstructures by simple solution method

We prepared ZnO photocatalysts with different Ce-doping levels using a simple one-step solution method utilizing Zn(NO₃)₂, Ce(NO₃)₃, and NaOH as raw materials. X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area analysis, ultraviolet–visible diffusion spectroscopy, and photoluminescence spectroscopy were used to characterize the products. Ce-doping greatly influences the size, morphology, and optical properties of the samples. The particle size of Ce/ZnO samples decreases and the specific surface area increases accordingly compared with that of pure ZnO. The optical absorption edge of the Ce/ZnO samples displays an obvious red shift. Moreover, the band gap energy decreases with the increasing Ce content. The Ce/ZnO samples exhibit significantly enhanced photocatalytic performance than pure ZnO. The 1% Ce/ZnO sample possesses excellent photocatalytic activity in decomposing methylene blue (MB). The MB degradation efficiency reaches 96.11% after 140 min of irradiation.     

Facile synthesis and photocatalytic activity of hollow micro-spherical zinc sulfide caps

Novel zinc sulfide (ZnS) hollow micro-spherical caps were produced via a facile thermal evaporation of ZnS and Zn powders without any types of templates. The samples are characterized by X-ray diffraction, scanning electron microscopy, Raman spectra and fluorescence spectra. The results demonstrate that the synthesized ZnS nanoparticles are hollow micro-spherical caps with the diameters ranging from 4 to 8 μm and a relatively homogeneous shell thickness of about 40 nm. Furthermore, the formation mechanism of ZnS hollow micro-spherical caps was also suggested. Moreover, the photocatalysis test shows that the ZnS hollow micro-spherical caps exhibit a high photocatalytic activity, thereby implying that the surface of ZnS can promote the separation of photogenerated electron–hole pairs and enhance the photocatalytic activity.     

Hydrothermal synthesis of Ga-doped In2O3 nanostructure and its structural,optical and photocatalytic properties

In this work, pure and Ga-doped In₂O₃ nanostructures have been synthesized by facile template-free hydrothermal method. The structural, morphological and optical properties are characterized by using XRD, FT-IR, HR-SEM and TEM, EDS, XPS, UV-DRS, and PL techniques. X-ray diffraction analysis indicates a pure cubic phase while crystallite size decreases with Ga doping. HR-SEM and TEM observations reveal irregular-shaped and spindle-like nanostructures with enhanced crystallinity and reduction in particle size with Ga doping. XPS spectra reveal the oxidation state of Ga is +3. The energy band gap estimated by UV–vis DRS spectroscopy is found to increase slightly from 3.40 to 3.45 eV with Ga doping. Photoluminescence spectra display violet, blue and green emission peaks are observed during Ga doping concentrations. Photodegradation of Methylene blue dye under ultra violet light radiation is found to double with Ga doping; i.e. 48% for Ga- In₂O₃ compared to 22% for pure In₂O₃.     

Microwave hydrothermal synthesis of BiFeO3: Impact of different surfactants on the morphology and photocatalytic properties

Pure-phase BiFeO₃ catalysts with different morphologies were synthesized by microwave hydrothermal treatment at 200 °C with and without surfactant. The as-prepared catalysts were characterized by X-ray diffraction, scanning electron microscopy, and diffuse reflectance spectroscopy. Their photocatalytic properties were also explored. Ball-like (no surfactant), flower-like (EDTA), and honeycomb-like (polyvinylpyrrolidone) BiFeO₃ catalysts were obtained. Surfactant addition decreased the bandgap of BiFeO₃ catalysts. The specific surface area for ball-like, flower-like, and honeycomb-like BiFeO₃ catalysts was 7.48, 3.48, and 12.38 m²/g, and the rate of rhodamine B degradation under UV light was 49%, 61%, and 87%, respectively, at 4 h.     

Structural and optical properties of functionalized multi-walled carbon nanotubes

Herein, we report the functionalization of multiwalled carbon nanotubes (MWCNTs) using meta-Chloroperoxybenzoic acid (mCPBA) as an oxidizing agent. Epoxy groups are incorporated into the sidewall of MWCNTs and the prepared functionalized multiwalled carbon nanotubes (F-MWCNTs) were characterized using FT-IR spectroscopy, X-ray diffraction, Raman spectroscopy and UV–visible spectroscopy. Morphology of MWCNTs and F-MWCNTs was determined using Scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM results clearly indicated that the diameter of F-MWCNTs is increased by 120% as compared to neat MWCNTs. From UV–visible spectroscopy data, band gap of F-MWCNTs was calculated using Tauc equation and it was found to be 3.9 eV. Photo emission property of F-MWCNTs was analyzed using photoluminescence spectroscopy. F-MWCNTs showed nice emission in the visible region and it depended upon the excited wavelength. These functionalized carbon nanotubes could find use as tunable optoelectronic devices in future nanotechnology.     

Visible light photocatalytic performance of hierarchical BiOBr microspheres synthesized via a reactable ionic liquid

Hierarchical BiOBr microspheres were synthesized via a one-pot solvothermal process in the presence of ethylene glycol and 1-butyl-3-methylimidazolium bromide ([BMIM]Br) as a reactable ionic liquid. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance absorption spectra, nitrogen adsorption–desorption measurements, and photoluminescence spectroscopy. The photocatalytic activity of BiOBr microspheres was evaluated in terms of the degradation of Rhodamine B (RhB), methyl orange (MO), and 4-chlorophenol (4-CP) under visible light irradiation. We found that the solvothermal temperature had important effects on the crystallinity, crystallite size, optical property, adsorptive performance, and photocatalytic activity of BiOBr microspheres. BiOBr microspheres with a specific surface area of 15.7 m² g⁻¹ prepared at 160 °C exhibited the best adsorption and photocatalytic performance for RhB degradation in aqueous solution. However, this sample showed hardly any activity for photodegradation of 4-CP. Tests using radical scavengers confirmed that h⁺ and O₂⁻ were the main reactive species during RhB degradation. A possible mechanism for photocatalysis by BiOBr microspheres is proposed.     

Optical and electrical properties of CdGeAs2

Large-grained ingots of CdGeAs₂ have been grown from near-stoichiometric melts. Resistivity and Hall coefficient (R_H) measurements were made on a large number of samples at 77 and 300 K and in some cases up to 450 K. Good fits to the log R_H vs 1/T plots are obtained by using a model that assumes three kinds of electronic levels within the energy gap: donors, shallow acceptors, and acceptors with an ionization energy of 0. 30 eV. The deep acceptors are probably native defects, since their concentration varies by nearly four orders of magnitude from ingot to ingot with little change in impurity concentration. Between the intrinsic absorption edge at about 2. 5 Μm and the two-phonon absorption band at 18 Μm, the optical absorption increases with increasing deep acceptor concentration. By using oriented single-crystal samples ∼ 1 cm on a side, conversion efficiencies as high as 27% have been achieved for second-harmonic generation with single-mode pulses from a CO₂ TEA laser.     

Controlled oxygen incorporation in indium gallium arsenide and indium phosphide grown by metalorganic vapor phase epitaxy

The defect engineering in metalorganic vapor phase epitaxy In_xGa_1-xAs and InP by controlled oxygen doping using diethyl aluminum ethoxide (DEALO) was developed in this study. DEALO doping has led to the incorporation of Al and O, and the compensation of shallow Si donors in In_xGa_1−xAs: Si with 0 ≤ x ≤ 0.25. With the same DEALO mole fraction during growth, the incorporation of Al and O was found to be independent of x, but the compensation of Si donors decreases with increasing In content. Deep level transient spectroscopy analysis on a series of In_xGa_1-xAs: Si. samples with 0 ≤ x ≤ 0.18 revealed that oxygen incorporation led to a set of deep levels, similar to those found in DEALO doped GaAs. As the In composition was increased, one or more of these deep levels became resonant with the conduction band and led to a high electron concentration in oxygen doped In_0.53Ga_0.47As. Low temperature photoluminescence emission measurements at 12K on the same set of samples revealed the quenching of the near-band edge peak, and the appearance of new oxygen-induced emission features. DEALO doping in InP has also led to the incorporation of Al and O, and the compensation of Si donors due to oxygen-induced multiple deep levels.