Small Indium Research Articles

Theoretical DFT study of the structure and chemical activity of small indium(III) oxide clusters

The B3LYP/Lanl2dz and B3LYP/SDD levels of DFT have been used to describe the structural properties of small stoichiometric indium(III) oxide clusters. It was shown that the most stable structures for the monomer and dimer are linear and cubic, respectively, in origin. The most stable trimer is due to the formation of three eight-membered and two six-membered rings with alternation of In and O atoms. Among neutral and monocation tetrameric structures, formation of an “arrowhead” isomer is energetically less favorable than the global minimum structure that has eight six-membered and six four-membered rings. In the pentamer and octamer, a few centers of higher coordination number and a variety of In–O bond lengths are observed. The other centers cannot be fitted to the characteristic bixbyite structure, however, so the larger octamer cannot be a good model for mimicking the properties of the In2O3 crystal structure. An H-terminated cluster model consisting of In13O27H15 is proposed that well describes basic features of indium oxide and tin-doped indium oxide (ITO) structures.

Electric field effects on optical properties in zinc-blende InGaN/GaN quantum dot

The effect of electric field on exciton states and optical properties in zinc-blende (ZB) InGaN/GaN quantum dot (QD) are investigated theoretically in the framework of effective-mass envelop function theory. Numerical results show that the electric field leads to a remarkable reduction of the ground-state exciton binding energy, interband transition energy, oscillator strength and linear optical susceptibility in InGaN/GaN QD. It is also found that the electric field effects on exciton states and optical properties are much more obvious in QD with large size. Moreover, the ground-state exciton binding energy and oscillator strength are more sensitive to the variation of indium composition in InGaN/GaN QD with small indium composition. Some numerical results are in agreement with the experimental measurements.

Optical properties of CuAlS2 with small indium content

AbstractBulky CuAlS2 single crystals were grown by traveling‐heater method (THM) using indium solvent, and shown to have small indium content and represent solid solutions CuAl1–xInxS2 of CuAlS2‐CuInS2 system The composition with x = 0.24 has been studied by spectroscopic ellipsometry at room temperature. The principal components of dielectric function, ϵ⊥ (E⊥C) and ϵ∥ (E∥C), have been obtained in the spectral range 0.75‐6.0 eV. The critical point analysis has been performed and the optical transitions responsible for the observed critical points have been assigned by taking account of the available electronic band structures of CuAlS2 and CuInS2. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electroluminescence from Nanocrystals in an Electromigrated Gap Composed of Two Different Metals

We present a technique for making nanoscale gaps with work function offsets based on electromigrating leads composed of two different metals. Electroluminescence spectra from plain metal gaps with and without CdSe/ZnS (core/shell) nanocrystals are qualitatively very similar and exhibit features that are much broader than the photoluminescence spectra obtained from the same nanocrystals. These observations can be explained by inelastic scattering of conduction electrons in the metal leads or by electroluminescence from small metallic clusters that can form during the fabrication process. However, electroluminescence that spectrally coincides with nanocrystal photoluminescence can be observed in devices containing nanocrystals formed by electromigrating Pt leads bridged with small indium islands. This suggests that electromigrating leads made of different metals is a promising route to fabricating nanoscale gaps with work function offsets for optoelectronic devices.

Phase composition of electrodeposited silver-indium alloys

The phase composition of electrochemically obtained Ag-In alloy coatings electrodeposited at different conditions was determined. With the increase in the current density, both indium content and heterogeneity of the deposited layers increase. The amount of the indium-richer phase increase as well. Before the thermal treatment, the phases Ag, Ag3In, and In4Ag9 are observed in coatings with spatio-temporal structures. As a result of heating the new phase Ag4In appears at temperatures above 500 °C and indium is oxidized up to In2O3 from the oxygen in the heating chamber. Up to 500 °C, the spatio-temporal structures are still visible. Probably they consist of both Ag-rich α-phase and one of the phases of the alloy system with small indium content, such as Ag4In or Ag3In.

Assembly of ordered carbon shells on GaN nanowires

In situ annealing experiments on individual group III-nitride nanowires (NWs) in a transmission electron microscope demonstrate the encapsulation of GaN wires in crystalline carbon shells in the presence of C at moderate temperatures. The complete encapsulation of GaN wires in carbon shells can be achieved when small indium metal clusters are introduced on the wire surface. No encapsulation is observed on pure GaN wires under the same conditions. The observations suggest a general processing route for the formation of semiconductor core/C-shell NW structures based on surface decoration with small metal clusters.

Carrier loss and luminescence degradation in green-light-emitting InGaN quantum wells with micron-scale indium clusters

Influence of the size of indium clusters on optical properties of green-light-emitting InGaN quantum wells (QWs) was investigated by photoluminescence (PL), cathodoluminescence, PL excitation, and time-resolved PL techniques. Low luminescence efficiency was observed for green-light-emitting InGaN QWs with micron-sized indium clusters, in contrast to the case of InGaN QWs with submicron-sized small indium segregation. Both the thermal activation energy and the carrier lifetime dramatically decreased, while a large Stokes-like shift between absorption edge and PL peak energy was still observed for the InGaN QWs with micron-sized indium clusters. These facts indicate that the effective potential barrier between radiative and nonradiative channels (thus effective carrier localization) rapidly decreases due to the formation of micron-sized large indium clusters possessing a number of nonradiative centers, leading to significant luminescence degradation.

Ionization potentials and structures of small indium monoxide clusters

We report a combined experimental and theoretical study of the structures and ionization potentials of small InNO clusters (N=1–8). The clusters are produced using a laser vaporization cluster source, laser ionized, and mass selectively recorded by a time-of-flight mass spectrometer. Threshold photoionization spectroscopy was performed using photon energies of 4.59–5.96 eV and 6.43 eV. Adiabatic and vertical ionization potentials were compiled from the photoionization efficiency curves. Remarkably low values were obtained for In3O and In7O. Geometric and electronic structures of the InNO and InNO+ clusters were computed with density functional theory using the hybrid B3LYP functional. The bonding in these clusters is analyzed by means of Bader’s atoms in molecules method. Calculated adiabatic and vertical ionization potentials are in good agreement with the experimental values.

Characterizations of GaN films grown with indium surfactant by RF-plasma assisted molecular beam epitaxy

A small indium flux was used as a surfactant during the growth of gallium nitride by rf-plasma assisted molecular beam epitaxy. The effects of the In surfactant on the optical and structural properties of undoped GaN were studied by photoluminescence (PL), X-ray diffraction, atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS). PL studies show that the use of In surfactant is beneficial to the reduction of deep-level defects. The X-ray rocking curves demonstrate a 20% decrease in the full width at half maximum value for the films grown with In surfactant. AFM studies show that the root mean squared surface roughness for films grown with and without In surfactant are 5.86 and 6.99 nm respectively indicating significant improvement in surface morphology. The improved surface morphology is attributed to the enhanced 2-dimensional growth promoted by the application of In surfactant. RBS studies show that the χ min values along [0 0 0 1] direction are 2.06% and 2.16% for the samples grown with and without In surfactant respectively. Off-normal ion channeling studies were performed to further investigate the effects of In surfactant on the crystallinity. It is found that the number density of stacking faults is smaller for the sample grown with In surfactant compared to the one grown without In surfactant. However, defect analysis shows that dislocations are found in the sample grown with In surfactant in contrary to the one grown without In surfactant. We speculate that there is a thickness limit of GaN grown with In surfactant and the thickness of our samples exceed this limit, leading to the presence of dislocation.

Current Density-Voltage and Capacitance-Voltage Characteristics of Local p-n Junction Structures in CuInSe2 Single Crystals

Local p-n junction were obtained under room temperature conditions in CuInSe2 by applying strong electric field through small indium and copper contacts. The current density voltage (J-V) and the capacitance-voltage (C-V) of three different samples were measured at room temperature. The J-V method shows that the current is dominated by the drift component of the injected carriers. The C-V method gave a barrier height of 1.04 eV for all three samples which agrees with the reported energy gap of this material. Analysis of these results indicate that the p-n junction structures formed by strong electric fields are hihgly compensated and the current transport is dominated by the space charge limited current effect.

The Effect of Indium Surfactant on the Optoelectronic and Structural Properties of MBE Grown Gallium Nitride

ABSTRACTGallium nitride films were grown by rf-plasma assisted molecular beam epitaxy. A small indium flux was used as surfactant during the growth. The optical and electrical properties of the films grown with and without In surfactant were characterized by investigating the photoluminescence (PL), high resolution x-ray diffraction (HRXRD) and low-frequency noise power spectra. The sample grown in the presence of In surfactant showed a suppressed yellow luminescence (YL) compared to the one grown without In surfactant. Significant reduction in the full width at half maximum of the GaN (0002) x-ray diffraction peak, indicating a better film quality, was obtained when In surfactant was used during growth. Atomic force microscopy studies show that the root mean squared surface roughness for films grown with and without the In surfactant are 5.86 and 6.99 nm respectively indicating significant improvement in surface morphology. This is attributed to the enhanced 2-dimensional growth by In surfactant. A smaller Hooge parameter was obtained from the low-frequency noise measurement for the sample grown with In surfactant indicating that application of In surfactant led to significant reduction in the trap density of the material.

Modelling of solution growth of silicon from small indium droplets – homogeneous nucleation

The nucleation frequency and the size of the critical nucleus of silicon in an indium solution have been described on the basis of the classical theory. Due to a lack of reliable data for the free interface energy of crystalline silicon and liquid indium a simple approximation using the Young's equation and the Eötvös's rule has been applied. The results of the calculation have been compared with experimental data of melt solidification both of the chemically similar Ge and of a substance with a low melting point. In spite of the remaining uncertainties, the homogeneous nucleation of semiconductors in metallic solutions requires considerable undercooling. The high values of the interface energy are mainly responsible for this behaviour. From the calculated dependence of the size of the critical nucleus on the undercooling one can expect that micro-crystallites are stable in a slightly undercooled solution.

Nucleation of the Supercooled Normal to Superconducting Phase Transition in Small Indium Spheres Induced byγRadiation

We have observed that low energy $\ensuremath{\gamma}$ rays nucleate the supercooled normal to superconducting phase transition in micron-sized indium spheres. The mechanism for the nucleation in the superconducting sphere may have similarities to some aspects of the ``baked Alaska'' model proposed by Leggett for liquid ${}^{3}$He in which cosmic rays nucleate the transition from the supercooled superfluid $A$ phase to the $B$ phase.

Metalorganic Vapor Phase Epitaxy of Thick InGaN on Sapphire Substrate

Growth of thick InGaN films was performed on single crystal films of GaN or AlGaN and buffer layers of AlN, GaN or AlGaN by metalorganic vapor phase epitaxy (MOVPE). In the growth of InGaN on GaN or AlGaN films, smooth InGaN films with small indium mole fractions were grown in the initial growth stage caused by strong stress due to lattice mismatch. However, with an increase in thickness of the InGaN film surface became rough due to the generation of InGaN grains with large indium mole fractions. Smooth and thick (∼2 µ m) InGaN films with large indium mole fractions were grown on AlN, GaN or AlGaN buffer layers.

Improved substrate temperature stability during molecular beam epitaxy growth using indium free mounting of small substrates of various shapes

Large substrate surface temperature decreases are observed during molecular beam epitaxy growth onto small indium bonded substrates, due to coating of the molybdenum block. These large temperature transients, along with other difficulties associated with indium bonding (e.g., potential substrate surface damage, unwanted indium on the back of the substrate) make indium free substrate mounting desirable, however, indium free mounting systems have previously been restricted to whole standard‐sized round wafers. In this study we compare the temperature characteristics of new indium free modular substrate mounting blocks, which can accommodate substrates of various sizes (up to 3 inch diameter) and shapes, with traditional indium mounting of small substrates. Although the new modular indium free holders have a large molybdenum surface area exposed to the molecular beams, we find that the substrate surface temperature transients during growth are reduced to nearly negligible levels versus similar growth on indium bonded substrates, due to the effective thermal isolation of the substrate from the molybdenum. The real effects of these temperature differences observed by in situ pyrometry were confirmed by ex situ deep level transient spectroscopy (DLTS) measurements of homoepitaxial GaAs films, which show a two‐to‐three order of magnitude trap density increase in films grown on indium bonded substrates versus films grown on substrates mounted without indium bonding. This DLTS result is consistent with a real growth temperature difference between the two mounting techniques as was measured in situ by pyrometry.

Melting and solidification of small indium particles embedded in an aluminum matrix

Rutherford backscattering analysis in combination with channeling has been used to study melting and solidification temperature cycles of nanometer-sized indium particles in aluminum. The indium particles were formed by implantation of 100–250 keV In + atoms into (110) aluminum single crystals using fluences between 1.7 × 10 20 m −2 and 1.5 × 10 21 m −2. It was found that the smaller embedded indium particles in sample A (radius 4 nm on average) exhibit higher melting temperature than the larger inclusions of sample B (radius 40 nm on average). The solidification of the indium inclusions in sample A also shows larger undercooling than those of sample B. The superheating of the inclusions of sample A was found to be 23 K and the undercooling was 21 K. These results are in qualitative agreement with earlier TEM results and with simple thermodynamic considerations. By the use of channeling, it was found that a crystal axis of the inclusions with a characteristic half-width at half maximum value, equal to the fcc indium 〈110〉 axis, was in perfect alignment with the 〈110〉 direction of the aluminum matrix. This indicates a topotactical orientation between the indium inclusions and the aluminum matrix. It was expected that the normalized minimum yield obtained from channeling in the indium inclusions would decrease with increasing inclusion size, but the opposite was observed. This may indicate an increasing elastic strain in the inclusions with increasing particle size.

Evidence of point defect supersaturation during Zn diffusion in InP single crystals

Formation of defects during Zn diffusion into undoped and semi-insulating Fe-doped InP single crystals at 700 °C was observed by transmission electron microscopy for various diffusion conditions. Agglomerates of predominantly perfect interstitial-type dislocation loops, dislocations, and small indium precipitates inside voids are observed in the Zn-diffused crystal region. In addition, large planar arrays of precipitates are formed by climbing dislocations. From these observations it is concluded that the incorporation of Zn on In sublattice sites creates a supersaturation of In self-interstitials which is relieved by dislocation loop formation leading to a supersaturation of P vacancies and void formation.

Anion photoelectron spectroscopy of small indium phosphide clusters (InxP−y; x,y=1–4)

Small indium phosphide clusters having 2–8 atoms are studied using anion photoelectron spectroscopy of InxP−y (x,y=1–4). From these spectra, the electron affinities are determined. Both ground and low-lying excited electronic states of the neutral clusters are observed. An electronic gap is shown in the even cluster anion spectra.

Properties of InGaAs epitaxial layers lattice matched to InGaAs single crystal substrates

The structural and optical properties of In x Ga 1 − x As (0 < x < 0.09) epitaxial layers grown by low pressure metalorganic vapour phase epitaxy (MOVPE) on lattice matched single crystal ternary alloy substrates with the same composition have been studied. They are compared with layers grown simultaneously on GaAs (lattice mismatch up to 0.06%) and on ternary substrates. The lattice matched layers are characterized by a narrow photoluminescence and X-ray linewidth which reflects their excellent structural quality. As the indium concentration increases, the improvement of these properties over those of mismatched layers and of the substrates themselves emphasizes the importance of lattice matched epitaxial buffer layers for the control of strain and defect density in strained structure devices even at relatively small indium concentration.

Small lead and indium inclusions growing topotactically in aluminium

Small lead and indium inclusions growing topotactically in aluminium