Current conduction mechanisms of RF-Magnetron sputtered Y2O3 gate oxide on gallium nitride

Current conduction mechanisms through as-deposited and post-deposition annealed (200–800 °C) RF-magnetron sputtered Y₂O₃ gate oxides on n-type GaN have been systematically investigated with current–voltage measurements at temperature in the range of 25–175 °C. The possible current conduction mechanisms that govern the leakage current of Y₂O₃/GaN metal-oxide-semiconductor test structure are space-charge-limited conduction, Schottky emission, Poole–Frenkel emission, and Fowler-Nordheim tunneling. The dominance of these conduction mechanisms is depending on applied electric field and measurement temperatures.     

Synthesis, structure and thermal analysis of the gallium complex of 1,4,7,10-tetraazacyclo-dodecane-N,N′,N″,N-tetraacetic acid (DOTA)

As part of our efforts to synthesize gallium bioconjugates based on folic acid and thiamin we have utilized 1,4,7,10-tetraazacyclo-dodecane-N,N′,N″,N-tetraacetic acid (DOTA) as the chelating ligand for gallium(III). The reaction of gallium chloride with DOTA at room temperature in aqueous solution affords the complex [Ga(HDOTA) · 5.5H₂O] (1), which is characterized by single-crystal X-ray spectroscopy, electrospray mass spectrometry and thermal gravimetric analysis. Gallium displays 6-coordinate distorted octahedral geometry within a puckered macrocyclic DOTA framework. The equatorial plane comprises two nitrogens of the DOTA ring and two oxygens from two of the four pendant carboxylic acid groups. The axial positions are comprised of the remaining two transannular nitrogens of the DOTA ring.     

Synthesis and structure of In(IO3)3 and vibrational spectroscopy of M(IO3)3 (M=Al, Ga, In)

The reaction of Al, Ga, or In metals and H₅IO₆ in aqueous media at 180 °C leads to the formation of Al(IO₃)₃, Ga(IO₃)_3, or In(IO₃)₃, respectively. Single-crystal X-ray diffraction experiments have shown In(IO₃)₃ contains the Te₄O₉-type structure, while both Al(IO₃)₃ and Ga(IO₃)₃ are known to exhibit the polar Fe(IO₃)₃-type structure. Crystallographic data for In(IO₃)₃, trigonal, space group , a=9.7482(4) Å, c=14.1374(6) Å, V=1163.45(8) Z=6, R(F)=1.38% for 41 parameters with 644 reflections with I>2σ(I). All three iodate structures contain group 13 metal cations in a distorted octahedral coordination environment. M(IO₃)₃ (M=Al, Ga) contain a three-dimensional network formed by the bridging of Al³⁺ or Ga³⁺ cations by iodate anions. With In(IO₃)₃, iodate anions bridge In³⁺ cations in two-dimensional layers. Both materials contain distorted octahedral holes in their structures formed by terminal oxygen atoms from the iodate anions. The Raman spectra have been collected for these metal iodates; In(IO₃)₃ was found to display a distinctively different vibrational profile than Al(IO₃)₃ or Ga(IO₃)₃. Hence, the Raman profile can be used as a rapid diagnostic tool to discern between the different structural motifs.     

Preparation, crystal structure and chemical bonding analysis of the new binary compounds Rh4Ga21 and Rh3Ga16

The two new binary compounds Rh₄Ga₂₁ (space group Cmca (Cmce), , , , Pearson symbol oC136) and Rh₃Ga₁₆ (space group Ccca (Ccce), , , , Pearson symbol oC76) were synthesised and their crystal structures were solved from single-crystal X-ray diffraction data. From a topological point of view, both these two crystal structures and the crystal structure of PdGa₅ can be described either as inhomogeneous intergrowth structures containing three different kinds of segments, or as built up by layers of capped square antiprisms condensed via their capping atoms. Bonding analysis with bonding indicators revealed that the crystal structures of Rh₄Ga₂₁ and Rh₃Ga₁₆ have to be considered as framework polyanions formed by covalently bonded gallium atoms with embedded rhodium cations.     

A novel cesium hydroxygallophosphate with a layered structure built up of rutile ribbons: CsGa2(OH)2[(PO4)H(PO4)]

A new cesium gallophosphate, CsGa₂(OH)₂[(PO₄)H(PO₄)], with an original layer structure has been synthesized by hydrothermal route and characterized by single-crystal X-ray diffraction (R=0.0344, R_w=0.0319). Its structure crystallizes in the monoclinic space group P2₁/a with cell parameters , , , β=93.36(4)° and Z=2. It consists of [Ga(OH)PO₄]_∞ layers built up of rutile ribbons interconnected through PO₄ tetrahedra. The structure of CsGa₂(OH)₂[(PO₄)H(PO₄)] is closely related to those of (NH₄)Ga(OH)PO₄ and (en)Ga₂(OH)₂(PO₄)₂ (en=ethylenediamine [H₃N(CH₂)₂NH₃]²⁺). The three structures differ mainly from each other by the relative positions and the spacing of the successive layers, which are governed by different hydrogen bonding modes between [Ga(OH)PO₄]_∞ layers and the interleaved species. The title compound presents strong symmetric hydrogen bonds O---H---O which bridge two PO₄ tetrahedra of two successive layers. As a consequence, the distance between the layers is significantly shorter than in the two other amine compounds.     

A first-principles surface phase diagram study for Si-adsorption processes on GaAs(1 1 1)A surfaces

The adsorption processes of an Si atom on GaAs(1 1 1)A surfaces under growth conditions are investigated on the basis of first-principles surface phase diagrams, in which adsorption-desorption behavior is described by comparing the calculated adsorption energy obtained by total-energy electronic-structure calculations with vapor-phase chemical potential estimated by quantum statistical mechanics. The calculated surface phase diagram as functions of temperature and As₂ pressure demonstrates that both Ga and As atoms are adsorbed on the Ga-vacancy site of GaAs(1 1 1)A-(2×2) surface under low As-pressure conditions, resulting in the formation of (2×2) surface with an As adatom. The surface phase diagrams as functions of temperature and Si pressure also reveal that an Si atom can be adsorbed on the (2×2) surface with an As adatom for temperatures less than ∼1160 K and this Si atom can occupy one of As-lattice sites after the incorporation of another As atom, leading to p-type conductivity. In contrast, the (2×2) surface with an As trimer is found to be stabilized under high As-pressure conditions. The surface phase diagram for Si incorporation clarify that an Si atom can be adsorbed at one of Ga-lattice sites of the (2×2) surface with an As trimer for temperatures less than ∼870 K. These calculated results provide one of possible explanations for the formation of p-type and n-type GaAs on GaAs(1 1 1)A surfaces under low and high As-pressure conditions, respectively.     

Investigation of etch characteristics of non-polar GaN by wet chemical etching

We characterized the surface defects in a-plane GaN, grown onto r-plane sapphire using a defect-selective etching (DSE) method. The surface morphology of etching pits in a-plane GaN was investigated by using different combination ratios of H₃PO₄ and H₂SO₄ etching media. Different local etching rates between smooth and defect-related surfaces caused variation of the etch pits made by a 1:3 ratio of H₃PO₄/H₂SO₄ etching solution. Analysis results of surface morphology and composition after etching by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) demonstrated that wet chemical etching conditions could show the differences in surface morphology and chemical bonding on the a-plane GaN surface. The etch pits density (EPD) was determined as 3.1 × 10⁸ cm⁻² by atom force microscopy (AFM).     

Influence of deposition temperature on morphological, optical, electrical and opto-electrical properties of highly textured nano-crystalline spray deposited CdO:Ga thin films

This study investigated the effect of deposition temperature on the morphological, optical, electrical and opto-electrical properties of CdO:Ga films prepared by a cost effective spray pyrolysis deposition method. The substrate temperature was varied from 275 to 375 °C, in steps of 25 °C. The XRD patterns reveal that films are polycrystalline with cubic structure and are highly textured along (2 0 0) preferential orientation. The crystallinity and crystallite size increases with deposition temperature. The SEM images confirmed these results and showed larger grains and more crystallization for the higher deposition temperature. The electrical studies show degenerate, n-type semiconductor nature with minimum resistivity of 1.93 × 10⁻⁴ Ω cm. Temperature dependence of electrical conductivity shows a semiconducting behavior with a spectrum of activation energy. The electrical conductivity of the film dependence of temperature shows the thermally activated band conduction mechanism. The optical gap varies from 2.54 to 2.74 eV. The highest figure of merit observed in the present study is 9.58 × 10⁻³ Ω⁻¹ and shows improvement than our previous reports. The blue shift of absorption edge (or bandgap widening BGW) can be described by the Moss-Burstein (M-B) effect in which the optical absorption edge of a degenerate n-type semiconductor is shifted towards higher energy.     

Photoemission study of samarium on and CdTe(1 0 0)

Experimental photoemission results on and CdTe(1 0 0) surfaces on a function of samarium adsorbate coverage are presented. Energy distribution curves were recorded at photon energies around the Sm 4d→4f threshold (135–136 eV) to reveal the Sm contribution to the electronic structure and enhance the sensitivity. The evolution of core-level Ga 3d and Cd 4d spectra was also studied. The interaction of Sm with both GaN and CdTe leads to reactive interface formation. In the case of CdTe, it results in creation of an interfacial Sm–CdTe compound, which inhibits further diffusion of Sm into the bulk. The interaction of Sm with GaN leads to the release of Ga atoms on the surface and segregation of Ga clusters.     

Aluminum(I) and Gallium(I) Compounds: Syntheses,Structures, and Reactions

By the end of the last century there were already the first indications of the possible existence of Al¹ halides. However, it was only through the pioneering works of W. Klemm, who would have celebrated his 100th birthday on January 6, 1996, that detailed spectroscopic investigations became possible. Since the end of the 1970s the reactivity of AlX and GaX species in solid noble gases has been confirmed by numerous examples. In recent years formally monovalent Al and Ga species have been successfully synthesized on a preparative scale. In addition to the first halides, organometallic compounds with metal–metal bonds have been isolated and investigated with regard to their chemical properties. The fundamental importance of such species has been documented in this journal among others in the form of two highlight articles in which experimental and theoretical aspects have been examined with examples, and parallels and differences with respect to boron chemistry have been illustrated. This review is intended to give an account of the chronological development of this research area over the last few years, but an attempt is also made to categorize the experimental results achieved not only with respect to structure, thermodynamics, and reactivity, but also with the aid of quantum chemical calculations and by comparative considerations.