Thin Ga Research Articles

Oxidation of CoGa(110)

The interaction of oxygen (O 2) with CoGa(110) has been studied by means of high-resolution electron energy loss spectroscopy (EELS), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). At 300 K, an amorphous Ga oxide grows, which transforms into an ordered structure at 770 K. A thin well-ordered Ga oxide layer also grows at this ordering temperature. The LEED pattern of the well-ordered Ga oxide corresponds to a structure with small distortion from a hexagonal arrangement. The EEL spectrum exhibits four losses at 305, 470, 605 and 745 cm −1 which are characteristic for Ga 2O 3. The EEL spectrum can be reproduced by calculations based on the dielectric theory by using IR parameters of Ga 2O 3. The thickness of the film is estimated to be about 10 Å.

Electrical conductivity, thermal expansion and reaction of (La, Sr)(Ga, Mg)O 3 and (La, Sr)AlO 3 system

The electrical conduction, thermal expansion, chemical reaction, and texture of a sintered body were measured for the mixture of (La, Sr)AlO 3 and (La, Sr)(Ga, Mg)O 3, and on the Al-substituted (La, Sr)(Ga, Mg, Al)O 3. No enhancement effect was observed with electrical conductivity by mixing or doping of the Al component. These systems showed lower electrical conductivity than the proportional value of the components. It was considered that the difference of thermal expansion stays at a tolerable level. The grain growth inhibition suggested the strengthening effect of mixing (La, Sr)AlO 3 into (La, Sr)(Ga, Mg)O 3. From these results, it is expected that (La, Sr)AlO 3 can be used as an electrolyte-protective layer material in order to make a co-fire process possible. In this co-fire, a thin (La, Sr)(Ga, Mg)O 3 electrolyte film will be protected by a very thin (La, Sr)AlO 3 film and supported on a Ni-ceramic anode substrate tube or plate. Such a very thin electrolyte will be effective for cost reduction by decreasing the use of Ga.

Semiconductor Properties of Thin and Thick Film Ga 2O 3 Ceramic Layers

The semiconductor behavior of thin and thick film β Ga 2O 3 layers is studied by measuring the resistivity as a function of oxygen partial pressure and temperature in the range up to 900°C. As for ZnO and SnO 2 a relatively high initial oxygen vacancy defect concentration has to be assumed for β Ga 2O 3. However, the conductivity is by many orders of magnitude lower and the activation energy by about 1 order of magnitude higher. With increasing temperature a change at about 810±50°C from a lower value of the activation energy E A(2)=1·6 ± 0·1 eV to a higher one E A(1)=2·4 ± 0·1 eV is observed at thin film ceramic layers thus leading to the assumption that oxygen cleavage in contact with the atmosphere is achieved in the upper range. Contrary to the band model which is convincingly founded for ZnO and SnO 2 in the literature, polaron hopping seems to be the more suitable model for analysis of the conductivity data of β Ga 2O 3. The lower value E A(2) is interpreted as the polaron hopping energy at approximately constant charge carrier concentration. On the other hand, in the high temperature range above T ch the charge carrier density is varying. However, at the applied measuring conditions, this variation remains below the initial oxygen vacancy defect concentration. Corresponding to formula I Ga III 2-2xGa II 2x ′O 3-xV { O,x} and formula II Ga III 2-xGa I x ″O 3-xV { O,x} two different structures for the oxygen vacancy defects in β Ga 2O 3 are discussed. The measurements seem to confirm formula I. However, provided that there is an equilibrium between states corresponding to formula II and I, the assumption of double occupied Ga I states is also consistent with the experimental results.

Kinetics of gallium films confined at grain boundaries

We report on a combined study, by in situ x-ray diffraction at temperatures between 293 and 80 K, differential scanning calorimetry, and coherent quasielastic neutron scattering (QENS), of thin Ga films confined at grain boundaries in ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}\ensuremath{-}\mathrm{G}\mathrm{a}$ nanocomposites that are produced by high-energy ball milling. We find that a molar fraction of Ga of up to 0.18 does not undergo phase change in the temperature interval investigated, which contains the bulk melting temperature ${T}_{M}^{\mathrm{bulk}},$ and conclude that this Ga is located in confined layers at grain boundaries, with an estimated thickness of six atomic monolayers. In samples with a higher overall molar fraction, the Ga in excess of molar fraction 0.18 melts and crystallizes reversibly when cycled between 100 and 320 K. For such samples, QENS at 320 K, that is, 17 K above ${T}_{M}^{\mathrm{bulk}},$ indicates three distinct diffusion coefficients $D$ for Ga: one below the resolution limit, ${D}_{1}<1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}{\mathrm{cm}}^{2}/\mathrm{s},$ one agreeing with the bulk liquid value, ${D}_{2}=3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}{\mathrm{cm}}^{2}/\mathrm{s},$ and a faster coefficient ${D}_{3}=2.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}{\mathrm{cm}}^{2}/\mathrm{s}.$ We argue that the smaller and medium diffusion coefficients, ${D}_{1}$ and ${D}_{2},$ represent, respectively, solidlike layers near the ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}\ensuremath{-}\mathrm{G}\mathrm{a}$ interface and liquid Ga in the core of interfacial layers and in liquid droplets. The fast diffusion coefficient ${(D}_{3})$ may be due to diffusion on free surfaces.

Selective detection of methane in domestic environments using a catalyst sensor system based on Ga2O3

Abstract Using high temperature operated Ga 2 O 3 thin films, attempts have been made to realize sensors for methane detection with high stability and reproducibility and quick response. Yet these sensors show high cross sensitivities to ethanol (300 ppm) and other organic solvents that distinctly exceed the measurement effect towards methane (0.5%). Using a thin film Ga 2 O 3 -gas sensor which is equipped with a catalytic-preoxidation-filter of porous Ga 2 O 3 and operated at temperatures of 800°C, the cross sensitivities are eliminated. The organic solvents are oxidised while passing the filter and only the quite stable methane is allowed to reach the sensor surface. Selective CH 4 detection is possible, even in the (simultaneous) presence of 300 ppm ethanol.

Over 10% efficient CuInS 2 solar cell by sulfurization

The solar cell, which consists of a CuInS 2 thin film prepared by sulfurization of a metallic precursor deposited either on a Pt sheet or a Mo-coated soda lime glass substrate, exhibited an efficiency of 10.5% at air mass 1.5 without antireflection coating. When the latter is used as a substrate, an initially more Cu-rich film was often torn off from the substrate. The film's adhesion to it was significantly improved by introducing a very thin Ga layer between the Mo surface and a stacked Cu In precursor layer. A heterojunction solar cell of the comparable efficiency was obtained using this adherent thin film.

Mobility of Ga confined in nanostructured alumina

The melting behavior of thin Ga films confined at the grain boundaries of nanostructured alumina was investigated by DSC. At temperatures near T m part of the Ga film is molten whereas about six monolayers remain solid even 20 K above T m. The diffusion of the Ga was investigated by means of QENS. The molten Ga film exhibits a lower diffusivity than bulk liquid Ga. This is rationalised in terms of the confined geometry.

Substrate orientation dependence of the growth of GaSe thin films on GaAs

The initial stages of the heteroepitaxial growth of GaSe thin films on GaAs(001), (111)A and (111)B surfaces have been studied by means of LEELS (low-energy electron-loss spectroscopy) and AFM (atomic force microscopy). GaSe films were grown on the substrates at 400°C using a single evaporation source of GaSe. The evolution of a LEELS spectrum with increase in film thickness reveals a difference in deposition depending on the surfaces. While only GaSe grows on GaAs(111)A and (111)B surfaces, the GaAs(001) surface first undergoes a deposition of Ga 2Se 3; subsequently GaSe grows on the thin Ga 2Se 3. In the AFM images of films with thickness of about 20 Å on GaAs(111)A and (111)B surfaces, steps with a height of a primitive layer thickness of GaSe are observed, thereby suggesting a primitive layer-by primitive layer growth of GaSe.

MOCVD growth of Ga 2Se 3 on GaAs(100) and GaP(100): a Raman study

Due to its luminescence in the blue-green spectral range, Ga 2Se 3 has become a subject of extensive research. Thin epitaxial Ga 2Se 3 layers were grown on GaAs(100) and GaP(100) for the first time by metalorganic chemical vapour deposition (MOCVD). The structural and optical properties were investigated by transmission electron microscopy, Raman spectroscopy and photoluminescence (PL). Raman spectra were taken in a temperature range from 100 K to 600 K using excitation energies of Ar + and Kr + ion lasers. Additionally the photoluminescence of the layers was measured using ultraviolet (UV) excitation. The results of this study are compared and discussed with those of other growth techniques.

Surfactant induced growth of thin gallium films on an insulating (sapphire) substrate

It was shown that Sb may be used as a surfactant to modify the growth of thin Ga films on a sapphire substrate. A continuous film can be grown at a small thickness, whereas without the surfactant the film grows in the form of highly dispersed isolated droplets even if the film thickness reaches more than 120 nm.

Carrier Tunneling in High Magnetic Fields

Proceedings of the XXIV International School of Semiconducting Coinpounds, Jaszowiec 1995. A magnetic field induced coupling is observed between the Landau levels with different quantum number of two GaAs quantum wells separated by a thin (Ga,Al)As tunnel barrier using magneto-photoluminescence-excitation spectroscopy. This coupling cannot be due to a resonance between single particle energy levels, and therefore an explanation is proposed in terms of the Coulomb interaction of magneto-excitons across the thin barrier.

X-ray characterization of very thin [formula omitted] layers grown on InP

High resolution X-ray diffraction has been successfully used to study structural configuration of very thin Ga x In 1−x P (x ≈ 0.5) embedded in InP, grown by low-pressure metal-organic vapor-phase epitaxy. Both superlattice and single-strained-layer structures with various Ga 0.5In 0.5P layer thicknesses were investigated. The layer thickness, composition and interface grading have been determined. A graded Ga x In 1−x P film was identified in the Ga 0.5In 0.5 P- InP upper interface of all samples presented in in this paper, while the lower interface is kept relatively sharp. Our observation can be explained by Ga-component segregation from the Ga 0.5In 0.5P layer into the following InP layer. The dependence of the dimension of graded interlayer on Ga 0.5In 0.5P thickness and the growth rate of Ga 0.5In 0.5P film in the range of coherent growth were evaluated. It is shown that the X-ray diffraction method combined with the computer simulation based on the dynamical diffraction theory is a sensitive tool to study not only uniform but also graded layers quantitatively. Scanning transmission electron microscopy measurements were carried out for comparison, clearly proving the X-ray results.

Determining lattice mismatch or the composition of a single ultra thin GaInAs layer grown on InP

A high resolution measuring method to determine lattice mismatch or the composition for a single ultra thin Ga x In 1− x As ternary layer is discussed. The maximum errors of lattice mismatch and composition x depend strongly on the uncertainty of band-offset and are, respectively, ±0.10% and ±0.01 in the case of a two-monolayer GaInAs single quantum well for band-offset uncertain at a conduction band of ΔE c = 0.42 ± 0.02 eV. The accuracy of this method is also calibrated using an X-ray diffraction technique for multiple quantum well structures of two-monolayer thick wells grown by digital epitaxy. This method may also be applied to GaInAsP quaternary.

Fractal growth of Ga 6Mn phase in thin Ga 97Mn 3 amorphous films

Geometric patterns formed after crystallization of GaMn amorphous films with Ga-rich compositions higher than about 80 at.% Ga were investigated by means of transmission electron microscopy. Two basically different types of the patterns were found to occur depending on the composition of the amorphous films. One, observed upon crystallization of the Ga 6Mn phase from the Ga 97Mn 3 amorphous, was composed of random ramified branches which are very similar to those formed by diffusion-limited aggregation (DLA) in two dimension, and showed the fractal dimension of D = 1.7. Another pattern was developed upon crystallization of the Ga 81Mn 19 amorphous, exhibiting a dense radial distribution of Ga 4Mn crystallites, which resembled the Eden cluster with a non fractal character. Materials parameters affecting the pattern formation are discussed.

Optical properties and electronic structure of thin (Ga,In)As-AlAs multiple quantum wells and superlattices under internal and external strain fields.

We report on studies of the optical properties of a series of (Ga,In)As-AlAs thin strained-layer multiple quantum wells and superlattices submitted to high uniaxial stress perpendicular to the growth axis of the structures. Samples having both type-I and type-II configurations for their conduction-band to valence-band potential profiles have been studied. Explanation of the experimental data has been made in the context of an envelope-function approach, which explicitly takes into account the mixing of the upper valence-band states with the split-off valence-band states. The inclusion of spin-dependent deformation potentials is necessary to interpret the values of the zero-stress energies as well as to explain their behavior as a function of the external stress.

Modulation spectroscopy characterization of MOCVD semiconductors and semiconductors structures

This paper reviews recent developments in the use of contactless modulation spectroscopy to yield important information about MOCVD growth as well as the properties of MOCVD fabricated semiconductors and semiconductor microstructures. The method of reflectance difference spectroscopy can be used to gain significant insights into chemical and structural parameters during actual growth conditions. The electromodulation technique of photoreflectance (PR) probes the electronic states of the material. It has many applications for in-situ post-growth characterization of crystal quality, very thin Ga 1-xAl xAs/GaAs epitaxial layers, Ga 1−xAl xAs alloy composition, deep trap states, surface electric fields and carrier concentrations, lattice-mismatch strain, etc, as well as the determination of relevant parameters of heterojunction structures. In addition, recent PR experiments at 600°C on GaAs and Ga 0.82Al 0.18As show potential for in-situ monitoring during growth.

Thin-film topography control with transient liquid underlayer

A novel and effective technique for fabricating metal surfaces with controlled topography is described. The metal of interest is deposited onto a thin (25–200 Å) underlayer of a liquid metal. Transient liquid reactions during film growth and coalescence lead to characteristic roughening of the deposits. Studies of 1-μm Al films deposited on thin Ga underlayers revealed a consistent increase of the size of Al features with the average thickness of the Ga underlayer. No apparent change in the films’ resistivity was detected. Limited studies of 1-μm Cu films with a Ga underlayer suggest the general applicability of this technique.

Growth and transport properties of (Ga,Al)Sb barriers on InAs

We have investigated the transport properties of (Ga,Al)Sb–InAs heterostructures grown by molecular-beam epitaxy with the Al composition in the range of 0.3–0.5 where the alloy serves as a potential barrier for electrons in InAs. Field effect capacitors using a thick (Ga,Al)Sb barrier demonstrate the modulation of carrier densities in InAs by the application of an electric field. In the region of thin (Ga,Al)Sb, where tunneling becomes dominant, a novel negative resistance appears in InAs/(Ga,Al)Sb/InAs single-barrier structures due to the specific band alignment of this system. The results have been further elucidated under a magnetic field.

Détermination de l'épaisseur et de la concentration des couches minces épitaxiales Ga 1− xAl xAs/GaAs par la méthode des sauts de la photoémission

The analytical expression of the quantum efficiency of the external photoelectric effect is established for a photocathode formed by juxtaposition of a thin film and a substrate. The thickness and the atomic composition of the thin Ga 1− x Al x As films, deposited by liquid phase epitaxy onto a GaAs(100) substrate, are determined by the X-ray photoemission jumps method. This method is based on the measurement of photoemission jumps at the absorption K edges of the elements constituting the photocathode. The results of measurements of the thickness of thin Ga 1− x Al x As films and their concentration are compared with the technological conditions of fabrication on the one hand and the behaviour characteristics of photocurrent spectra on the other.

Core level photoemission study of the interaction of plasmas with real GaAs(100) surfaces

Photoemission is used to study the interaction of H 2 (for oxide removal) and N 2 (for nitridation) plasmas with native oxide covered GaAs(100) surfaces. H 2 plasmas completely suppress the As oxide but leave a substantial amount of Ga oxide on the surface. A thin (2 nm) Ga and As nitride layer is formed by exposure to an N 2 plasma. In contrast with plasma nitrided MBE grown surfaces, no significant (above 0.2 eV) Fermi level movement is induced by this treatment.