Good Structural Quality Research Articles

Thermal and plasma nitridation of GaSe crystal

The possibility of the nitridation of gallium selenide followed by the GaN growth is demonstrated. We used the partial pressures diagram method to study the equilibria during the GaSe thermal nitridation process. Experimentally we obtained the wurtzite GaN by the nitridation of GaSe in NH 3 flow in the temperature range 1000–1200 K for 1 h exposition. GaN was also obtained using low temperature ammonia plasma processing of GaSe at p NH 3 =0.13 Pa. X-ray diffraction measurements show that GaN grew textured with the (1 1 0) plane being parallel to the (0 0 1) plane of GaSe but the layers of the good structural quality were also obtained. Luminescence properties of all samples have been examined.

Surface structure induced by Ar +-bombardment of decagonal AlNiCo

We have investigated the surfaces of decagonal AlNiCo single quasicrystals in UHV by Reflection High Energy Electron Diffraction (RHEED), Atomic Force Microscopy (AFM) and Auger Electron Spectroscopy (AES). The surfaces were prepared by Ar +-sputtering and annealing. We observe well-defined RHEED patterns directly after sputtering at room temperature, revealing a ten-fold symmetry with respect to the azimuthal angle of the incident beam. Two patterns occur, alternating every 18°. This symmetry behaviour is probably caused by a bcc overlayer consisting of multiple domains in different orientations. The RHEED patterns show a strong temperature dependence. A spontaneous phase transition into a quasiperiodic structure is observed upon annealing to about 350 °C. RHEED patterns of a flat, quasicrystalline surface of good structural quality are observed after sputtering at 400 °C. As indicated by AES, the influence of oxygen on the structural behaviour seems to be important.

Phason fluctuations in i-AlPdRe and i-CdYb phases

We present a high resolution X-ray diffraction study on two single grain phases: the i-AlPdRe phase which is supposed to be isostructural to the i-AlPdMn one and the new binary CdYb phase. Both the Bragg peak width (sensitive to uniform phason strain distribution) and the diffuse scattering (sensitive to long wavelength phason fluctuations) have been studied. In the i-AlPdRe phase, we find an anisotropic distribution of diffuse scattering intensity around the Bragg peaks. Its intensity is related to Q per, demonstrating its relation to phason fluctuations. The amount of diffuse scattering is similar to what was previously found in the AlPdMn phase, but the shape anisotropy is markedly different. The i-CdYb phase presents a good structural quality. Its Bragg reflection shows an isotropic broadening which scales with Q per, as a consequence of uniform phason strain distribution with a magnitude similar to what was found in the i-ZnMgRe phases. There is also a clear anisotropic distribution of diffuse scattering intensity located around the Bragg peaks. It is related to long wavelength phason fluctuations with an anisotropy pointing toward a threefold type instability.

Kinetic growth conditions maintaining lateral superlattice structures

Kinetic Monte Carlo simulations of thin film growth during co-deposition of two model elements, A and B, on the striped substrate surfaces of A and B have been performed with changing the substrate temperature and the interatomic interactions in order to find out critical features maintaining the lateral superlattice structures during the film growth. Only the kinetic aspects are examined and the strain effect is not taken into account explicitly. Large barrier asymmetry for the jumps across the border of the stripes and large probability of detachment from wrong places are found to be essential to the good structural quality of the film.

Growth and Characterization of ZnMgSe Alloys and ZnSe/ZnMgSe Multi-Quantum Wells

ZnMgSe alloys and ZnSe/ZnMgSe multi-quantum well (MQW) structures were grown on GaAs (001) substrates by solid-source molecular beam epitaxy (MBE). It was found that the content of Mg in ZnMgSe alloys can be well controlled by adjusting the beam fluxes of element sources. X-ray reflection spectra from MQWs revealed strong satellite peaks, indicating good structural quality. Due to the quantum confinement effect, the photoluminescence (PL) peaks from the MQWs were shifted with variation in well width. Small Stokes shifts were identified between the transition energies observed by PL and reflectance. The interaction between excitons and LO phonons in ZnSe/ZnMgSe MQWs was greatly reduced compared with that in ZnSe bulk.

Morphology and surface reconstructions of m-plane GaN

ABSTRACTM-plane GaN(1100) is grown by plasma assisted molecular beam epitaxy on ZnO(1100) substrates. A low-temperature GaN buffer layer is found to be necessary to obtain good structural quality of the films. Well oriented (1100) GaN films are obtained, with a slate like surface morphology. On the GaN(1100) surfaces, reconstructions with symmetry of c(2×2) and approximate “4×5” are found under N- and Ga-rich conditions, respectively. We propose a model for Ga-rich conditions with the “4×5” structure consisting of ≥ 2 monolayers of Ga terminating the GaN surface.

Optimisation of industrial wastes reuse as construction materials.

This study concerns the reuse of two inorganic wastes, foundry residues and fly ashes from municipal solid waste incineration, as "recycled aggregate" in concrete production. This kind of reuse was optimised by waste treatment with the following steps: waste washing with water; waste stabilisation-solidification treatment with inorganic reagents; final grinding of the stabilised waste after curing for about 10-20 days. Both the treated wastes were reused in concrete production with different mix-designs. Concrete specimens were characterised by means of conventional physical-mechanical tests (compression, elasticity modulus, shrinkage) and different leaching tests. Experimental results showed that a good structural and environmental quality of "recycled concrete" is due both to a correct waste treatment and to a correct mix-design for concrete mixture.

Growth modes and microstructures of ZnO layers deposited by plasma-assisted molecular-beam epitaxy on (0001) sapphire

Transmission electron microscopy and high resolution x-ray diffraction are used to characterize defects in ZnO layers grown by plasma-assisted molecular-beam epitaxy on (0001) sapphire. Two- and three-dimensional types of growth modes are described and the observed mosaic structure is analyzed in each case. It is found that two-dimensional layers exhibit a roughness as low as 6 nm. Their subdomains have small lateral coherence lengths and a mean in-plane misorientation of ±0.4°, leading to an important dislocation density of 1–4×1010 cm−2. On the contrary, it is demonstrated that, through numerous interactions between dislocations, the three-dimensional growth mode leads to a better structural quality with a larger lateral coherence length and a smaller in-plane mosaic spread of ±0.07°. The total dislocation density is consequently reduced by 1 order of magnitude down to 3–5×109 cm−2 and the radical modification of the structure results in a change of the dislocation distribution. Our results thus demonstrate that two-dimensional growth mode and low full width at half maximum for symmetric x-ray diffraction are a not reliable indicator of a good structural quality.

Electrical Characterization of Al/SiNx:H/n and p-In0.53Ga0.47As Structures by Deep-Level Transient Spectroscopy and Conductance Transient Techniques

We have analyzed the influence of the dielectric composition and the post deposition rapid thermal annealing (RTA) treatment on the electrical characteristics of electron-cyclotron-resonance plasma-deposited SiNx:H/n and p-In0.53Ga0.47As interfaces. The devices are characterized by means of capacitance–voltage (C–V), deep-level transient spectroscopy (DLTS) and conductance transient analyses. Our results show that a simple cleaning step of the semiconductor surface prior to insulator deposition, and a post deposition RTA process are sufficient to obtain good-quality structures, the n-type being better than the p-type. In both cases, we conclude that a dielectric composition of x=1.50 seems to be the best choice, and that the most adequate RTA temperature is between 500°C and 600°C.

A new GaAs material for X-ray imaging

It is now recognized that X-ray imaging, in particular for medical applications, could be achieved using GaAs detectors provided that it will be possible to grow epitaxial layers at low cost, of large enough thickness (100–300 μm), and low enough doping (10 13–10 14 cm −3). The aim of this communication is to describe a growth technique, cheap to assemble and run compared to conventional growth techniques, which allows to grow in few hours epitaxial layers of good structural, electrical and optical qualities, with thicknesses ranging from 100 to 500 μm. Doping achieved without taking any precaution concerning contamination is about 10 15 cm −3. The electrical characteristics of these layers, as well as the Schottky barriers made on them will be briefly described. We discuss and illustrate with experimental data the means by which the doping can be reduced (by increasing the As antisite concentration through a variation of the growth rate, by decreasing the contamination and by electron irradiation).

Potential of thick GaAs epitaxial layers for pixel detectors

It is now recognised that X-ray imaging, in particular for medical applications, could be achieved using GaAs detectors provided that epitaxial layers of large enough thickness, and low enough doping can be grown at low cost. The aim of this communication is to describe a growth technique, that is cheap to mount and run compared to conventional techniques, with which epitaxial layers of good structural, electrical, and optical quality, with thickness ranging from 100 to 500 μm can be obtained. Residual doping achieved, without taking any precaution concerning contamination, is in the range 10 14–15 15 cm −3. The electrical characteristics of these layers, as well as Schottky barriers made on them, are described, discussed, and illustrated with experimental data, a mean by which the doping can be reduced, namely electron irradiation.

BeCdSe as a ternary alloy for blue-green optoelectronic applications

Bulk BeCdSe layer lattice-matched to a GaAs substrate, as well as a BeCdSe/ZnSe quantum well (QW) structure have been grown using the submonolayer digital alloying mode of molecular beam epitaxy. The structures have demonstrated bright photoluminescence up to room temperature and good structural quality. Stimulated emission under optical pumping has been obtained for a 2 nm BeCdSe/ZnSe multiple QW structure at 80 K. The bowing parameter of the energy gap of this ternary alloy has been estimated as about 4.5 eV.

CdTe epilayers for uses in optical waveguides

CdTe epilayers have been grown by vapor phase epitaxy (VPE) on glass, MgO, sapphire, LiNbO3 and mica substrates. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies show the good structural quality of the epilayers. In these epilayers, a few optical modes were excited with a 1.33-μm laser. The measured propagation losses were in the range between 5 dB/cm and less than 0.5 dB/cm. From dark-mode m-lines, the epilayer thickness was found to be in the 1–3 μm range, in good accord with that obtained by SEM measurements. The refractive index obtained from the fitting is also in good accord with that of bulk CdTe.

Metalorganic vapor-phase epitaxy of ZnMgCdSe structures on InP

Metalorganic vapor-phase epitaxy of ternary ZnMgSe layers and, for the first time, quaternary ZnMgCdSe superlattices is presented. Lattice-matched Zn 0.14Mg 0.86Se with a high magnesium content x and a good structural quality was achieved by introducing a lattice-matched ZnCdSe buffer and phosphorus stabilisation during InP deoxidation. We obtained a rocking curve half-width below 100 arcsec for a 300 nm thick layer with x=0.86. Lattice matching on InP was achieved for ZnMgCdSe layers with magnesium concentrations from 38% to 68%, corresponding to a bandgap of 2.9 and 3.4 eV, respectively. An overall optical gain of 35 cm −1 was observed in a ZnMgCdSe superlattice structure.

Magnetic Properties and GMR of Sputtered Permalloy/Au Multilayers

We report on structural, magnetic, and GMR properties of permalloy/Au multilayers where permalloy = Ni83 Fe17 , deposited by face-to-face sputtering onto Si(111) substrate. X-ray diffraction studies confirmed a good structural quality of our multilayers. The samples were characterised with vibrating sample magnetometer, longitudinal magnetooptical Kerr effect and giant magnetoresistance measurements. It was determined that our multilayers are magnetically very soft with Ηc 1 Oe and show uniaxial anisotropy with Ηι' 5 Oe. For gold sublayer thickness dΑ close to 1.1 nm the antiferromagnetic coupling is present in very narrow Au thickness range ( ≈ 0.2 nm). Despite a good structural quality of samples relatively small giant magnetoresistance value (1.2% at room temperature) was found. It is due to non-perfect aniferromagnetic coupling caused by pinholes.

Metal organic vapor phase epitaxy of GaAsN/GaAs Quantum wells using Tertiarybutylhydrazine

GaAsN epilayers and quantum wells with a good structural quality and surface morphology were grown by low pressure metal organic vapor phase epitaxy using tertiarybutylhydrazine as a novel nitrogen source. The dependence of nitrogen incorporation on growth temperature was studied for epitaxy with arsine and tertiarybutylarsine precursors. A nitrogen content of 6.7 % was achieved using tertiarybutylhydrazine and tertiarybutylarsine at a low growth temperature of 530 °C. The observed room temperature luminescence shows an increasing redshift with increasing nitrogen contents of the wells.

Micro Defects in Nearly Dislocation Free GaN Doped with Mg during High Pressure Crystallization

GaN crystals grown from solutions of liquid gallium alloyed with Mg, at high pressure of nitrogen, are highly resistive and of very good structural quality, evidenced by X-ray diffraction measurements. The high structural quality of these crystals is also confirmed by selective etching of the N-polar (000—1) surface in molten KOH–NaOH eutectic which results in EPD as low as few tens on cm2. On the other hand, the etching of the Mg-doped crystals in the hot mixture of H3PO4 and H2SO4 beside the etch pits corresponding to dislocations, results in etch hillocks which are not observed for crystals grown without Mg. The hillocks are often arranged into periodic arrays corresponding to growth macrosteps on the crystal surface. In order to identify defects responsible for such etching results the crystals were studied by TEM. The measurements confirmed that the crystals are free of grown-in dislocations, however, bands of microdefects have been observed. Their correlation with the etching results will be shown and discussed in the paper.

Structure and Surface Properties of Metalorganic Vapor Phase Epitaxial CdTe and HgCdTe(111)B Layers Grown on Vicinal GaAs(100) Subatrates

We achieved the HgCdTe(111)B layer with a specular surface and high structural quality, which was the candidate material for IRFPA application, on GaAs(100) by metalorganic vapor phase epitaxy. To realize such superior layers, we studied the structure and surface morphology of CdTe and HgCdTe(111)B with concerning the growth mechanism. We found twins in CdTe were originated both at the CdTe–GaAs interface and during the subsequent CdTe growth. These twins could be eliminated by using misoriented substrates and adjusting the VI/II ratio conditions. Suitable conditions for suppressing twins also improved the CdTe surface morphology. We clarified the CdTe crystal perfection was improved effectively by decreasing the growth rate. This attractive CdTe buffer was necessary for a twin-free HgCdTe(111)B layer whose dislocation density was small. We obtained HgCdTe layers with good structural quality and smooth surface morphology under the large VI/II ratio condition, similar to the case of CdTe growth.

Plasma doping for shallow junctions

In this article we review the characteristics of ultrashallow junctions produced by plasma doping (PLAD). PLAD is one of the alternate doping techniques being developed for sub-0.18 μm devices. Here, we describe results from a wide range of experiments aimed at the production of ultrashallow junctions. For the results shown here, a BF3 plasma was used to provide the dopant ions that were implanted into 150 and 200 mm Si substrates using wafer biases ranging from −0.14 to −5.0 kV. The ultrashallow junctions formed with this technique have been examined with both secondary ion mass spectrometry and electrical profiling techniques. Good sheet resistance uniformity, charging performance, structural quality, and photoresist integrity have been obtained. When PLAD is used in the production of sub-0.2 μm gate length p-metal–oxide–semiconductor field effect transistors, one finds subthreshold swing, off-state leakage, and hot-carrier reliability that are similar to beamline-implanted ones. In addition, higher drive currents are seen in the plasma-doped devices.

Structural characteristics of [formula omitted]-axis-oriented PrBa 2Cu 3O 7 thin films grown by pulsed laser deposition

PBCO films have been successfully fabricated at different temperatures. X-ray diffraction results show that the orientation of PBCO films varies with decreasing deposition temperature. The optimal deposition condition for a-axis oriented PBCO films is 15 Pa oxygen pressure and 700°C. Raman scattering measurements indicate that the 514 cm −1 of A g phonon mode can be used as a criterion for determining whether the film is a-axis-oriented or not, e.g., the intensity of 514 cm −1 mode is the strongest for c-axis-oriented film but almost disappears for a-oriented film. High-resolution transmission electron microscopy confirms that our a-axis-oriented film has a good structural quality.