Chromium diffusion coefficients in alumina single crystals were evaluated from penetration profiles determined by the SIMS technique. The samples were previously annealed at 1000°C (1 hour), 1500°C (4 hours), and 1700°C (24 hours). Diffusion experiments were carried out at 1400°C during 10 hours. The results show that bulk diffusion coefficients are strongly dependent on preannealing conditions (temperature and time): they decrease by more than an order of magnitude when the preannealing temperature is increased from 1000°C to 1700°C. These results are discussed taking into account the dislocations and point defects in alumina. We consider the role played by the linear defects resulting from surface polishing, as well as point defects associated with impurities. It is found that the lowest defect concentration is achieved after an annealing treatment at 1700°C during 24 hours. The conditions for obtaining a, «reference material» are proposed.

In order for hot-wire chemical vapor deposition to compete with the conventional plasma-enhanced chemical vapor deposition technique for the deposition of microcrystalline silicon, a number of key scientific problems should be cleared up. Among these points, the concentration of tungsten (nature of the filament), as well as the concentration of oxygen and carbon (elements issued when vacuum is broken between two runs), should not exceed threshold values, beyond which electronic properties of the films could be degraded, as in the case of monocrystalline silicon. Quantitative chemical analysis of these elements has been carried out using the secondary ion mass spectrometry technique through depth profiles. It has been shown that for a high effective filament surface area (Sf=27 cm2), the W content increases steadily from 5×1014 to 2×1018 atoms cm−3 when the filament temperature Tf increases from 1500 to 1800 °C. For a fixed Tf, the W content increases with the effective surface area Sf. Thus, considering our reactor geometry, the W content does not exceed the detection limit (5×1014 atoms cm−3) when Tf and Sf are limited to 1600 °C and 4 cm2, respectively. For O and C elements, under deposition conditions of high dilution of silane in hydrogen (96%), O and C concentrations approaching 1020 atoms cm−3 have been obtained. The introduction of an inner vessel inside the reactor, the addition of a load-lock chamber and a decrease in substrate temperature to 300 °C have led to a drastic decrease in these contents down to 3×1018 atoms cm−3, compatible with the realization of 6% efficiency HWCVD μc-Si:H solar cells.

ZnTe epilayers have been grown on (001) GaAs after depositing a Zn0.9Mn0.1Te (ZMT) buffer layer. This layer has a sphalerite structure and is (111) oriented. The (111) [112̄] ZMT direction is oriented along the (001) [110] GaAs one, with a mismatch of −6.50% for which the film lattice is in extension. Initiated by the buffer, the ZnTe film orientation is [111], instead of the [001] orientation normally observed when ZnTe is directly grown on (001) GaAs. High resolution transmission electron microscopy investigations of the microstructure of ZMT layers show twin lamellae whose width increases with distance from the interface, and dislocations with Burgers vectors parallel to the interface.

In this paper, we report on the use of in situ AsCl3 etching to suppress the indium-enriched layer formed at the InGaAs quantum well (QW) surfaces which is well known to result from In segregation mechanism. The effects of such an etching step performed at the GaAs on InGaAs QW interface have been assessed by secondary ion mass spectrometry (SIMS) and low-temperature photoluminescence spectroscopy (PL). Both SIMS and PL data clearly show that there is no degradation of the material quality. Moreover, these data are well accounted for by considering that the etching step has eliminated the In segregated layer at the InGaAs surface.

Processing of dielectric layers using a plasma-based ion implantation (PBII) technique has general implications in terms of plasma specifications and pulse characteristics. In particular, the different aspects of the processing of dielectric layers are discussed as functions of plasma density, pulse duration, and layer characteristics (thickness and permittivity). Clearly, severe limitations (true implantation energy, arcing) may appear for high-density plasmas as well as for long pulse durations when processing dielectric layers with thicknesses in the millimeter range. Typical examples of ion implantation in dielectric materials are presented, e.g. oxygen ion implantation in polymer sheets (for hydrophilic or adhesion treatments) and nitrogen implantation of polysilicon films on glass. The experimental results demonstrate the feasibility of processing dielectric layers with the PBII technique, but with severe limitations resulting from the process itself.

We report the result of investigation on hydrogen effects on GaInP/GaAs HBT structures originating from different MOCVD and CBE suppliers. It is demonstrated that hydrogen gives rise to initial unstable electrical behaviour by cross-examination of samples with and without hydrogen either intrinsically or by thermal-assisted removal. Annealing conditions to remove hydrogen have been optimized on the basis of SIMS analyses and Gummel plot characteristics to control eventual degradation of the junctions. It has been found that under particular doping and growth conditions, C2H complexes can be formed. These defects appear more stable than CH complexes which may explain the difficulty to remove hydrogen from some epitaxial layers.

Vapour-phase epitaxy of GaAs in conditions where the growth is limited by the chemical reactions of the gases with the substrate and not by gas transport is correctly understood in case the gases are produced by the decomposition of a GaAs source by H2O. Using secondary ion mass spectroscopy we have measured the efficiency at which various impurities (C, O, Si, S, Zn, Mg, Cr and Fe) are transported from the source into the grown layer. It is found that impurity transport is driven by the formation of volatile oxides, allowing to foresee which impurity can or cannot be incorporated into the grown layer. (C) 2000 Elsevier Science B.V. All rights reserved.

Two new methods are presented for the characterization of the upper (dielectrics/semiconductor) and lower (epilayer/substrate) boundary conditions for devices using planar conduction in epilayers grown on SI-GaAs substrates. They make use of the same pseudomorphic AlGaAs/InGaAs/GaAs Hall heterostructures as test devices. They are used to investigate the electronic behavior of standard cleaned and ozone cleaned epilayer/substrate interfaces, and the density of states of surface states as well as their dynamic behavior.

The study of the interdiffusion in CdTe–CdZnMgTe multiquantum wells p-type doped with nitrogen reveals that the intermixing leading to the destruction of the quantum wells occurs essentially between the Cd and Mg atoms, while the Zn atoms stay in their lattice sites. The interdiffusion is related to high density of N atoms. The n-type doping of (001) CdTe with aluminium impurities has been successfully achieved leading to very high doping levels (1.1×1019cm−3). The presence of a 2D electron gas in a CdMnTe/CdZnMgTe heterostructure modulation-doped with Al in the barrier has been demonstrated.

Gallium nitride films were grown on (0001) sapphire substrates by chemical beam epitaxy (CBE) using triethylgallium (TEGa) and ammonia (NH3) precursors. Prior to the GaN epilayer growth at 850°C, a thin GaN buffer layer was deposited at 560°C. Structural and optical properties of the epilayers were investigated as a function of the anneal treatment of the buffer layer. Annealing of the buffer in NH3 up to 900°C increases the roughness of the surface, resulting in a epilayer with higher crystallinity. Heating the buffer to 900°C results in partial desorption of the film leaving small grains on an exposed substrate. While the epitaxy on this thin buffer is two-dimensional the resulting surface consists of a hexagonal tile-structure. The level of unintentional carbon doping is high in all films, although the growth conditions need further optimization. CBE may become a promising candidate for the growth of nitride films only if the carbon incorporation is not an inherent problem of the technique.

Two new aspects of photoluminescence in GaN and alloys are presented. First, quantitative photoluminescence is carried out in a double InGaN/GaN quantum well structure. By comparing the luminescence intensities from both wells, we could extract the recombination velocities in both wells. We show that the capture is more efficient in a deeper well. Second, photoluminescence under strong excitation density is studied. Hot carrier phenomena are clearly demonstrated. From the high energy tail, we determine the electron temperature and we show that the main energy relaxation mechanism is the optical phonon emission. The effect of carrier temperature on the phonon replica on the low energy side of the luminescence peak is also emphasized.

Deuterium diffusion has been investigated in boron doped diamond as a function of the diffusion temperature and the boron concentration. The results show that, up to 480°C, hydrogen diffusion is limited by the boron concentration with a diffusion activation energy of 0.35 eV for [B] = 5×1019 cm−3. This first experimental evidence of deuterium-boron interactions in diamond is interpreted as the result of hydrogen ionization and diffusion of fairly mobile protons which form pairs with negatively charged boron acceptors.

We report on experimental evidence of hydrogen-boron interactions in boron-doped diamond from hydrogen diffusion investigations. Original deuterium diffusion studies in homoepitaxial B-doped diamond films reveal that hydrogen diffusion is limited by the B concentration with a low effective diffusion activation energy. These results are consistent with hydrogen ionization and diffusion of fairly mobile H+ that form pairs with B-. Infrared spectroscopy experiments show that boron acceptor electronic transitions are removed under hydrogenation. [S0163-1829(98)06235-3].

The kinetics of electrical activation of hydrogenated arsenic accepters in MOVPE grown cadmium telluride layers was studied for arsenic doping in the range 8 x 10(16) to 10(20) cm(-3). Thermal annealings were performed in the temperature interval 150-550 degrees C with a duration from 1 s to 1 h. The hole concentration in the annealed samples was determined by the van der Pauw method and As-H pair concentration was deduced from the intensity of the LVM absorption line at 2022 cm(-1), detected by Fourier transform spectrometry. Short annealing experiments (<1 min) showed a continuous increase in hole concentration with time and temperature, limited to about (1-2) x 10(17) cm(-3) at a temperature of 500 degrees C. The concentration of As-H pairs concurrently decreased but at a higher rate. Longer annealings usually led to a decrease in hole concentration while the As-H pair concentration either continued to drop or recovered depending on the value of arsenic doping. These results were interpreted in the framework of a theoretical analysis which took into account several processes: dissociation-recombination of impurity-hydrogen pairs, electronic ionization of arsenic impurities and electrical compensation due to the formation of arsenic-vacancy complexes. It was proposed that arsenic ionization takes place in two steps, the first one corresponding to a thermally activated conversion process and the second one to hole emission. The microscopic nature of the intermediary neutral impurity state is not known at present.

Yttrium bulk diffusion in single crystals of α-alumina is investigated by the SIMS technique, in the temperature range 1150–1500 °C. The bulk diffusion coefficients obey the relation: D(Y)(1150–1500 °C) = 1.2 10−10 exp (−295(kJ mol−1)/RT) (m2 s−1). These values are close to those of chromium diffusion in alumina, although the size of Y3+ ion is significantly higher than that of Cr3+ ion. The results are used to calculate the parameters of yttrium grain boundary diffusion in alumina, from the penetration profiles obtained in a previous work in polycrystals by the radiotracer technique.

We present an economical and non polluting vapor phase technique, allowing the growth of practically all III-V and II-VI compounds, using water as reactant. This technique will be illustrated here in the case of GaAs. We show that GaAs can be grown at very high growth rates. This has been used to obtain thick layers. We demonstrate that these layers exhibit good structural, electrical and optical properties when grown, at least, up to 5 mu m per minute. Since doping can be mastered, millimeter thick layers can be grown in a reasonable time, opening new applications for epitaxial GaAs layers such as high power electronics, nuclear detection and optics.

The improvement of a ZnTe surface layer quality is reported. For the first time a ZnTe layer of (111) orientation has been grown on (100) GaAs substrate. This orientation, which is responsible for high layer quality, was induced when adding Mn at the onset of the ZnTe growth. This leads to a ZnMnTe nucleation layer responsible for the high morphology quality of the layer.

Application of the SIMS technique to the determination of short penetration profiles in alumina provides new possibilities to study diffusion in this class of material for which the published data are limited.Impurity bulk diffusion in single crystal alumina is investigated. The results reported in this paper concern chromium, copper, silver and yttrium. The influence of atomic size, charge and polarizability on the diffusion coefficients are discussed.

Close space vapour transport is a technique that allows rapid and inexpensive epitaxial growth using water vapour as the transporting gas. The number of parameters governing the growth is small (source and substrate temperature, water vapour partial pressure) and these parameters can be varied independently. Epitaxial InP layers have been grown using this technique. The layers have been characterised by double crystal X -ray diffraction, secondary ion mass spectrometry, Hall effect, and photoluminescence. The evolution of the nature and concentration of shallow impurities and deep defects as a function of the growth parameters has been monitored. MST/3327

Trisdimethylaminoarsine (TDMAAs) has been used to clean SiO2-patterned GaAs surfaces prior to selective regrowth. Under TDMAAs pressure, the native oxide was completely removed at 480° C which is 110° C lower than the temperature of thermal oxide desorption. Compared to oxide removal with arsine, the morphology and the purity of the deoxidized surface are improved with TDMAAs cleaning. It was found that additional ex-situ chemical treatments further improve the cleaning. With the proper ex-situ preparation and TDMAAs cleaning, secondary ion mass spectrometry (SIMS) shows the removal of carbon at the regrowth interface to levels below the residual carbon concentration, while oxygen and silicon impurity concentrations are, respectively, 7.8×1011 cm-2 and 1.7×1011 cm-2. The carrier depletion at the regrowth interface is reduced to 2.6×1011 cm-2 and contact resistivity is lowered to 2.7×10-6 Ω· cm2.