Laurent Auvray

Large Area DPB Free (111) β-SiC Thick Layer Grown on (0001) α-SiC Nominal Surfaces by the CF-PVT Method

Thick (111) oriented β-SiC layers have been grown by hetero-epitaxy on a (0001) a-SiC substrate with the Continuous Feed-Physical Vapour Transport (CF-PVT) method. The growth rate was 68 µm/h at a pressure of 2 torr and a temperature of 1950°C. The nucleation step of the β-SiC layer during the heating up of the process was studied in order to manage first the a to b heteropolytypic transition and second the selection of the b-SiC orientation. With a adapted seeding stage, we grew a 0.4mm thick layer almost free of Double Positioning Boundaries on a 30mm diameter sample. First observations of the layer by cross-polarised optical Microscopy are presented both in planar view and in cross section geometry.

AFM study and optical properties of GaAsN/GaAs epilayers grown by MOVPE

Abstract We report a study on surface morphology and optical properties of GaAsN epilayers grown on GaAs (1xa00xa00) vicinal substrates by metalorganic vapor-phase epitaxy (MOVPE), using dimethylhydrazine as the N source. The surface morphology was investigated by atomic force microscopy (AFM) as a function of N composition and growth temperature ( T g ). At T g =530–550°C, we observed a transition from a bunched step/terrace structure towards a surface with indistinct step/terrace structure when increasing the N content. We attribute this evolution to a transition from step-bunching towards 2D-nucleation growth, related to decreased Ga surface-diffusion length. The optical properties were studied using room-temperature (RT) and low-temperature photoluminescence (PL), and photoreflectance (PR). Post-growth thermal annealing were carried out on GaAs-capped layers. A drastic increase of the RT PL intensity and a narrowing of the linewidth were observed under optimum annealing conditions. The influence of annealing temperature and duration were also examined.

Analysis of nitrogen incorporation mechanisms in GaAs1-xNx/GaAs epilayers grown by MOVPE

Abstract The incorporation of nitrogen in Ga(As,N)/GaAs grown by metalorganic vapor phase epitaxy has been investigated as a function of growth conditions. The evolution of the solid composition was studied as a function of growth temperature between 500 and 600°C, and gas-phase composition. For instance, at growth temperatures of 510–560°C, the solid composition varies slowly with T , with an apparent activation energy of 0.6 eV. For T >560°C, an exponential decrease is dominantly observed with an apparent much higher activation energy of 3.7 eV. The effect of the growth temperature is analyzed, taking account for the different surface reaction mechanisms. The observed transition between the two regimes is attributed to an increased desorption of nitrogen at high temperatures. In light of experimental results, we propose a surface kinetics model based on the competitive adsorption of group V precursors. We also deduced an energy barrier for adsorption of group V species.

Micropipe-induced birefringence in 6H silicon carbide

The micropipe-induced birefringence of 6H silicon carbide (SiC) is measured and quantitatively modelled. A good agreement can be obtained between theory and experiment, provided that background residual stress is added to the local dislocation-induced stress. Observations are compatible with or predictable from the Burgers vector values, and birefringence is shown to be an interesting tool for probing the nature of the dislocations associated with e. g. micropipes; it is also faster than and complementary to the more involved techniques of transmission electron microscopy or X-ray topography.

Electron Back Scattering Diffraction (EBSD) as a Tool for the Investigation of 3C-SiC Nucleation and Growth on 6H or 4H

In this paper, we present the use of Electron Back Scattering Diffraction (EBSD) as a tool for the investigation and monitoring of 3C-SiC (β) nucleation and growth on 6Hor 4H-SiC (α) (0001) nominal surfaces. Experiments were performed under silicon rich gas phase, for temperatures varying from 1900 to 2100 °C and different supersaturations. For each condition, phase and orientation maps are imaged from the EBSD technique. Results are presented in terms of α-SiC/β-SiC ratios and β(1)/β(2) ratios where β(1) and β(2) are related to the two possible orientations for the 3C-SiC to epitaxially grow on the 4H-SiC (0001) nominal surface. We demonstrate that, depending on the experimental conditions, it is possible to control first the formation of 3C rather than 4H-SiC and to control a 3C orientation rather than the other and thus to limit the DPB density.

Buried Selective Growth of p-Doped SiC by VLS Epitaxy

Selective epitaxial growth in buried patterns was studied using the vapour-liquid-solid mechanism in Al-Si melt in order to obtain p+-doped SiC localized layers on 4H-SiC substrate. Homogeneous deposition with step bunched morphology was obtained by adding propane at room temperature before growth at 1100°C. Patterns as large as 800 µm and as narrow as 10 µm were completely filled in this way. The deposition kinetics demonstrates that the process is self limited and mainly depends on the initial amount of Si in the liquid. The deposit is highly p-type doped and the p-n junction is demonstrated.

MOVPE growth of GaAsN: surface study by AFM and optical properties

Abstract We report on the growth of GaAs1−xNx thin films on GaAs substrates (2° off) by metalorganic vapor-phase epitaxy, in the temperature range 500–600°C. A mixture of N2 and H2 was used as the carrier gas. Using dimethylhydrazine as nitrogen source, we incorporated up to 3.5% of nitrogen, at 530°C. The growth condition dependence of nitrogen content was studied, and it reveals a distribution coefficient 350 times lower for nitrogen than for arsine at 530°C. Nitrogen incorporation is controlled by surface kinetics. The evolution of surface morphology has been investigated by atomic force microscopy as a function of the nitrogen composition and of growth temperature. For nitrogen content up to ∼2%, the GaAsN vicinal surface is characterized by a step–terrace structure with bunched steps, and the step edges straighten when increasing the growth temperature. For higher nitrogen content terraces are no longer observed and, above ∼3%, widely-spaced cross-hatch lines, characteristic of a partial relaxation of strain in the epilayers, appear. Optical properties were studied by low (7xa0K) and room-temperature photoluminescence and photoreflectance. As usual for this material, a degradation of optical characteristics is observed with increasing N content along with the evolution of surface morphology.

Strain-induced surface morphology of slightly mismatched InxGa1−xAs films grown on vicinal (100) InP substrates

A surface investigation by atomic force microscope of InP and slightly lattice-mismatched InGaAs epilayers grown by metalorganic vapor phase epitaxy shows the effect of strain on InGaAs/InP surface morphology. Epilayers were grown at 600u200a°C with arsine at 760 Torr. We could clearly observe the regular step/terrace-like feature of the vicinal surface morphology for InP and InGaAs lattice-matched epilayers. It is shown that the step flow mode appears with a step edge with regular spacing for lattice-matched epilayers. A crosshatch pattern, i.e., an array of perpendicular lines visible at the surface, were obtained for strain-relaxed InGaAs epilayers (|(Δa/a)⊥|>10−3) with an average separation of 1000–1500 nm. The detailed surface structure of the step edge presents a specific bending of terraces. The influence of step kinetics on the morphological stability of the surface will be illustrated. The relationship between the misfit dislocation network and anisotropic growth rate of the front step will be discussed.

Photoluminescence properties and high resolution x-ray diffraction investigation of BInGaAs/GaAs grown by the metalorganic vapour phase epitaxy method

In this paper, we report the obtention of quaternary (B)InGaAs/GaAs alloys grown by metal organic vapour phase epitaxy has been studied using high resolution x ray diffraction (HRXRD) and photoluminescence (PL) measurements. HRXRD has been achieved to determine the indium fraction (35%) incorporated into BGaAs, which shows that the strain effects have been reduced compared to the InGaAs one. Through further careful inspection, boron-indium gallium arsenic (BInGaAs) epilayer exhibits several PL peak emissions. They are associated to the exciton bond induced by the boron isoelectronic and cluster defect states. In contrast, for the BInGaAs single quantum well (SQW), we have a band to band transition mainly influenced by the confinement of electron-hole pairs in the BInGaAs well. However, the PL of BInGaAs SQW temperature-dependence has shown a localization effect due to the conduction-band modulation induced by the boron clustering in the structure. At high PL temperature, we have a band to band transition ...

Characterization of Thick 2-Inch 4H-SiC Layers Grown by the Continuous Feed-Physical Vapor Transport Method

We present the first investigation of 2 inch diameter 0.5 mm thick 4H-SiC layers grown by the CF-PVT (Continuous Feed-Physical Vapor Transport) method. From Synchrotron White Beam X-Ray Topography we show that no new defect is generated in the CF-PVT material with respect to the 4H-SiC seed. We also show that a large strain takes place at the layer to seed interface which probably comes from the difference in doping level and thus in lattice parameter between the layer and the seed. From Raman experiments we demonstrate a high structural uniformity and low residual doping level. This is a surprising result which comes despite the lack of sophisticated purification procedure. To get confirmation, we have performed SIMS and LTPL investigations.