The influence of the scatter of heat flux at the m/c interface on the frequency of appearance of poly body and twin defects during 6″ semi-insulating GaAs crystal growth by the VGF method (original) (raw)
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Optimization of VGF-growth of GaAs crystals by the aid of numerical modelling
Journal of Crystal Growth, 2002
The VGF growth of Si-doped GaAs crystals is improved considerably by optimizing the design of the crucible support and the temperature profile during the growth run. Inverse simulation with the software program CrysVUN++ was used for this procedure. The criteria for the optimized conditions are flat phase boundaries and low thermal stress during the whole growth run. The crystals which were grown according to the simulated conditions indeed showed flat phase boundaries and a very low EPD (o100 cm À2 ) within the whole crystal. It is shown that the growth conditions in the seed well and conical part of the crystal have a major influence on the dislocation density in the whole crystal. r (G. M . uller). 0022-0248/02/$ -see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 -0 2 4 8 ( 0 1 ) 0 2 3 2 4 -7 G. M . uller, B.
Journal of Crystal Growth, 1999
GaAs single crystals (silicon-doped, 2 inch) with extremely low dislocation densities (etch pit density (EPD) 50-1000 cm\) were grown by the vertical gradient freeze method. In these crystals we characterised different types of dislocations by the aid of white beam X-ray diffraction topography and infrared transmission microscopy. It was found for decreasing dislocation densities (EPD(200 cm\), that dislocations having a line vector l, which is parallel to the [0 0 1] growth direction of the crystals, become more and more dominant. These residual dislocations are induced by the seeding process (so far we were using LEC-grown seed crystals). These residual dislocations cannot be avoided by minimising the thermal stress during the crystal growth process.
Applied Physics A Solids and Surfaces, 1988
There is a diffraction-induced phase effect in the RHEED intensity oscillation technique used in MBE, whereby intensity maxima only correspond to monolayer completion for very restricted conditions. In particular, the angle of incidence of the primary beam is extremely critical. The effect occurs because the total intensity at the measured position of the specular beam is always derived from at least two different diffraction processes, which do not have the same phase relation to monolayer formation. It can be accomodated either by a systematic series of measurements to establish an empirical relationship between incidence angle and phase, or by Fourier transform techniques. Unless full account is taken of this purely diffraction-induced effect, very misleading results can be obtained for the time constants of the recovery period following cessation of growth and this is illustrated for GaAs. The effect also has important implications for the growth-interrupt technique. In addition, it is shown that for heterojunction formation in the GaAs/(A1, Ga)As system, adatom (Ga and A1) migration lengths are of greater importance than the position in the monolayer at which the composition is changed, and that RHEED can provide only limited information on the interface structure.
Surface morphology of low temperature grown GaAs on singular and vicinal substrates
Materials Science and Engineering: B, 2002
The evolution of the surface morphology of epitaxial GaAs layers grown at low substrate temperatures (LT-GaAs) on singular and vicinal (001) GaAs substrates is studied by means of kinetic Monte-Carlo simulations. The simulation model includes the effects of Ehrlich-Schwoebel barriers at step-edges as well as anisotropic surface diffusion. We find that the surface morphology is dominated by a pattern of elongated growth mounds, which are organized into columns parallel to [1(10]. The formation of this pattern is gradually suppressed on vicinal substrates as the misorientation angle increases. Simulated surface morphologies are compared to atomic force microscopy measurements on LT-GaAs epilayers grown on singular GaAs(001) substrates at different temperatures and good quantitative agreement is found. We propose to use vicinal substrates for LT-GaAs growth in order to overcome the known problem of epitaxial breakdown above a certain epitaxial thickness.
Microstructure of annealed low-temperature-grown GaAs layers
Applied Physics A Solids and Surfaces, 1991
The crystal structure and orientation of As precipitates in annealed low-temperature GaAs (LT-GaAs) layers have been investigated by transmission electron microscopy. Three types of As precipitates were identified in layers grown by molecular beam epitaxy at substrate temperatures from 180 ° to 210 ° C. In the monocrystalline LT-GaAs layers small "pseudocubic" As precipitates (2-3 nm diameter) coherent with the GaAs lattice were observed. These precipitates lose their coherency when a certain critical size is exceeded. Precipitates of similar sizes are occasionally found for which a TEM lattice image cannot be obtained. These precipitates are believed to be amorphous. Larger As precipitates with a hexagonal structure (>4 nm diameter) were also found in the layers. These hexagonal As precipitates were observed to be largest near structural defects. The effect of these precipitates on the structure and on the electronic properties of the host GaAs is discussed.
Effect of the starting surface on the morphology of MBE-grown GaAs
Materials Science and Engineering: B, 2000
In this paper, we study the homoepitaxial growth of GaAs by molecular beam epitaxy on substrates that have different pre-growth roughness due to the method of removing the native oxide. The evolution of the surface roughness of 1 mm thick GaAs films grown at 553°C was monitored in real time using ultraviolet light scattering, and compared with ex situ atomic force microscopy measurements of the power spectral density (PSD) of the surface morphology. The PSD at a spatial frequency of 2 mm − 1 , is approximately three orders of magnitude larger for films grown on thermally cleaned substrates than for films grown on substrates cleaned with atomic hydrogen. No mounding indicative of unstable growth was observed in the films cleaned with atomic hydrogen.
Photothermal deflection spectroscopy study of defects in semi-insulating GaAs
Applied Physics A Solids and Surfaces, 1991
Subgab absorption measurements carried out by photothermal deflection spectroscopy in semi-insulating GaAs are used to study the concentration of defects found in as-grown and in heat treated material. Measurements carried out in ion-implanted and furnace-annealed samples prove to be a useful tool for monitoring the successful recovery of the ion implantation damage.
Effects of incident UV light on the surface morphology of MBE grown GaAs
Journal of Crystal Growth, 2015
Light-assisted molecular beam epitaxy is a promising technique for improving the growth of metastable semiconductor alloys traditionally grown at low temperatures. The effect of photon irradiation on adatom incorporation dynamics is studied for GaAs homoepitaxy on vicinal surfaces. Irradiation is found to increase the temperature at which the growth mode transitions from layer-by-layer island nucleation to step flow growth and to alter the surface morphology. These surprising changes are discussed in the context of modification of adatom diffusion and incorporation processes.