Effects of SiO2 overlayer at initial growth stage of epitaxial Y2O3 film growth

We investigated the dependence of the Y₂O₃ film growth on Si surface at initial growth stage. The reflection high-energy electron diffraction, X-ray scattering, and atomic force microscopy showed that the film crystallinity and morphology strongly depended on whether Si surface contained O or not. In particular, the films grown on oxidized surfaces revealed significant improvement in crystallinity and surface smoothness. A well-ordered atomic structure of Y₂O₃ film was formed on 1.5 nm thick SiO₂ layer with the surface and interfacial roughness markedly enhanced, compared with the film grown on the clean Si surfaces. The epitaxial film on the oxidized Si surface exhibited extremely small mosaic structures at interface, while the film on the clean Si surface displayed an island-like growth with large mosaic structures. The nucleation sites for Y₂O₃ were provided by the reaction between SiO₂ and Y at the initial growth stage. The SiO₂ layer known to hinder crystal growth is found to enhance the nucleation of Y₂O₃, and provides a stable buffer layer against the silicide formation. Thus, the formation of the initial SiO₂ layer is the key to the high-quality epitaxial growth of Y₂O₃ on Si.     

Solid phase epitaxial growth of Si through Al film

Uniform epitaxial growth has been obtained by dissolution and transport of an evaporated Si film through an evaporated Al film at temperatures below 500°C. By analyzing the samples made in different ways we show that the presence of a cap on the metal layer, which inhibits the diffusion of the metal through the evaporated Si, plays a fundamental role. The cap consists of a thin oxide layer grown on top of the metal. The cap is made by leaving the sample in vacuum for two days or by heating the sample in vacuum before the Si deposition. The study of the initial growth rate on 〈100〉 and 〈111〉Si substrates reveals that the growth starts as islands which grow until they coalesce to form a continuous layer. Different growth rates have been obtained by using 〈100〉 and 〈111〉Si substrates. Typical growth rates are 50 Å/min at 330°C on 〈100〉 and 100 Å/min at 392°C on 〈111〉. The activation energy of the process is 1.2 eV.     

Hydrodynamic description of epitaxial film growth in a horizontal reactor

Growth rate uniformity of epitaxial films is an important prerequisite for fabricating semiconductor devices. The correlation between the film thickness distributions and the vorticity distributions in the flow field is investigated in detail. Equations for conservation of mass, momentum and energy are solved numerically. The vorticity around the substrates and the vorticity gradient on the substrates are calculated from the velocity distribution rather than by solving the species equations. The substrate temperature is 1000 K, the total pressures are 2 and 20 Torr and the Reynolds numbers are 1, 10 and 100. The thicknesses of the films deposited by low-pressure chemical vapor deposition are measured. As a result, it can be shown that the deposited film thickness distributions agree with the vorticity gradient distributions. This suggests that vorticity has an important influence on film deposition.     

Isothermal liquid phase epitaxy of A 3 B 5 compounds under excessive vapor pressure of the B 5 component

A mathematical model has been developed of isothermal epitaxial growth of A³B⁵ films on the A³B⁵ substrates from flux by creating the excessive pressure of diatomic vapors of the B ⁵ component. The model is based on the diffusion equation with the nonlinear boundary condition at the evaporation surface and the thirdkind condition at the crystallization surface. The problem is solved numerically on a computer.     

Solid-phase epitaxy for the formation of superlattices based on A3B5 compounds

To form superlattices based on A³B⁵ compounds, it is suggested to use solid-phase epitaxy (SPE) which includes recystallization of super-thin films of stoichiometric composition deposited by laser evaporation on single-crystal plates or films with the same or close composition. The recrystallization temperature is shown to be reduced considerably for the film grains with its curvature differing significantly from zero and which are in contact with their own single-crystal seed having practically zero curvature. The single-crystal multilayer films GaAs-(Al, Ga)As … GaAs were formed at 300°C. The recrystallization rate at this temperature was 40 Å/min. The autocatalytic action of the single-crystal seed strongly reduced the activation energy of the SPE process, which may be due to diffusion in solid phase.     

Study of film crystallization kinetics initial stage by Monte Carlo simulation

The Monte Carlo Simulation has been used for studying the initial stage characteristics of film crystallization during the layer-by-layer film growth by two-dimensional nucleation. It is shown that the non-monotonous changes of the growing film perimeter and mass correspond to the reflection intensity oscillation from the growth surface. The observed changes of the overgrowing part of the surface are in agreement with the probability-statistical calculations. The vizualization of surface relief changes during the growth process under different conditions has been provided.     

Electron microscopy of epitaxial structures of pseudobinary A III B V solid solutions and the model of nonequilibrium ordering in epitaxial growth

The results of the electron microscopy studies of self-modulated GaAlAs, GaAsP, and InGaP layers have been generalized, and the laws governing the self-oscillatory growth of these materials have been formulated. The growth characteristics under the autocatalysis conditions were established from a computer simulation of the epitaxial process. It is demonstrated that the autocatalytic model of crystallization corresponds to the experimental characteristics of self-modulation. The anomalies in electron microscopy images of the boundaries were revealed, which can be interpreted only with the invocation of the autocatalytic model. The reliabilities of various theoretical self-modulation models are also discussed.     

Initial stage of growth of the GD a-Si:H

The time dependences of the optical emission intensities of SiH,H and He lines and also of the gas temperature have been studied. It is demonstrated that 10–100 sec are necessary for full stabilization of plasma. This can explain the different properties of the initial 30–300 Å layer of a-Si:H.     

Modification of the mass weighing in A3B5 automated Czochralski crystal growth techniques

Modification of weight signal of LEC, VCZ crystal growth processes based on the knowledge of the weight signal in the past during the pulling process was considered. This modification is necessary for development and improvement of the direct automated weight control in these techniques of crystal growth. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optically monitoring and controlling epitaxial growth

We provide a perspective on current capabilities for optically monitoring and controlling epitaxial growth, and discuss examples taken from recent work at Bellcore.     

Investigation of preparation and properties of epitaxial growth GaN film on Si(1 1 1) substrate

In this paper, a single crystalline GaN grown on Si(1 1 1) is reported using a GaN buffer layer by a simple vacuum reactive evaporation method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence measurement (PL), and Hall measurement results indicate that the single crystalline wurtzite GaN was successfully grown on the Si(1 1 1) substrate. The surface of the GaN films is flat and crack-free. A pronounced GaN(0 0 0 2) peak appears in the XRD pattern. The full-width at half-maximum (FWHM) of the double-crystal X-ray rocking curve (DCXRC) for (0 0 0 2) diffraction from the GaN epilayer is 30 arcmin. The PL spectrum shows that the GaN epilayer emits light at the wavelength of 365 nm with an FWHM of 8 nm (74.6 meV). Unintentionally doped films were n-type with a carrier concentration of 1.76×10¹⁸/cm³ and an electron mobility of 142 cm³/V s. The growth technique described was simple but very powerful for growing single crystalline GaN films on Si substrate.     

Bulk and epitaxial growth of silicon carbide

Silicon carbide (SiC) is a wide bandgap semiconductor having high critical electric field strength, making it especially attractive for high-power and high-temperature devices. Recent development of SiC devices relies on rapid progress in bulk and epitaxial growth technology of high-quality SiC crystals. At present, the standard technique for SiC bulk growth is the seeded sublimation method. In spite of difficulties in the growth at very high temperature above 2300 °C, 150-mm-diameter SiC wafers are currently produced. Through extensive growth simulation studies and minimizing thermal stress during sublimation growth, the dislocation density of SiC wafers has been reduced to 3000–5000 cm⁻² or lower. Homoepitaxial growth of SiC by chemical vapor deposition has shown remarkable progress, with polytype replication and wide range control of doping densities (10¹⁴–10¹⁹ cm⁻³) in both n- and p-type materials, which was achieved using step-flow growth and controlling the C/Si ratio, respectively. Types and structures of major extended and point defects in SiC epitaxial layers have been investigated, and basic phenomena of defect generation and reduction during SiC epitaxy have been clarified. In this paper, the fundamental aspects and technological developments involved in SiC bulk and homoepitaxial growth are reviewed.     

Growth kinetics,structure and surface morphology of AlN/α-Al2O3 epitaxial layers

The gas-phase epitaxy of AlN on saphire substrates in the system Al HCl NH₃–Ar was investigated. The uniformity and structural perfection of the layers were shown to be determined by gas dynamics in the growth zone. The growth rate of AlN-layer is proportional to AlCl concentration in the growth zone and does not depend on NH₃ partial pressure. This is in accordance with the law of diffusional stoichiometry. The morphology of AlN-layers was shown to be dependent on the growth rate and the substrate orientation. Smooth mirror-like layers were prepared on the sapphire planes (0001) and (1120) at low growth rates. X-ray microanalysis showed the oxygen impurity content at the level 1 — 5 · 10²¹ cm⁻³. Other impurities were not available.     

Electron microscope study of intrinsic and extrinsic stacking faults,and twins in SOS at the early stage of epitaxial growth

Fine structures of the Si films on (1$\text{1}$02) sapphire have been studied by a lattice resolution TEM. The Si was deposited by the pyrolysis of silane in H₂ at 1000°C at a growth rate of 0.1μm/min. The samples for TEM were prepared by peeling off the Si films from the substrates after HF treatment. A film having a mean thickness of 500 Å was composed of (100) and {110} domains. The volume fraction of the {110} domains was more than 50% and about constant as a function of growth time. The {110} domains contained much higher density of microtwins than the (100) domains. These microtwins had various thicknesses including one atomic layer (intrinsic stacking faults) and two atomic layers (extrinsic stacking faults). The density of the intrinsic stacking faults was higher than those of extrinsic stacking faults and other twins. The {110} and (100) islands were nucleated independently and the microtwins were also present in the islands smaller than 500 Å in diameter.     

Vapour-phase epitaxial growth of ZnS on GaP

Single crystal layers of ZnS about 100 μm thick were grown epitaxially on GaP substrates in an open tube system using source ZnS powder and a flowing hydrogen atmosphere. The growth rate for different substrate temperatures increases with increasing hydrogen flow rate, but the growth rate profiles resemble each other in shape. The profile shifts towards the low temperature side as the source temperature is decreased. The (111)B substrate orientation is found to be preferable to the (111)A or the (100) with respect to surface morphology and crystal quality. X-ray diffraction investigations and luminescent properties show that the (111)B grown layers are of high quality. All ZnS layers grown on GaP substrates are craked on cooling, which may be due to the thermal expansion mismatch between the layer and the substrate. Heat-treatment of the grown layer does not reduce the resistivity, but increases the photoluminescence intensity markedly. Selective vapour-phase epitaxial growth has been successfully applied resulting in crack-free ZnS layers on GaP substrates.     

Optimized growth conditions of GaN epitaxial layers

Optimized growth conditions of the epitaxial GaN layers on the (0001) oriented sapphire substrates in the Ga/HCl/NH₃/H₂ system have been proposed. The corresponding growth rate varied about the value 0.5 μm · min⁻¹. The study of surface morphology and X-ray diffraction have confirmed the single crystalline character of the layers even though the surface shows a faceted structure. The c/a ratio calculated from our measured data of the lattice parameters was found 1.624 which is relatively close to the ideal close-packed wurtzite structure value. The cathodoluminescent spectra of the layers with a sufficient thickness were characterized by a peak at 3.35 eV having a halfwidth of about 0.2 eV.     

Studies on epitaxial growth of organic compounds on sucrose by the fourier transform method (I). On crystal growth of the participants

Epitaxial growth of organic compounds on sucrose crystals has been observed. In any case two-dimensional lattice analogies exist. The structural relations are, as a rule, unknown. In the present first part crystal growth of the participants was investigated. Equilibrium and growth forms of host (sucrose) and guest crystals (β-succinic acid, hexachlorobenzene, anthraquinone, isatin) have been determined by the Fourier transform method. The growth polyhedra fully correspond to the experimental observations.     

Macrosteps dynamics and the growth of crystals and epitaxial layers

Step pattern stability of the vicinal surfaces during growth was analyzed using various surface kinetics models. It was shown that standard analysis of the vicinal surfaces provides no indication on the possible step coalescence and therefore could not be used to elucidate macrostep creation during growth. A scenario of the instability, leading go macrostep creation, was based on the dynamics of the step train, i.e. the step structure consisting of the high (train) and low (inter-train) density of the steps. The critical is step motion at the rear of the train which potentially leads to the step coalescence i.e. creation of the double and multiple step. The result of the analysis shows that the decisive factor for the step coalescence is the step density ratio in and out of the train. The ratio lower than 2 prevents double step formation irrespective of the kinetics. For higher ratio the coalesce depends on step kinetics: fast incorporation from lower terrace stabilizes the single steps, fast incorporation from upper leads to step coalescence. The double step is slower than the single steps, so the single steps behind catch up creating multistep and finally macrostep structure. The final surface structure consists of the macrosteps and superterraces, i.e. relatively flat vicinal segments. The macrostep alimentation from lower superterrace leads to emission of the single steps which move forward. Thus the single step motion is dominant crystal growth mode in the presence of the macrosteps. These steps finally are absorbed by the next macrostep. The absorption and emission of single steps sustain the macrostep existence, i.e. the macrostep fate is determined the single step dynamics. The condition for single step emission was derived. In addition, the macrosteps are prone to creation of the overhangs which results from surface dynamics coupling to impingement from the mother phase. The angular preferential access of the bulk material to the macrostep edge, leads to the overhang instability and creation of inclusions and dislocations.