Composition Of Epitaxial Layers Research Articles

Formation of epitaxial 3C-SiC layers on Si by rapid vacuum thermal processing

The results of a study of the structure and phase composition of epitaxial layers of silicon carbide (SiC) formed on silicon substrate with orientation (100) under rapid vacuum thermal processing are presented. Planar-view transmission electron microscopy investigation revealed the formation of epitaxial layers of cubic polytype SiC (3C-SiC) on silicon in the process of carbidisation at 1100 °C during 30 s, using a gas mixture of propane (10 %) and argon (90 %) as a carbon source. The formation of a monocrystalline 3C-SiC with polycrystalline inclusions and twins on all possible planes {111} was found. A rather narrow band of 793 cm–1 transverse optical phonon mode SiC on Raman spectra confirms the formation of a cubic polytype SiC. It is noted that the presence of a 180 cm–1 spectral line and a 793 cm–1 half-width band on Raman spectra indicate the presence of deformation defects in SiC.

Self-Organization of the Composition of AlxGa1 – xN Films Grown on Hybrid SiC/Si Substrates

The phenomenon of self-organized change in the composition of epitaxial layers of the AlxGa1 ‒ xN solid solution during their growth by chloride-hydride epitaxy on SiC/Si(111) hybrid substrates is discovered using spectral ellipsometry, Raman spectroscopy, and scanning microscopy with an X-ray spectrometer. It is found that interlayers or domains consisting of AlGaN of stoichiometric composition appear during the growth of AlxGa1 – xN layers with a low (about 11–24%) content of Al. A qualitative model is proposed, according to which self-organization in composition occurs due to the effect of two processes on the growth kinetics of the AlxGa1 – xN film. The first process is associated with the competition of two chemical reactions proceeding at different rates. One of these reactions is the formation of AlN; the second reaction is the formation of GaN. The second process, closely related to the first one, is the appearance of elastic compressive and tensile stresses during the growth of AlxGa1 – xN films on SiC/Si(111). Both processes influence each other, which leads to a complex pattern of aperiodic variation of the composition over the thickness of the film layer.

Influence of substrate conductivity type on the thickness and composition of epitaxial layers grown by Liquid Phase Epitaxy

It is shown that the conductivity of the substrate has a non negligible effect on the thickness and composition of epitaxial layers grown by Liquid Phase Epitaxy. The growth experiments have been done on the systems GaAs/GaAs, GaAlSb/GaSb and GaInAsSb/GaSb. To insure strictly the same growth conditions the growth was done simultaneously, from the same liquid phase, on the different substrates.

Metal-organic vapour phase epitaxy of BInGaN quaternary alloys and characterization of boron content

BInGaN quaternary alloys with up to 2% boron and 14% of indium have been grown on GaN/sapphire template substrates by metal-organic vapour phase epitaxy (MOVPE). Epitaxial layer composition was determined by secondary ion mass spectroscopy (SIMS), and confirmed by X-ray photoelectron spectroscopy (XPS). Bandgap energies were measured using optical transmission and reflection spectroscopy. We find that boron incorporation in BInGaN reduces the bandgap, causing an effect similar to the increase of indium content in InGaN. However, adding boron has the advantage of decreasing the lattice mismatch with conventional GaN substrates.

Transmission Electron Microscopy and Luminescence Studies of Quantum Well Structures Resulting from Stacking Fault Formation in 4H-SiC Layers

The formation of 3C-SiC staking fault inclusions in higher band-gap other SiC polytypes provides a unique possibility to obtain quantum well (QW) structures without changing of chemical composition of epitaxial layers during growth. [1] In this report we present low temperature microphotoluminescence and transmission electron microscopy (TEM) studies of 3C-SiC stacking faults inclusions in 4H-SiC homoepitaxial layers, grown by molecular vapor deposition (MOCVD) on 4H-SiC substrates with an 8o surface miscut from the basal plane. TEM investigations showed that basal plane inclusion with cubic 3CSiC stacking faults present in the substrate propagate into the 4H-SiC layer material, forming inclined QW structures. The distance between SF was found to vary from 2 nm to 1.5 μm depending on the position on the layer. The presence of SF in the layer was confirmed by photoluminescence studies. They showed that in addition to excitonic emission typical for high quality 4H-SiC layers, well defined group of several emission lines around energy of 2.9 eV, which we attribute to QW formation induced by 3C-SiC staking faults [2]. In contrary to the emission due to nitrogen-bound excitons (observed at higher energy), which remains practically unchanged when changing position on the sample, the energy of spectral lines related to SF emission shows quasi-periodic jumps between well defined values when scanning on the sample surface (laser spot on the sample is of about 1-2 μm). The observed intensity pattern changes in a similar way. The obtained experimental data are discussed in terms of single, double and multiple quantum wells formed form neighboring 3C-SiC SF layers. It is confirmed that a concept of “structure-only” QW is promising from the point of view applications, provided precise control of FS formation during the growth of SiC based nanostructures is attainable. Our results show that, at least the formation of SF related QW structures can be successfully initiated by appropriate substrate preparation.

Room temperature continuous wave operation of a surface-emitting two-dimensional photonic crystal diode laser

We achieved room temperature continuous wave operation of a surface-emitting two-dimensional photonic crystal diode laser by current injection. This is the first time ever that room temperature continuous wave operation of a photonic crystal diode laser has been realized. This laser features single mode oscillation over a large area, which is impossible for conventional lasers. In this work, we optimized the epitaxial layer composition for better carrier confinement and clarified the relationship between the diameter of the air holes in the photonic crystal and the threshold current of the laser in order to estimate the optimized threshold current.

Effect of the composition of the solid solution on the high-temperature microhardness of SiGe heteroepitaxial layers grown on Ge and Si substrates

The effect of the composition of epitaxial layers (ELs) of the SixGe1−x solid solution grown on Ge and Si substrates on their microhardness and the length of dislocation rosettes forming around indentations is studied at a homologous temperature 0.5Tmelt for each composition. For the SixGe1−x/Ge (0≤x<0.15) and SixGe1−x/Si (0.85<x≤1) ELs, the dependences of the microhardness and the length of dislocation rosettes on the solid-solution composition are nonmonotonic. The nonmonotonic change in the plasticity of the ELs is most likely caused by hardening of the solid solutions in a certain composition range due to their spinodal decomposition with the formation of clusters and disperse precipitates.

Comparative study of RBS, SIMS and VASE for characterisation of high electron mobility transistors

The investigated devices consist of InGaAs/InAlAs multilayer films grown by molecular beam epitaxy on InP. Results from two samples with the same epitaxial layer composition but with different layer thicknesses are presented. Of the three techniques investigated, Rutherford backscattering spectrometry (RBS), variable angle spectroscopic ellipsometry (VASE) and secondary ion mass spectrometry (SIMS), VASE appears to be the choice for routine work. Both RBS and SIMS are shown to be valuable complementary techniques.

Vapor-phase epitaxy of InxGa1−xN using chloride sources

The growth kinetics of InxGa1−xN epitaxial layer on GaN-buffer/sapphire (0001) substrate and the vapor–solid distribution relationship of the chloride source system are investigated. The growth rate decreases with increasing growth temperature. The solid composition of epitaxial layers becomes more GaN-rich with the increasing growth temperature and is very sensitive to the H2 mole reaction in the carrier gas. In the vapor–solid distribution relationship, the preferential incorporation of the GaN component is observed. The indium droplets are not observed on the surface of InxGa1−xN films in the entire composition range. Without In droplets formation, the In-rich InxGa1−xN alloys as high as 0.8 of In content are obtained.

Closed-Loop Control of MBE Using an Integrated Multi-Sensor System

ABSTRACTThe use of in situ sensors to achieve real-time control of molecular beam epitaxy (MBE) is a rapidly evolving technology that promises to revolutionize MBE in terms of process repeatability and first-pass success, and consequently to improve the overall yield and reduce the cost of the process. To achieve robust real-time control of MBE, we have constructed a multiple-sensor control system comprising in situ sensors for substrate temperature, for effusion cell fluxes, and for the epitaxial layer composition and thickness, along with advanced software to manage the sensor information and execute sensor-feedback control algorithms. This system has been used to grow a number of different III-V semiconductor materials and device structures, including heterojunction bipolar transistors, resonant tunneling devices, and mid-IR lasers. In the present paper, we present results demonstrating control and regulation of substrate temperature and epitaxial layer composition during the growth of lattice-matched InGaAs and InA1As on InP. The control algorithms and software used in the system are described, and we discuss how the synergistic application of multiple sensors allows the regime of composition control to be expanded beyond what would be possible with only a single composition sensor.

Patterned self-assembly of one-dimensional arsenic particle arrays in GaAs by controlled precipitation

A process for the patterned self-assembly of nanometer-scale particles within a solid is described. The process uses crystal strain and composition to guide the formation of arsenic precipitates in GaAs-based epitaxial layers grown at low temperature by molecular beam epitaxy. The lateral particle position is controlled by the strain produced by a surface stress structure while the vertical position is controlled by the epitaxial layer composition. Arsenic particles ∼16-nm in diameter are fabricated in one-dimensional arrays with a 23-nm edge-to-edge particle spacing at a depth of 45 nm below stressors 200 nm in width, thereby demonstrating this technique.

Mg-doping transients during metalorgic vapor phase epitaxy of GaAs and AlGaInP

We studied magnesium-doping transients during metalorgic vapor phase epitaxy of GaAs and (Al x Ga 1- x ) 0.5 In 0.5P (0 ⪯ x ⪯ 0.7). We examined the transient of Mg concentration depth profile through epitaxial layers when Mg precursors are initially injected into the reactor (doping delay). We found that increasing the Al composition of epitaxial layers, i.e., increasing the mole fraction of Al precursors in the reactor, significantly reduces the Mg-doping delay. We obtained this result for both trimethylaluminum (TMAl) and triethylaluminum (TEAl). We quantitatively modeled this phenomenon based on the competitive adsorption of Mg and Al precursors on the internal surface of the reactor. Our model also explains that the Mg concentration in epitaxial layers increases either linearly or superlinearly with the Mg precursor input, depending on the length of the doping delay.

Microstructure and luminescence properties of Ga x In 1- x P/GaAs heterostructure

The GaxIn1-xP/GaAs heterostructures with different x values have been investigated by photoluminescence (PL), energy dispersive spectrum (EDS), and transmission electron microscopy (TEM). Experimental results suggested that the composition of epitaxial layers evidently affected the microstructure of the heterostructures. When x value was close to 0.5, the defects in the epitaxial layer decreased, and the lattice match between film and substrate approached optimum. Meanwhile, the heterostructure provided a high luminescence efficiency.

Low-temperature heteroepitaxial growth of SiGe on Si with low-pressure chemical vapor deposition

SiGe heteroepitaxial layers were grown on (001)Si substrates by low-pressure CVD using Si 2H 6 and GeH 4. The relations between the growth rates, the Ge composition of epitaxial layers, and the growth conditions such as the partial pressure of source gas and the growth temperature were studied. It was found that the Ge deposition rate is a dominant factor controlling the Ge composition and growth rate of SiGe layers. Both Si and Ge component deposition rates are enhanced by Ge deposited on the growth surface. This suggests that the surface Ge atom acts as a catalyst for the decompositions of both Si 2H 6 and GeH 4. Nonlinearity observed in the dependence of the SiGe growth rate on the GeH 4 partial pressure can be explained by taking account of this catalysis. Activation energies in Si, SiGe and Ge depositions were estimated to be 1.7, 1.5, and 0.5 eV. For growth of SiGe, the activation energy almost never depends on the Ge composition. It was found that the deposition kinetics of the Ge atom in pure Ge growth differ greatly from those in the SiGe growth.

Determination of Ga1− xAlxAs epitaxial layer composition by X-ray intensity measurements of quasi-forbidden reflections

A method of Al-content determination in Ga 1− x Al x As layers is proposed. It consists in X-ray diffraction investigation of integrated intensity of weak quasi-forbidden reflections. Their known property is utilized such that, due to the peculiarities of the structure factor, these reflections are sensitive to composition. Applicability of the method is demonstrated on results obtained for epitaxial Ga 1− x Al x As layers grown on (100) GaAs substrate by liquid phase electroepitaxy (LPEE). The choice of the most suitable reflection is discussed. It is shown that in general case the reflection 006, for which the influence of the defect structure on intensity is weak, should be applied rather than 002. The methof is most useful in the range 0< x<0.4 where the estimated error, ν x, does not exceed 0.02.

Internal strain and lattice deformation of molecular-beam-epitaxy-grown GaInAsSb on GaAs substrate

The X-ray double-crystal diffraction technique has been applied to a study of the internal strain and lattice deformation of GaInAsSb epitaxial layers grown on GaAs substrate by molecular beam epitaxy. The results reveal a more complicated unit cell geometry of the GaInAsSb film which is different from the usually assumed tetragonal deformation plus an external tilt of the epilayer unit cell. Theoretical values of lattice mismatch Δa/avs. Ga1−xInxAs1−ySby epitaxial layer composition y at various lasing wavelengths are presented and compared with the experimental results. It is found that for a given lasing wavelength, e.g. 2.6 μm, Δa/a exhibits a minimum value over the entire composition range, thus expecting GaInAsSb to have the minimum internal strain at this critical point, which may be used as a guide to achieve the best-structure device design. Misorientation between the GaInAsSb epitaxial layer and GaAs substrate was observed and has been characterized more precisely with the presented X-ray double-crystal diffraction formalism.

Gas source MBE of InP and GaxIn1−xPyAs1−y : Materials properties and heterostructure lasers

The growth of useful GaxIn1−xPyAs1−y by MBE is inhibited by the difficulty in maintaining precise control over the flux from condensed source As and P effusion ovens. The use of P2 and As2 beams generated from the cracking of PH3 and AsH3 as an alternative approach is reviewed and new data are presented. Accommodation coefficients were determined for P2 and As2 on heated InP and GaAs surfaces. The flux composition as a function of epitaxial layer composition was determined for the lattice-matching quaternary. Studies of doping were done and injection laser structures were grown. Although detailed studies of layer composition control were not done, the achievable control seems quite adequate for injection lasers. A variety of heterostructure lasers emitting at nominally 1.5 μm with broad area 300-K threshold-current densities from 1300 to 2400 A/cm2 were demonstrated. Ridge waveguide lasers fabricated from the same wafers had Ith of about 40 mA and differential efficiencies of 36%–45%. They lased cw to 50 °C.

Preparation and investigation of some properties of epitaxial layers of the solid solution system

In this paper we give the experimental results of an investigation of the growth process, morphology, structure, and composition of epitaxial layers of the solid solution system ZnGeP2-GaP. It is established that the chemical transfer mechanism for ZnGeP2 in a closed system with the transport agent ZnCl2 is analogous to the transfer mechanism of binary semiconductors and takes place with the decomposition of the compound into its elements. It is demonstrated that when ZnGeP2 is deposited on substrates of GaP monocrystalline films of the solid solution ZnGeP2-2GaP are formed, the composition of which varies along the thickness of the film from 1∶3 at the boundary with the substrate to 1∶1 in the stationary region for the boundary. The films have a zinc blende structure given by the replacement of Zn and Ge in the sites of the cation sublattice of ZnGeP2 by gallium, which enters into the gas phase from the substrate during its gas etching before the start of the growth.

High resolution transmission electron microscopy (HRTEM) of interfaces in epitaxial ZnSe yS 1 − y grown by MOCVD

The preparation of cross-sectional samples of a number of epitaxially grown, binary and ternary materials within the system ZnSe 1 − y S y (0 ⪕ y ⪕ 1) on a variety of single crystalline substrates is reported. A combination of chemical polishing and fast atom bombardment (FAB) provides samples down to ca. ⪕ 100 Å thickness and these are suitable for study by high resolution (lattice imaging) transmission electron microscopy (HRTEM). The integrity of the structure and composition of epitaxial layers appears to be maintained during thinning and our techniques allow the selection and subsequent thinning of particular regions of interfaces. The lattice images obtained at 100 and 120 keV reveal structural details of the interfaces and defects in the bulk of the epiaxial layers.

Growth and Characterization of Ga0.47In0.53As Films on InP Substrates Using Triethylgallium, Triethylindium, and Arsine

Lattice matched epitaxial layers of on substrates are of current interest in a number of device applications. In this paper, we report on the growth of such epitaxial layers using organometallic chemical vapor deposition with triethylgallium (TEG), triethylindium (TEI), and arsine for the reactant species. A conventional, atmospheric pressure reactor system was used for these experiments. The depletion reaction between TEI and arsine has been modeled and a theory predicting the epitaxial layer composition as a function of the reactant pressures at the inlet has been developed, based on this model. The inclusion of an in situ substrate etching step has been found to significantly improve the surface morphology of the grown layer and resulted in mirror‐like surfaces. The effect of lattice mismatch is shown to be much worse for layers in tension than for layers in compression.