Initial Stage Of Epitaxial Growth Research Articles

Growth of High-Quality GaAs on Ge by Controlling the Thickness and Growth Temperature of Buffer Layer

High-quality GaAs thin films grown on miscut Ge substrates are crucial for GaAs-based devices on silicon. We investigate the effect of different thicknesses and temperatures of GaAs buffer layers on the crystal quality and surface morphology of GaAs on Ge by metal-organic chemical vapor deposition. Through high resolution x-ray diffraction measurements, it is demonstrated that the full width at half maximum for the GaAs epilayer (Ge substrate) peak could achieve 19.3 (11.0) arcsec. The value of etch pit density could be 4×104 cm−2. At the same time, GaAs surfaces with no pyramid-shaped pits are obtained when the buffer layer growth temperature is lower than 360°C, due to effective inhibition of initial nucleation at terraces of the Ge surface. In addition, it is shown that large island formation at the initial stage of epitaxial growth is a significant factor for the final rough surface and that this initial stage should be carefully controlled when a device quality GaAs surface is desired.

Phase Transformation of Molecular Beam Epitaxy-Grown Nanometer-Thick Gd2O3 and Y2O3 on GaN

High quality nanometer-thick Gd₂O₃ and Y₂O₃ (rare-earth oxide, R₂O₃) films have been epitaxially grown on GaN (0001) substrate by molecular beam epitaxy (MBE). The R₂O₃ epi-layers exhibit remarkable thermal stability at 1100 °C, uniformity, and highly structural perfection. Structural investigation was carried out by in situ reflection high energy electron diffraction (RHEED) and ex-situ X-ray diffraction (XRD) with synchrotron radiation. In the initial stage of epitaxial growth, the R₂O₃ layers have a hexagonal phase with the epitaxial relationship of R₂O₃ (0001)(H)<1120>(H)//GaN(0001)(H)<1120>(H). With the increase in R₂O₃ film thickness, the structure of the R₂O₃ films changes from single domain hexagonal phase to monoclinic phase with six different rotational domains, following the R₂O₃ (201)(M)[020](M)//GaN(0001)(H)<1120>(H) orientational relationship. The structural details and fingerprints of hexagonal and monoclinic phase Gd₂O₃ films have also been examined by using electron energy loss spectroscopy (EELS). Approximate 3-4 nm is the critical thickness for the structural phase transition depending on the composing rare earth element.

Basal Plane Dislocation Mitigation in SiC Epitaxial Growth by Nondestructive Substrate Treatment

An optimized molten KOH–NaOH–MgO eutectic mixture is used to pretreat the 8° off-axis 4H-SiC substrate prior to chemical vapor deposition epitaxial growth. Superior to the conventional pure KOH etching method, by way of the eutectic method, the conversion of basal plane dislocation (BPD) to threading edge dislocation in the subsequent epitaxial growth is independent of the etch pit size pregenerated on the substrate. Even with a very mild treatment using the eutectic mixture, which does not generate discriminable etch pits on the substrate, an epilayer with low BPD density <22 cm–2 (<0.1% of BPDs on the substrate) is still achieved, and further, there is no degradation of morphology on the entire sample surface. All of the BPD conversions occur at the initial stage of epitaxial growth.

Influence of substrates on epitaxial growth of B-site-ordered perovskite La2NiMnO6 thin films

Epitaxial La2NiMnO6 films were grown on (100)-oriented SrTiO3 and (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (LSAT) substrates under various growth conditions by pulsed laser deposition. Ferromagnetism and transport properties of B-site-ordered perovskite are greatly influenced by growth conditions. Optimum growth conditions of epitaxial La2NiMnO6 films, which exhibit the ferromagnetism similar to bulk properties, are different for SrTiO3 and LSAT substrates probably due to the difference in surface migration. Since the initial stage of epitaxial growth might vary with the type of substrates, the ordering of Ni and Mn ions is different. Therefore, the ferromagnetism of La2NiMnO6 depends on the epitaxial growth conditions and type of substrates.

Superstructure phase transitions in Ge on Si (111) at the initial stage of epitaxial growth

The surface phase transitions 7 × 7 → 5 × 5 for two-dimensional and c2 × 8 →7 × 7 and 7 × 7 → c2 × 8 for three-dimensional Ge islands epitaxially grown on Si(111) were found experimentally using scan- ning tunneling microscopy. The first two transitions are associated with an increase in the level of misfit strains, while the last is related to a decrease in the stress level during plastic relaxation.

Electron-microscopic investigation of a SiC/Si(111) structure obtained by solid phase epitaxy

First results of the electron-microscopic investigation of thin silicon carbide (SiC) layers grown on silicon using a new method of solid phase epitaxy are presented. It is shown that, at the initial stage of epitaxial growth, a transition layer is formed which consists of various SiC polytypes. This layer occurs at the interface between the substrate and a single-crystalline SiC layer possessing predominantly a 3C polytype structure. It is established that pores with dimensions ranging from a fraction of micron to several dozen nanometers are formed in a near-surface layer of the silicon substrate, which favor the growth of epitaxial, weakly strained single-crystalline SiC layers.

The simulation of epitaxy, sublimation, and annealing processes in a 3D silicon surface layer

The Monte Carlo model for simulating epitaxy, sublimation, and annealing of the (111) surface of a diamond-like crystal is developed. The model accounts for the so-called overhanging structures and allows one to consider a 3D surface layer with a complex structure and volume comprising as many as 107 atom sites. The initial stage of epitaxial growth on smooth as well as on porous surfaces and the annealing of both step-containing and porous surfaces are simulated. The effect of Schwoebel barriers on the formation of compact 3D islands during epitaxy is suggested as a possible kinetic mechanism for quantum-dot formation. The sublimation behavior of monatomic steps on the (111) surfaces of a diamond-like crystal is also studied.

Structural Transformation of Screw Dislocations via Thick 4H-SiC Epitaxial Growth

In this paper, we studied the structural transformation of screw dislocations through gas-phase 4H-SiC epitaxial growth. We confirmed based on the numbers and features of etch pits on a surface after KOH treatment that some micropipes were closed in the epitaxial layer, and were divided into several elementary screw dislocations. We discuss the magnitude of Burgers vectors of micropipes in 4H-SiC substrates in relation to the number of elementary screw dislocations generated by micropipe closing. A depth analysis further revealed that most micropipe closings took place in the initial stage of epitaxial growth.

Atom diffusion during MBE growth on patterned substrate

MBE growth on patterned substrate has been studied by means of transmission electron microscopy (TEM). The surface morphology development during the initial stage of epitaxial growth and the lateral epilayer thickness variation have been studied on a nanometer scale. A diffusion model has been proposed to explain the observed phenomena. Based on this diffusion model, it is proved that the diffusion length of adatoms on (100) plane can be measured from the cross-sectional shadow image as well as the cross-sectional TEM images of the grown layers. Again, from the diffusion model, it is found that Ga adatoms diffusion length ratio on (115A) over that on (100) can be measured from the GaAs layer thickness variation on (100) and at the intersection between (100) and (115A). The ratio of Ga adatoms diffusion length on (115A) over that on (100) is reported for the first time.

Adatom migrations and nucleations on reconstructed (001) surfaces I. Si

Single Si adatom migration and the initial stage of epitaxial growth on (2 × 1) reconstructed Si(001) surfaces were investigated by an ab initio method using density functional theory. The obtained results are as follows: (a) the most stable binding site of a single Si adatom is different from the position that is required by epitaxial growth; (b) two Si adatoms interacting in order to produce a dimer take just the positions required for epitaxial growth. We conclude that the extreme stability of the Si dimer compared to other structures generated from two Si adatoms interacting on Si(001) surfaces is the origin of the formation of the perpendicular dimer rows alternately layer by layer on the reconstructed Si(001) surface in the process of epitaxial growth.

CVD Growth of SiC on Ultrathin SOi2: A Step Towards Development of a Compliant Substrate for SiC and III-V Compounds

ABSTRACTThis paper addresses the initial stage of epitaxial growth of SiC on thin (about 300A) and thick (2000Å) Si films. Our results as obtained by Rutherford backscattering spectroscopy (RBS), Auger spectroscopy, and plan-view/cross-sectional TEM, demonstrate epitaxial growth of 3C-SiC structures on ultrathin Si films (even under non-optimized growth conditions). These preliminary results indicate that the crystalline quality of SiC on thin SIMOX is better than that grown on thick SIMOX or bulk Si substrates. Growth of SiC epi on thin Si will pave the way for growth of SiC directly on SiO2 (a compliant substrate) by carbonization of the entire thin Si top layer of SIMOX.

Structural Correlation among Different Phases in the Initial Stage of Epitaxial Growth of Au on Si(111)

Structures created on the Si(111) substrate in the presence of Au atoms corresponding to coverages (θ; Au) of ∼0.7–1.4 monolayers (ML) are discussed on the basis of the observed scanning tunneling microscopy images. At small θ; Au's ( ∼0.7–1.0 ML), a √3×√3 phase and a less-ordered phase coexist, the fractional area of the latter being increased with increasing θ; Au, and at larger θ; Au's (\\stackrel>∼ 1.1 ML), a 6×6 phase appears as a single phase, in agreement with previous reports. It is shown that the less-ordered phase coexisting with the √3×√3 phase already has a close relation to the 6×6 phase in structure. The most fundamental structure of the 6×6 phase is seen at a large θ; Au of ∼1.4 ML, in which a layer of Au atoms sits on the Si(111) substrate incommensurately. As θ; Au decreases, some Au atoms appears to be removed with a periodicity of 6×6. The Au coverage of the √3×√3 phase seems to be ∼2/3 ML.

In-Situ Observation of Chemical Vapor Deposition of Thin Sige Films by Optical Reflection Interferometry

AbstractChemical Vapor Deposition of Si1-x Gex – films on Si (100) and of polycrystalline Si1-x Gex, layers on SiO2 – coated substrates have been performed at a pressure of 200 Pa in the temperature range of 500°C – 800°C, correspondingly. To observe the growth process and to characterize the growing thin films at deposition conditions an optical reflection interferometer (PYRITIERS) has been used. Comparing the data obtained at growth temperature with ex- situ measurements by spectroscopic ellipsometry the temperature dependence of optical constants of SiGe films have been evaluated. The reflectivity measurements during the deposition process allow to study the quality of the heteroepitaxial film, even in the initial stage of epitaxial growth.

The effects of the growth parameters on the initial stage of epitaxial growth of GaP on Si by metalorganic chemical vapor deposition

The effects of growth parameters (V/III ratio, growth pressure and substrate orientation) on the initial stage of the epitaxial growth of GaP on Si are described. It was found that a high V/III ratio is necessary to grow a smooth GaP layer on Si and that the V/III ratio where the growth mode changes from island-type to two-dimensional layer-type decreases with increasing growth pressure. A growth technique for obtaining a smooth GaP layer on Si and the nucleation mechanisms are made clear using these results.

Real time measurement of crystal growth by glancing angle scattering of fast ions

We have constructed a new system for real time measurements of crystal growth by glancing angle scattering of fast ions. The system is composed of a microchannel plate, a fluorescence screen and a CCD video camera in order to measure the dynamical change in the angular distribution of the scattered ions during crystal growth. Initial stage of epitaxial growth of lead chalcogenides on SnTe (100) under UHV conditions is studied with the system. Anomalous broadening of the angular distribution of scattered 0.7-MeV He ions is observed when the thickness of the growing layer is between 1 and about 10 nm. From the Monte Carlo simulation of ion trajectories at glancing angle scattering from several model surfaces, this anomaly is attributed to the surface wrinkles caused by a square network of misfit edge dislocations.

Cleaning during Initial Stages of Epitaxial Growth in an Ultrahigh Vacuum Rapid Thermal Chemical Vapor Deposition Reactor

AbstractIn this paper, we report our results on surface preparation for the growth of epitaxial Si films. Hydrogen passivated surfaces are currently being investigated for application in Si epitaxy to eliminate the high temperature in-situ bake necessary to remove the native oxide. Hydrogen passivation is obtained by a dilute HF dip before the substrate is loaded in the process chamber. However the passivation is partially lost when the HF dip is followed by a water rinse which results in oxygen absorption on the substrate. It was found that the peak oxygen concentration at the epitaxy substrate interface increase by an order of magnitude due to a five minute water rinse. We report here that oxygen and carbon at the epitaxy substrate interface can be desorbed during initial stage of epitaxial growth by reducing epitaxial growth rate. In this work, epitaxial Si films were deposited over a wide range of growth rates obtained by varying Si2H6 flow rates. The peak oxygen concentration decreases by an order of magnitude by changing the growth rate from 3000 to 700Å/kminute for a deposition temperature of 800°C. We believe that at higher growth rates Si overgrows on absorbed oxygen maintaining epitaxial alignment reflected in the good electrical quality of the epitaxial films. However, at low growth rates oxygen has sufficient time to desorb before overgrowth can take place, improving the epitaxy substrate interface quality.

Initial stage of epitaxial growth at low temperature of GaAs and AlAs on Si by atomic layer molecular beam epitaxy (ALMBE) and MBE

First stages of GaAs, AlAs and GaAs-on-AlAs growth on Si by atomic layer molecular beam epitaxy (ALMBE) and conventional MBE has been studied by in situ RHEED and Auger electron spectroscopy (AES) techniques and by high resolution electron microscopy (HREM) after growth. Our results allow us to assess the growth conditions necessary to achieve monolayer by monolayer growth of GaAs on Si.

STM study of SiC crystallite growth on vicinal Si(111) surfaces

The initial stage of epitaxial growth of cubic β-SiC on vicinal Si(111) misoriented towards the [112̄] direction is studied by scanning tunneling microscopy in ultra-high vacuum. The clean Si(111) surface contains terraces separated by groups of atomic steps. The separation between the atomic steps within a group is observed to be approximately equal to the length of the long axis of the Si(111)7 × 7 unit cell. We postulate that the SiC forms three-sided pyramids with surfaces of (110) orientation. The pyramids are located mostly at the step edges and are sharper than the end of the tip. This results in a series of identically shaped tip images located at the step edges, which display the structure of the tip.

STM study of initial stage of Ge epitaxy on Si(001)

A scanning tunneling microscope (STM) was employed to study the superstructures and the formation process of islands at the initial stage of epitaxial growth of Ge layers on the Si(001) surface. Amount of Ge deposition was varied from one half of a monolayer (ML) to 4 ML. At a low Ge coverage the Ge layers were developed at step edges and on terraces forming two-dimensional (2D) islands and exhibited c(4 × 2) and p(2 × 2) structures on the Si substrate at 300°C. At a higher coverage of about 2 ML, a new superstructure with a periodicity of about 7 times of the unit cell was observed and the new cells were found to be the cores of the 3D islands. The number of islands increased and the islands grew with Ge coverage. Most Ge islands disappeared by annealing at 500°C and the 2D superstructure appeared again. Formation and growth mechanisms of the 3D Ge islands and the relaxation of the stress due to Si-Ge lattice mismatch will be discussed in analyzing the observed STM images.

The initial stage of epitaxial growth of Ge on Ge(111) as studied by X-ray diffraction

We present an in situ X-ray scattering study of the evolution of surface structure and morphology during deposition of Ge on Ge(111). The substrate temperature (300 K) was such that the growth proceeds through two-dimensional nucleation. We determined the sites on the c(2 × 8) reconstructed Ge(111) surface to which the first deposited Ge atoms bond. The arrangement of the deposited atoms was inferred from an analysis of the diffracted intensities along the integer-order rods of Bragg scattering perpendicular to the surface plane. We find the first deposited Ge atoms to occupy adsorption sites above the “rest atoms” in the reconstructed unit cell. For higher coverages islands of bilayer height are formed.