Synthesis of epitaxial silicon carbide films through the substitution of atoms in the silicon crystal lattice: A review

A review of recent advances in the field of epitaxial growth of SiC films on Si by means of a new method of epitaxial substitution of film atoms for substrate atoms has been presented. The basic statements of the theory of the new method used for synthesizing SiC on Si have been considered and extensive experimental data have been reported. The elastic energy relaxation mechanism implemented during the growth of epitaxial SiC films on Si by means of the new method of substitution of atoms has been described. This method consists in substituting a part of carbon atoms for silicon matrix atoms with the formation of silicon carbide molecules. It has been found experimentally that the substitution for matrix atoms occurs gradually without destroying the crystalline structure of the matrix. The orientation of the film is determined by the “old” crystalline structure of the initial silicon matrix rather than by the silicon substrate surface only, as is the case where conventional methods are used for growing the films. The new growth method has been compared with the classical mechanisms of thin film growth. The structure and composition of the grown SiC layers have been described in detail. A new mechanism of first-order phase transformations in solids with a chemical reaction through an intermediate state promoting the formation of a new-phase nuclei has been discussed. The mechanism providing the occurrence of a wide class of heterogeneous chemical reactions between the gas phase and a solid has been elucidated using the example of the chemical interaction of the CO gas with the single-crystal Si matrix. It has been shown that this mechanism makes it possible to grow a new type of templates, i.e., substrates with buffer transition layers for growing wide-band-gap semiconductor films on silicon. A number of heteroepitaxial films of wide-band-gap semiconductors, such as SiC, AlN, GaN, and AlGaN on silicon, whose quality is sufficient for the fabrication of a wide class of micro- and optoelectronic devices, have been grown on the SiC/Si substrate grown by solid-phase epitaxy.     

缓冲层对InSb/GaAs薄膜质量的影响

InSb是制作3~5μm红外探测器的重要材料。在GaAs衬底上外延生长InSb,存在的主要问题在于两种材料间14.6%的晶格失配度,会引入较大的表面粗糙度以及位错密度,使外延材料的结构和电学性能均会受到不同程度的影响。通过系列实验,研究了在生长过程中缓冲层对薄膜质量的影响。利用高能电子衍射仪(RHHEED)得到了合适的生长速率和Ⅴ/Ⅲ比,研究了异质外延InSb薄膜生长中低温InSb缓冲层对材料生长质量以及不同外延厚度对材料电学性质的影响。采用原子力显微镜(AFM)、透射电子显微镜(TEM)、X射线双晶衍射(DCXRD)等方法研究了InSb/GaAs薄膜的表面形貌、界面特性以及结晶质量。通过生长合适厚度的缓冲层,获得了室温下DCXRD半高峰宽为172″,77 K下迁移率为64300 cm²·V^-1·s^-1的InSb外延层。     

Formation of CrSi2 nanoislands on Si(111)7 × 7 and epitaxial growth of silicon overlayers in Si(111)/CrSi2 nanocrystallites/Si heterostructures

Low-energy electron diffraction and differential reflectance spectroscopy are used to study the self-formation of chromium disilicide (CrSi₂) nanoislands on a Si(111) surface. The semiconductor properties of the islands show up even early in chromium deposition at a substrate temperature of 500°C, and the two-dimensional growth changes to the three-dimensional one when the thickness of the chromium layer exceeds 0.06 nm. The maximal density of the islands and their sizes are determined. The MBE growth of silicon over the CrSi₂ nanoislands is investigated, an optimal growth temperature is determined, and 50-nm-thick atomically smooth silicon films are obtained. Ultraviolet photoelectron spectroscopy combined with the ion etching of the specimens with embedded nanocrystallites demonstrates the formation of the valence band, indicating the crystalline structure of the CrSi₂. Multilayer epitaxial structures with embedded CrSi₂ nanocrystallites are grown.     

Grazing‐incidence X‐ray diffraction study of rubrene epitaxial thin films

The growth of organic semiconductors as thin films with good and controlled electrical performances is nowadays one of the main tasks in the field of organic semiconductor‐based electronic devices. In particular it is often required to grow highly crystalline and precisely oriented thin films. Here, thanks to grazing‐incidence X‐ray diffraction measurements carried out at the ELETTRA synchrotron facility, it is shown that rubrene thin films deposited by organic molecular beam epitaxy on the surface of tetracene single crystals have the structure of the known orthorhombic polymorph, with the (2 0 0) plane parallel to the substrate surface. Moreover, the exact epitaxial relationship between the film and the substrate crystalline structures is determined, demonstrating the presence of a unique in‐plane orientation of the overlayer.     

Influence of the surface morphology of single-crystal Si(111) substrates on the magnetic properties of epitaxial cobalt films

The epitaxial films Co(111)/Cu(111)-R30°/Si(111) have been grown on the atomically smooth and vicinal Si(111) surfaces. The roughnesses of the substrate and the cobalt film have been determined using scanning tunneling microscopy. The dependence of the coercive force has been investigated as a function of the azimuthal angle. The dependence of the magnetic anisotropy and the coercive force on the surface roughness has been determined. It has been shown that, in the epitaxial cobalt films deposited on the atomically smooth silicon surfaces, crystalline anisotropy of the 〈110〉 type leads to the isotropy of the magnetization reversal processes. The step-induced uniaxial anisotropy has been observed upon deposition on the vicinal surfaces. The films deposited on the atomically smooth surfaces have a complex domain structure.     

X-ray diffraction characterization of MBE grown Pr1−xSrxMnO3 thin films on NGO(1 1 0)

Oxygen plasma-assisted molecular beam epitaxial (MBE) growth of Pr_1−xSr_xMnO₃ (PSMO) thin films has been carried out on NdGaO₃(1 1 0) (NGO) substrates. The growth parameters have been optimized to realize 2D layer-by-layer growth. XRD results of the epilayers show that the PSMO/NGO(1 1 0) thin films are of high crystal quality, as clear diffraction peaks can be observed belonging to the film and the substrate, respectively. Based on analysis of the peaks, it was concluded that epitaxial relation is PSMO(1 1 0)//NGO(1 1 0), i.e., the c-axis being parallel to the surface. Both single scans (ω scan, 2θ/ω scan) and 2-axis reciprocal space mapping (RSM) were performed in an effort to assess the crystal structure, crystalline quality, surface and interface properties of the epitaxial layers. High temperature annealing effects on lattice structure and crystal quality have been studied and discussed. Transport property measurement of the PSMO thin film samples has been carried out and main features discussed.     

An atomically controlled Si film formation process at low temperatures using atmospheric-pressure VHF plasma

To grow epitaxial Si films with atomic- and electronic-level perfection, a high-temperature chemical vapor deposition (CVD) process (>1000 °C) has been generally employed. To reduce the growth temperature below 600?°C but keeping a high deposition rate, other energy sources than thermal heating are required. Atmospheric pressure plasma CVD (AP-PCVD) is considered to be suitable for fabricating high-quality films at high deposition rates due both to the high radical density and to the low ion bombardment against the film surface, because the collision frequency among ions and neutral atoms is high. The present study focuses on the low-temperature growth of epitaxial Si, and experimentally demonstrates that AP-PCVD is capable of growing epitaxial Si films with high perfection applicable for semiconductor devices. It is found that the pre-growth cleaning of the Si surface by H(2) AP plasma is effective to grow high-purity Si films, and that the exposure of a film-growing surface to AP plasma during growth is important to form particle-free and defect-free Si films. From the experimental results and the first-principles molecular dynamics simulations of surface atomic reactions, it can be mentioned that both H atoms in the AP plasma and high-density He atoms having thermal kinetic energy contribute to the reduction of growth temperature by supplying considerable energy to the surface.     

Controlled growth of complex polar oxide films with atomically precise molecular beam epitaxy

At heterointerfaces between complex oxides with polar discontinuity, the instability-induced electric field may drive electron redistribution, causing a dramatic change in the interfacial charge density. This results in the emergence of a rich diversity of exotic physical phenomena in these quasi-two-dimensional systems, which can be further tuned by an external field. To develop novel multifunctional electronic devices, it is essential to control the growth of polar oxide films and heterointerfaces with atomic precision. In this article, we review recent progress in control techniques for oxide film growth by molecular beam epitaxy (MBE). We emphasize the importance of tuning the microscopic surface structures of polar films for developing precise growth control techniques. Taking the polar SrTiO₃ (110) and (111) surfaces as examples, we show that, by keeping the surface reconstructed throughout MBE growth, high-quality layer-by-layer homoepitaxy can be realized. Because the stability of different reconstructions is determined by the surface cation concentration, the growth rate from the Sr/Ti evaporation source can be monitored in real time. A precise, automated control method is established by which insulating homoepitaxial SrTiO₃ (110) and (111) films can be obtained on doped metallic substrates. The films show atomically well-defined surfaces and high dielectric performance, which allows the surface carrier concentration to be tuned in the range of ~10¹³/cm². By applying the knowledge of microstructures from fundamental surface physics to film growth techniques, new opportunities are provided for material science and related research.     

The nature of molecular beam epitaxial growth examined via computer simulations

Man-made synthetic structures involving epitaxially grown thin films of one or more compound semiconductors have been finding an increasingly important role in semiconductor device technology.¹ Remarkable advances have been made over the past decade in the realization of a variety of such structures involving III-V, II-VI. and IV-VI compound semiconductors, as well as combinations of semiconductors with dielectrics and metals.' The major part of this progress has come about primarily due to the advent of, and refinements in, two vapor phase growth techniques — molecular beam epitaxy (MBE)' and metal-organic chemical vapor deposition (MO-CVD).³ The underlying motivation has been the remarkably altered and potentially useful electronic and optical properties of electrons, holes, and light arising from their confinement in a quasi-two-dimensional environment in the ultrathin films (thickness less than the particle deBroglie wavelength).⁴ However, confinement of the par- ticles in such ultrathin layers (typically 10 to 200 Å) places stringent requirements on the atomic level structural and chemical perfection of the films and their interfaces involved. At the same time, spatial control of the abruptness (in the growth direction) and uniformity (in the planes normal to the growth direction) of dopant distribution becomes equally sig- nificant in realizing the potential electrical and optical properties of camers and light in such structures. Both MBE and MO-CVD have been shown to meet these stringent requirements for the growth of III-V compound semiconductors, although differences between materials and structures produced by these techniques also remain. The purpose of this article is to review the progress made in understanding the process of MBE growth with particular focus on computer simulations of the growth proess.^1–15 These simulations have provided con- siderable insight into the role played by the atomistic surface kinetic processes in controlling the morphology of the growing surfaces and consequently the resulting nature of the interfaces formed upon deposition of another material on such surfaces.     

Control of MBE, MOMBE and CBE growth using RHEED

This article discusses the application of reflection high energy electron diffraction (RHEED) to the control of growth by molecular beam epitaxy (MBE), metal-organic MBE (MOMBE) and chemical beam epitaxy (CBE). RHEED can be used to control the growth rate and composition for all three techniques. In addition, it has been used to control substrate temperature using changes in surface structure. It has also been used to obtain important information on the dynamics of the growth process. From this sort of data, a rather complete picture of the epitaxial process has been obtained. This has led to these UHV deposition techniques becoming the most important methods of growth for III-V compound semiconductor thin films.     

Dopant patterning in three dimensions during molecular beam epitaxial growth using anin-situfocused ion gun

Conventional molecular beam epitaxial (MBE) growth of III-V semiconductor material systems use a thermal silicon effusion cell as the n-type dopant source. In the technique described here, the thermal source is replaced with a scanning Si focused ion gun. It is therefore possible to directly write dopant patterns into the semiconductor waferit as it is being grown. The precise control over the elemental composition in the growth (z) direction permitted by MBE, combined with high spatial resolution of the focused dopant ion beam in the lateral (xy) plane, allows direct registration of fully integrated, three-dimensional semiconductor structures and devices otherwise unobtainable via conventional lithographic techniques. In this paper, we present electrical measurements of high mobility GaAs/AlGaAs modulation doped heterostructures fabricated using this technique.Fabrication of novel undoped channel FET structures is also discussed, where the dopant beam is used to form extended contacts to the induced electron gas. FET action is demonstrated for the first time using this technique, eliminating the constraint for self-alignment in undoped structures.     

Domain epitaxial growth of ferroelectric films of barium strontium titanate on sapphire

A model of the epitaxial growth of crystalline multicomponent films on single-crystal substrates with a domain correspondence is presented using a solid solution of barium strontium titanate on sapphire substrates (r cut). The domain epitaxial growth suggests the matching of the lattice planes of the film and the substrate having similar structures by comparison of domain multiple of an integral number of the interplanar spacings. Variation of the component composition of the solid solution enables changes in the domain size in the range sufficient for epitaxial growth. This method can be used to project the epitaxial growth of films of various solid solutions on single-crystal substrates.     

Epitaxial growth of a low-density framework form of crystalline silicon: a molecular-dynamics study

Crystal growth processes of low-density framework forms of crystalline silicon, named Si clathrates ( Si34 and Si46), during solid phase epitaxy (SPE) have been successfully observed in molecular-dynamics simulations using the Tersoff potential. The activation energy of SPE for Si34 has been found to correspond with the experimental value ( approximately 2.7 eV) for the cubic diamond phase, while the SPE rates of Si46 are much lower than that of Si34. The structural transition from Si46 to Si34 can be also observed during the Si46-[001] SPE. The present results suggest that new wide-gap Si semiconductors with clathrate structures can be prepared using epitaxial growth techniques.     

Epitaxial ferromagnetic thin films and heterostructures of Mn-based metallic and semiconducting compounds on GaAs

We present two approaches to integrate magnetic materials with III–V semiconductors. One is epitaxial ferromagnetic metallic films and heterostructures on GaAs (0 0 1) substrates. Although crystal structure, lattice constant, chemical bonding and other properties are dissimilar, ferromagnetic hexagonal MnAs thin films and MnAs/NiAs ferromagnet/nonmagnet heterostructures (HSs) are grown on GaAs by molecular beam epitaxy (MBE). Multi-stepped magnetic hysteresis are controllably realized in MnAs/NiAs HSs, making this material promising for the application to multi-level nonvolatile recording on semiconductors. The other approach is to prepare a new class of GaAs based magnetic semiconductor, GaMnAs, by low-temperature molecular beam epitaxy (LT-MBE) on GaAs (0 0 1). New III–V based superlattices consisting of ferromagnetic semiconductor GaMnAs and nonmagnetic semiconductor AlAs are also successfully grown. Structural and magnetic properties of these new heterostructures are presented.     

Magnetic properties of epitaxial Co nanodisk arrays packed on atomically smooth and vicinal Si substrates

Arrays of circular nanodisks have been formed from epitaxial Co films deposited on atomically smooth and vicinal Si(111) single crystals by using a focused Ga⁺ ion beam. The surface roughness has been determined by scanning tunneling microscopy. The coercive force and the processes of magnetization reversal in films and arrays of epitaxial Co nanodisks have been studied. It has been shown that the coercive force of the Co nanodisk arrays on the atomically smooth Si(111) surface is larger and that on the vicinal Si(111) surface is smaller than that in the epitaxial films. The studies of the magnetic structure of the nanodisks by magnetic-force microscopy in combination with the micromagnetic simulation have shown that the processes of magnetization reversal in the nanodisks on the atomically smooth substrates occur through the vortex-like states and, on the vicinal substrates, through the C-type state.     

Recent progress in perpendicularly magnetized Mn-based binary alloy films

In this article, we review the recent progress in growth, structural characterizations, magnetic properties, and related spintronic devices of tetragonal MnxGa and MnxA1 thin films with perpendicular magnetic anisotropy. First, we present a brief introduction to the demands for perpendicularly magnetized materials in spintronics, magnetic recording, and perma- nent magnets applications, and the most promising candidates of tetragonal MnxGa and MnxA1 with strong perpendicular magnetic anisotropy. Then, we focus on the recent progress of perpendicularly magnetized MnxGa and MnxA1 respec- tively, including their lattice structures, bulk synthesis, epitaxial growth, structural characterizations, magnetic and other spin-dependent properties, and spintronic devices like magnetic tunneling junctions, spin valves, and spin injectors into semiconductors. Finally, we give a summary and a perspective of these perpendicularly magnetized Mn-based binary alloy films for future applications.     

Pulsed laser deposition of lead-zirconate-titanate thin films and multilayered heterostructures

There is an increasing interest in lead-zirconate-titanate (PZT) based ferroelectric thin film and devices in recent years. Pulsed laser deposition (PLD) technique has been demonstrated to be a versatile and successful tool for the deposition of epitaxial multi-component metal oxide films and heterostructures. This review presents a reasonable understanding of the relationship between PLD processing and composition, crystal structure and orientation of PZT ferroelectric thin films, and heterostructures. Processing-related issues from PLD of PZT thin films and material-integration strategies developed to fabrication of highly oriented or epitaxial PZT thin film based capacitors with excellent ferroelectric properties are discussed in detail. PACS 81.15.Fg; 68.55.Jk; 77.22.Ej     

Study of MOCVD growth of InGaAsSb/AlGaAsSb/GaSb heterostructures using two different aluminium precursors TMAl and DMEAAl

The antimonide laser heterostructures growth technology using MBE epitaxy is currently well-developed, while MOVPE method is still being improved. It is known that the principal problem for MOVPE is the oxygen and carbon contamination of aluminium containing waveguides and claddings. The solution would be to apply a proper aluminium precursor. In this study we present the results of metal-organic epitaxy of In- and Al-containing layers and quantum well structures composing antimonide lasers devices. Special emphasis was put on the aluminium precursor and its relation to AlGaSb and AlGaAsSb materials properties. The crystalline quality of the layers grown with two different Al precursors was compared, very good structural quality films were obtained. The results suggested a substantial influence of precursors pre-reactions on the epitaxial process. The oxygen contamination was measured by SIMS, which confirmed its dependence on the precursor choice. We also optimised the GaSb substrate thermal treatment to deposit high quality GaSb homoepitaxial layers. Quaternary InGaAsSb layers were obtained even within the predicted miscibility gap, when arsenic content reached high above 10% values. InGa(As)Sb/AlGa(As)Sb quantum wells were grown and their optical properties were characterised by photoluminescence and photoreflectance spectroscopy. Type-I quantum wells showed a fundamental optical transition in the 1.9–2.1 μm range at room temperature. The epitaxial technology of the structures was subjected to an optimisation procedure. The investigated layers and heterostructures can be considered for application in laser devices.     

Influence of Silver and Gold Nanoparticles and Thin Layers on Charge Carrier Generation in InGaN/GaN Multiple Quantum Well Structures and Crystalline Zinc Oxide Films

It has been shown that Ag and Au nanoparticles and thin layers influence charge carrier generation in InGaN/GaN multiple quantum well structures and crystalline ZnO films owing to the surface morphology heterogeneity of the semiconductors. When nanoparticles 10 < d < 20 nm in size are applied on InGaN/GaN multiple quantum well structures with surface morphology less nonuniform than that of ZnO films, the radiation intensity has turned out to grow considerably because of a plasmon resonance with the participation of localized plasmons. The application of Ag or Au layers on the surface of the structures strongly attenuates the radiation. When Ag and Au nanoparticles are applied on crystalline ZnO films obtained by rf magnetron sputtering, the radiation intensity in the short-wavelength part of the spectrum increases insignificantly because of their highly heterogeneous surface morphology.     

Heteroepitaxial film growth of layered compounds with the ZrCuSiAs-type and ThCr2Si2-type structures: From Cu-based semiconductors to Fe-based superconductors

FeAs-based layered superconductors such as F-doped LaFeAsO have recently been investigated intensively because of their high superconducting transition temperatures. Epitaxial films of these compounds are important to examine their intrinsic materials properties as well as to transfer them to device applications. In this review, we first present our research route from transparent p-type oxides semiconductors to the Fe-based superconductors. Then we review growth of epitaxial thin films for the layered oxychalcogenides and oxypnictides. Reactive solid-phase epitaxy technique was inevitable to prepare epitaxial thin films of the oxychalcogenides and Zn-based oxypnictides. On the other hand, epitaxial thin films of Mn-based oxypnictides were grown by standard pulsed laser deposition. These techniques, however, did not grow epitaxial thin films for LaFeAsO. Thus, we developed a modified pulsed laser deposition process and succeeded in obtaining epitaxial thin films of FeAs-based superconductors, LaFeAsO and cobalt-doped SrFe₂As₂.