Single-crystal Epitaxial Films Research Articles

Structure determination of metastable cobalt films.

The bulk atomic structure of cobalt films deposited on GaAs has been unequivocally determined to be the body-centered-cubic metastable phase. A comparison of the conversion-electron x-ray-absorption fine structure of Co films deposited on GaAs(110) with similar measurements for the stable phases of hcp Co, fcc Cu, and bcc Fe establishes the Co bcc phase with a lattice constant of 2.82\ifmmode\pm\else\textpm\fi{}0.01 A\r{}. Furthermore, this first application of the technique to single-crystal epitaxial films shows it to be a most powerful procedure for establishing their crystal structure.

Thin Epitaxial Silicon Regrowth Using Ion Implantation Amorphization Techniques

An ion implantation amorphization technique for the preparation of thin epitaxially regrown silicon layers has been studied. 28Si+ ions are implanted into low pressure chemical vapor deposition (LPCVD) silicon films which have been deposited on silicon wafers. This causes amorphization of the films and dispersal of the buried native oxide layer on the wafers. Subsequent thermal annealing results in epitaxial regrowth of the amorphized films. The resultant crystal quality of the regrown films and substrates was studied by x‐ray, Raman, Rutherford backscattering, wet chemical etching, and electrical measurements. The influence of the different process variables was investigated. Although single crystal regrown epitaxial films are obtained, the substrates are damaged. This is probably a combined result of the implant damage, ion mixing, and precipitation of the driven in oxygen. Improvements to the process are discussed.

Ionized Cluster Beam Epitaxy of Single Crystal Metal Films on Semiconductors and Insulators

ABSTRACTOur experiments show that ionized cluster beams (ICB) can form epitaxial Al films on Si(111) and Si(100) substrates. This is unique because the lattice misfit of this material combination is more than 25%. Al can also be epitaxially grown on CaF2 films deposited on Si substrates. The initial stage of the film formation is measured by in-situ electron diffraction. In the case of Al(111) growth on Si(111) and CaF2, growth of mixed layers of different epitaxial islands of approximately 20–50 Angstrom thickness on the substrate surface is observed. With increase of thickness, the film shows the single crystal state with a flat surface, which indicates the epitaxial single crystal film formation on CaF2 or on Si substrates. It should be noted that in the Al/CaF2/Si (MIS) structure, the epitaxial CaF2 is a good insulating layer, which can be used to prepare three dimensional devices. These results show that the kinetic energy and the ionic charge of cluster ions have much influence on surface and interface modification, and that ICB is capable of producing films of good quality at low substrate temperatures.

Optical, Vibrational and Surface Properties of SiC

ABSTRACTA short historical introduction concentrates on key experimental and theoretical developments prior to the mid-seventies which form the basis of our present understanding of the semiconducting and optical properties of the polytypes of SiC. Selected research of the last decade is reviewed. Finally, we discuss our on-going surface and defect studies in both epitaxial single crystal films of 3C SiC and other hexagonal SiC polytypes.

Properties and ion implantation of AlxGa1−xN epitaxial single crystal films prepared by low pressure metalorganic chemical vapor deposition

High quality single crystal films of AlxGa1−xN have been grown on sapphire substrates using low pressure metalorganic chemical vapor deposition at 915 °C over the entire range of x. Electrical and optical properties of the layers were measured. Electrical compensation by Be+ and N+ implants in the layers was studied. Schottky barriers were fabricated and their current voltage characteristics were studied. We also report some initial results of a study of GaN growth kinetics.

Optical and thermal properties of BeO thin films prepared by reactive ionized-cluster beam technique

Preparation of BeO thin films is successfully achieved by the reactive ionized-cluster beam technique developed by the authors. Transparent BeO films with the c-axis preferential orientation which is peculiar to a hexagonal structure are obtained on glass substrates, and single-crystal epitaxial films are formed on sapphire substrates at low substrate temperatures up to 400 °C. Optical and thermal transport properties of films are investigated in detail. A strong reststrahlen reflection peak is observed in the vicinity of wavelength 13.5 μm, from which the frequencies of the transverse and longitudinal vibration modes are determined. Anisotropic lattice thermal conductivities parallel and perpendicular to the c axis of the films are measured, and the values of κ∥ph ?2.6 W/cm deg and κ⊥ph ?0.6 W/cm deg at 300 K are obtained. It is also shown that the thermal conductivities of BeO films are proportional to T−2 below Debye temperature ϑD?1053 K of this material.

Low temperature preparation of polycrystalline lead-tin tellurides in a lead iodide flux

Lead-tin telluride was prepared as a polycrystalline powder by heating a mixture of the component elements in a lead iodide flux at about 650°C. The powder, as prepared, can be used as raw material for single crystal growth or epitaxial film preparation.

Planar waveguides based on epitaxial films of GaAsP and GaN for integrated optics applications

An investigation was made of the main parameters of thin-film optical waveguides based on epitaxial singlecrystal films of GaAs1–xPx and GaN. The waveguide losses were determined for different wavelengths and the feasibility of using these waveguides in integrated optics was analyzed.

Thermoreflectance spectra of rf-sputtered epitaxial single-crystal films ofPbxSn1−xTe

Thermoreflectance spectra of radio-frequency sputtered epitaxial single-crystal films of ${\mathrm{Pb}}_{0.83}$${\mathrm{Sn}}_{0.17}$Te from 1.5 to 6.0 eV, at room temperature and 100 K, have been measured and studied. $\ensuremath{\Delta}{\ensuremath{\epsilon}}_{1}$ and $\ensuremath{\Delta}{\ensuremath{\epsilon}}_{2}$ have been obtained through a Kramers-Kronig analysis of the experimental room-temperature $\frac{\ensuremath{\Delta}R}{R}$ spectra. A line-shape analysis of the ${E}_{2}$ structure has been performed in conjunction with an exact derivative procedure of the interband dielectric function at Van Hove singularities. Temperature coefficients have been measured and reported.

Hot electron transport effects in lead telluride

Velocity-electric field characteristics and evidence for travelling high field domains are reported for hot-electron conduction in single crystal epitaxial films of n-PbTe. Measurements were performed at 77 K, using nanosecond pulse techniques. Contact effects cause differences in the shape of the velocity-field curve and also possibly in the nature of high-field current instabilities. Pulsed Hall measurements reveal substantial time-dependent carrier generation and may indicate the presence of high-field domains.

On the dislocation structure of low angle (110) twist boundaries and its relationship to the O-lattice

Several (110) twist boundaries in gold were examined by transmission electron microscopy. Thin film bicrystal specimens were used which were prepared by welding together single crystal epitaxial (110) gold films. Twist angles, theta, of 1/sup 0/ to 5/sup 0/ were used. The dislocation arrays were examined at 125 kV and imaged using (anti 1 11), (1 anti 1 1), (002) and (2 anti 2 0) reflections. The results emphasize the fact that the O-Lattice approach to the structure of grain boundaries may not be straightforward. In general, both simple homogeneous transformations and inhomogeneous transformations must be considered and there is no simple way to predict which may actually apply. Such procedures are equivalent, of course, to searching for the dislocation network of minimum energy.

Far-infrared reflectivity of PbTe films on NaCl substrates

In the wavenumber region 3–400 cm −1 reflectivity measurements of high quality single crystal n-PbTe epitaxial films on NaCl substrates at T = 5, 77 and 300 K have been performed. From the analysis of the data a detailed information on the variation of the optical constants and particularly of TO phonon softening with decreasing lattice temperature is obtained for samples with n ≈ 0.3−3.0 × 10 17 cm −3. In addition the frequencydependence of the carrier collision time was investigated.

Ion Implantation of Pb0.8Sn0.2Te

The ion implantations of many ions into single crystal epitaxial films of Pb0.8Sn0.2Te have been evaluated. Because of the wide spectrum of results, only those of the two most promising ions, S+ and In+, are presented. The S+ ions produced a p-type layer in Pb0.8Sn0.2Te. After a suitable post implant anneal In+ ions produced an n-type layer in p-type Pb0.8 Sn0.2Te. The In+ implants were used to produce detector arrays, while the S+ implants produced complete conversion of 4500 A films.

ChemInform Abstract: CHEMICAL VAPOR DEPOSITION OF EPITAXIAL FILMS OF YTTRIUM IRON GARNET AND GALLIUM‐SUBSTITUTED YTTRIUM IRON GARNET AND A THERMODYNAMIC ANALYSIS

AbstractDie chemische Abscheidung aus der Dampfphase von epitaktischen Einkristall?lmen der im Titel genannten Granate erfolgt durch Reaktion der gasförmigen Metallchloride mit O, bei l150°C und 5 Torr.

Epitaxial growth of garnets for thin film lasers

Liquid phase epitaxial techniques have been developed for the preparation of thin films of optical materials. Heteroepitaxy of magnetic garnets on nonmagnetic garnet substrates by the dipping technique employs the phenomenon of stable supersaturation in the iron garnet-PbO:B2O3 system. Rare earth aluminum garnets in the same flux supersaturate to a lesser extent and precipitate readily upon substrate insertion. High quality films of YAG:Nd and YAG:Yb,Er,Tm,Ho on pure YAG as well as pure YAG on YAG:Nd have been prepared from a saturated PbO:B2O3+ flux using a transfer technique. Laser oscillation of Ho3+ at 2.1μm and Nd3+ at 1.06μm in single crystal epitaxial films prepared by the transfer technique have been reported by van der Ziel et al. Solute transfer has the advantage in optic garnet systems of uniform film growth at constant temperature without spontaneous nucleation. In addition, continuous solution of uniform composition nutrient maintains the rare earth dopant concentration in the melt. Pb incorporation results in a brown discoloration but can be eliminated by the proper choice of growth temperature. Deposition rates between 2 μm and 6 μm/hr. at ∼1O00°C have been found satisfactory. In this paper melt preparation, furnace design, the effect of impurities on threshold, and the effects of lattice mismatch and substrate orientation will be discussed.

Chemical Vapor Deposition of Epitaxial Films of Yttrium Iron Garnet and Gallium‐Substituted Yttrium Iron Garnet and a Thermodynamic Analysis

Epitaxial single‐crystal films of yttrium iron garnet (YIG) and Ga: YIG (Y3Fe5‐xGaxO12) were grown by chemical vapor deposition. The garnet is deposited by the reaction of gaseous metal chlorides with O2 at 1150°C and 5 torr. The chlorides are generated in‐line by reacting Cl2 gas with a Y‐Fe(‐Ga) alloy. A computer‐aided thermodynamic calculation was developed to determine which of several possible solids in a multicomponent CVD system will be deposited for a given set of growth conditions. The calculation determines an intermediate equilibrium among all gaseous species and then identifies the solid phase most favored to be deposited from the supersaturated gas phase. The results of the calculations agreed well with experiment and have been useful in finding the conditions for optimum growth of garnet. This type of calculation can be applied to other multicomponent CVD systems.

Magnetic Bubble Devices

The properties of cylindrical magnetic “bubble” domains have been extensively described in the literature. Our understanding of bubble technology has now progressed to the point where it is possible to undertake the design and evaluation of specific bubble systems. Bubble domains, cylindrical islands of reverse magnetization, exist in specially prepared single crystal uniaxial magnetic platelets and epitaxial films. These domains are manipulated by localized magnetic fields generated by currents applied to conductors (conductor access) or inplane fields applied to structured permalloy patterns (field access). An important application of bubbles will be in bulk storage. Study of propagation circuits indicates that reasonable field access memory design objectives are (1) in-plane field frequency, 0.1–10 MHz; (2) in-plane field, 10–30 Oe; (3) storage density, 1.5–10 megabits/in.2; (4) bits/chip, 10 000–100 000.

The epitaxy of zinc sulphide on silicon

The epitaxy of zinc sulphide films on silicon has been studied by means of X-ray and electron diffraction and by scanning electron microscopy. Results have shown that due to the nature of the stacking of atoms, planar defects will predominate in such a sphalerite structure material; this is similar to the results of Pashley and Stowell on face centred cubic metals. Such defects have been shown to be more prevalent on (111) and (110) orientations, compared with the (100) orientation which gave the best epitaxial single crystal films. These results agree with other work from this laboratory on the epitaxy of zinc selenide on germanium and silicon.

Mechanisms of Stress Relief in Thin Films

The stress required to form a dislocation loop of the size of a grain has been calculated for cases where the loop forms within a grain, at a grain boundary, and in grains adjacent to another grain where a loop is already present. It is shown that in typical polycrystalline films this value of the stress is comparable to the observed stresses in films before plastic flow sets in. In the case of single crystal epitaxial films with a high grown-in dislocation density the plastic strain realizable is shown on the basis of a simple model to be a few percent. The model is based on a simple nearest neighbor dislocation interaction and is shown to explain the tensile behavior of thin single crystal films.

Surface Structure of Clean Au (100) and Ag (100) Surfaces

The proposal that reconstructed phases may exist for the clean (100) surfaces of some fcc metals is considered in terms of results obtained from low-energy electron-diffraction studies of epitaxial single-crystal films of silver and gold grown in ultrahigh vacuum (1\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ Torr). The purpose of this paper is to show that the experimentally observed (1\ifmmode\times\else\texttimes\fi{}5) structure on the Au(100) surface and the (1\ifmmode\times\else\texttimes\fi{}1) structure on the Ag (100) surface are characteristic of the clean surface, and to suggest a possible atomic structure for the reconstructed Au(100) surface. The evidence from the epitaxial film studies indicates the occurrence of a thin hexagonal layer of pure gold on the (100) substrate rather than an impurity-stabilized surface layer of hexagonal symmetry, of some unknown substance. It is suggested that the interfacial energy between a thin hexagonal layer and the nonreconstructed substrate may be the determining factor in the occurrence of reconstruction on the (100) surface of fcc metals.