This paper investigates the defect formation at the epi/substrate interface and epitaxial layers due to an improper in–situ Ar or Ar/H2 plasma cleaning at 500–800 °C Deposition process was carried out immediately after the in–situ cleaning process by ultralow pressure chemical vapor deposition process (ULPCVD) from SiH4/H2. Characteristics of the defects and their relationship with damage or impurity contaminations at the interface are presented. Finally, an optimum cleaning condition which ensures high quality epitaxial growth is addressed.

In situ etching of native Si02 by Ar+ ion bombardment before metal sputter deposition can increase the contact resistance of the metal-semiconductor contact. This is commonly attributed to surface contamination produced by various mechanisms or to etch-induced surface damage. In this paper, in order to elucidate the cause of the increase of contact resistance, we have studied (Al-Si)/n+Si contacts prepared by various treatments of the Si surface. We attribute the higher postalloy contact resistance of the sputter etched contacts to the existence of an Al doped layer which formation was induced by the preexisting disordered layer created by the Ar+ ion bombardment.

Lattice matched ScxEr1-xAs (ScErAs) was grown on GaAs by MBE followed by a GaAs overlayer. The overgrowth of GaAs on ScErAs has been studied by Reflection High Energy Electron Diffraction (RHEED), Low Energy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES), Nomarskii-interference microscopy and Transmission Electron Microscopy (TEM). In this study substrate temperature and crystal orientation have been varied. For GaAs growth on (100)ScErAs there is a strong tendency for island formation and three dimensional (3D) growth. For high substrate temperatures (>500 °C) and for moderate growth rates (10 ML/min) the growth can be described by the Volmer-Weber mode. For lower substrate temperatures we observe that one monolayer of GaAs on ScErAs is metastable. This monolayer shows a (3×1)/(1×3) surface reconstruction. The deposition of more than one monolayer, irrespective of substrate temperature, or the raising of the substrate temperature induces island growth. The metastable reconstructed surface layer of GaAs then partly dissolves into the islands. The strong tendency for 3D growth observed here is very similar to that seen in the growth on ErAs which is not lattice matched to GaAs. This observation demonstrates the significance of electronic bonding mismatch over lattice mismatch for heteroepitaxy between materials with ionic and covalent bonding character. Growth on {111}-polar surfaces yields smoother layers and a stronger tendency for 2D growth.

A surface phase transition associated with a surface miscibility gap has been observed on the (111) surface of Cu-Ag alloys both in computer simulations and in experimental measurements of surface composition. This transition is characterized by an abrupt change in surface composition associated with changes in either bulk composition or temperature.The simulations have revealed that the transition from a Cu-rich to a Ag-rich surface phase is accompanied by interesting changes in surface structure. The experiments show that the surface critical temperature lies somewhere between 505 and 560°C.

We report on the epitaxial growth of superconducting molybdenum films on sapphire substrates. These films are to be etched into arrays of isolated cylinders, each 1–5μm in diameter. When placed in a magnetic field and biased at 0.95 Tc(H), the flux movement associated with their bolometric response to the energy deposited when radiation is absorbed will provide the basis of a gamma-ray detector.

The films were prepared by UHV sputter deposition at temperatures between 650° and 840°C. Besides standard XRD analysis the films were examined by TEM. An epitaxy orientation relationship with sapphire was found similar to that observed for niobium. Electrical conductivity measurements were made as a function of temperature down to Tc, the superconducting transition temperature, which ranged from below 0.35K to above 0.8K for films with a high room temperature resistance ratio (e.g. 300 in a 0.9pjn thick film). Results from a range of films will be presented and their Tc’s discussed.

We investigate the ion beam damage of clean Au (001) single crystals prepared under standard surface science techniques using sputter - anneal cycles. Under initial ion milling conditions using 4 keV Xe ions a significant amount of Xe was implanted into the bulk of the crystal. After a short period of time a Xe super structure developed which yielded 12 Å moire fringes under bright field imaging conditions. With a short anneal the implanted Xe concentration was reduced to the detection limit of Parallel Electron Energy Loss Spectroscopy (PEELS). With extended annealing, the bulk point defect concentration slowly decayed, independent of the surface reconstruction.

The evolution of the microstructure of sol-gel derived LiNbO3 thin films was investigated to understand the growth of epitaxial films. LiNbO3 films were prepared from a precursor solution of lithium ethoxide and niobium pentaethoxide. Prehydrolysis promoted the development of polycrys-talline LiNbO3 films, whereas nonhydrolysis produced solid-state epitaxial growth of LiNbO3 films on sapphire substrates. Although the films looked smooth after annealing at 400°C, the morphology of the films changed, depending on substrates and precursors, due to grain growth at high annealing temperature. Prehydrolysis of the alkoxides caused a decrease in the temperature at which grain growth occurred, whereas the film prepared from the nonhydrolyzed precursor on a sapphire substrate showed denser texture and contained abnormally large domains that appeared to be single phase.

Crystallographic structure and valence state of CeO2 and Nd2-O3 films deposited by laser MBE on Si substrates were investigated by reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS). In contrast with epitaxial growth of CeO2 (111) and Nd2O3(111) on Si (111), epitaxial films were not obtained on Si(001). Partially reduced mixed valence (4+ and 3+) Ce was indicated to exist by XPS in the cerium oxide film within 2nm from the interface with Si. Beyond this transition layer, two-dimensional growth of CeO2 film on Si(111) was verified from in situ RHEED and as well as on Si(001) from XPS measurements.

Domain boundaries have been characterized by transmission electron microscopy in single crystal [0001] α-Al2O3 epitactically regrown after being amorphized by stoichiometric ion implantation. The domains are facetted on {1120} and have dislocation-like features at facet intersections. End-of-range dislocation loops on (0001) appear to be the nucleation site for the domains. Diffraction contrast, high resolution imaging, and convergent beam electron diffraction techniques showed that two types of domains are present which involve cation stacking sequences which are out of phase with the matrix as a result of translation along and/or inversion of [0001]. The non-inverted regions can be described as anti-phase domains, whereas those with [0001] inverted also have a basal twin character.

Zinc oxide films have been deposited from dimethyl zinc and oxygen in an atmospheric pressure laminar flow reactor at temperatures ranging from 300°C to 450°C. Highly oriented, conductive and transparent films were obtained at temperatures above 400°C by doping the films with fluorine. The crystallite sizes increase with increasing deposition temperature. From electron microprobe analysis, the doped films usually contained 0.5% to 2% fluorine atoms. Hall coefficient and resistance measurements at room temperature gave electron concentrations above 1020cm−3 and resistivities around 10−3 Ωcm. The doped films had mobilities varying from 20 to 40 cm2/V-s depending on the deposition temperature and fluorine concentration. These are the highest mobilities reported for zinc oxide films. The experimental results were then compared with those obtained from a simple resistivity network model which includes the effects of impurity and grain boundary scattering. Films with a sheet resistance of 5 Ω/square have visible absorption of about 5 to 10%. These properties are very suitable for applications as transparent electrodes for flat-panel displays and other electro-optical devices.

In the present study epitaxial Ni(001) films have been grown on natural C(001) substrates (type la and Ha) and homoepitaxial C(001) films. Two deposition techniques including electron-beam evaporation of Ni in a molecular beam epitaxy (MBE) system and evaporation of Ni from a resistively heated tungsten filament have been employed. As evidenced by scanning electron microscopy (SEM), the Ni films deposited by electron-beam evaporation were found to replicate the very fine, unidirectional scratches present on the as polished C(001) substrates. Indeed, the coverage and uniformity of the deposited films would imply a two-dimensional (2-D) growth mode. In comparison, the thermal evaporation of Ni on C(001) substrates results in a highly textured and faceted surface morphology indicative of three-dimensional (3–D) nucleation and growth. Moreover, Rutherford backscattering/channeling measurements have demonstrated that the Ni(001) films deposited by electron-beam evaporation are of superior crystalline quality. Differences in the observed microstructure and apparent growth modes of the epitaxial Ni(001) films have been attributed to the presence of oxygen incorporation in those layers deposited by thermal evaporation.

In order to realize a thin film of organic single crystals, we have been investigating fabrication process using vapour deposition technique. Up to now, highly oriented thin films of 2-methyl-4-nitroaniline(MNA) and 4-(N,N-dimethylamino)-3-acetamidonitrobenzene(DAN), both of which are promising organic materials for nonlinear optical devices, could be fabricated on a buffed polyimide and on a thermally oxidized silicon wafer, respectively. In the case of MNA films, a series of results by X-ray diffraction and by SEM observation showed weak two-dimensional characteristics suggesting the existence of topographic effects and/or of interaction between MNA molecules and molecular moieties of polyimide substrate. Small optical transmittance of both MNA and DAN thin films are explained in terms of light scattering by grain boundaries and surface roughness.

GaAs layers grown by solid phase epitaxy on (001) Si substrate were subjected to post-growth rapid thermal anneal (RTA) at 700, 800, and 900°C for 10s in a N2 atmosphere. Rutherford backscattering/channeling showed a substantial improvement in crystalline quality of GaAs epilayer after RTA at 800°C. After RTA at 900°C for 10s, stacking faults (and/or microtwins) were eliminated entirely, and the dislocation densities in both the interface region and the film interior were reduced. High-resolution transmission electron micrographs showed a significant change in misfit dislocation structure at the interface after RTA; namely, the 90° pure edge and 60° misfit dislocations were transformed to an evenly distributed array of 90° dislocations at the interface.

Metalization patterns of micron size were deposited chemically on GaAs wafers with no litography masks by means of controlled laminar flow of liquid NaOCl. Iron used for metalization was dissolved in NaOCl wafer solution. To interrupt the continuous deposition of metal on semiconductor surface, the acrylic polymer was also dissolved in the liquid. Iron deposition appears to follow given crystalographic direction <110> creating a set of parallel lines in <110> direction. Spacing between the lines and width of the metallic lines are controlled by the temperature of the process, speed of liquid flow and percentage of polymer present in the solution.

Layered silicon/silicon nitride structures were fabricated on (100) Si with 0.1 mTorr of N2 background pressure. Evaporated Si (PVD) layers were alternated with layers grown by simultaneous nitrogen ion bombardment and Si evaporation (IBAD). The ion to vapor flux ratios were chosen to yield stoichiometric Si3N4 (XN=0.57) at 150, 500, 1000 and 1500 eV and varied at a constant energy of 500 eV to yield sub- and superstoichiometric Si1-xNx. The microstructures were examined by cross-sectional and plan-view TEM; composition of the layers was deteiTnined by RBS. Films grown at low substrate temperatures were amorphous. Stoichiometric and superstoichiometric compositions showed a cellular (5 nm) structure in the amorphous IBAD layers. In addition, the IBAD Si1-xNx layers showed variations in contrast parallel to the substrate interface, indicative of compositional fluctuations on a scale of <20 nm. The IBAD layers were dense, but the PVD-Si layers contained voids that were aligned with the direction of the impingement of the evaporant on the substrate surface. A high substrate temperature (750°C) yielded polycrystalline Si layers and phase-ordering in the Si1-xNx layers.

In this paper we examine the role of strain and growth kinetics on the growth modes in pseudomorphic growth. Regimes below critical thickness and above critical thickness are examined. Based on atomistic modelling and in-situ RHEED and STM studies we show that a competition between surface chemical energy and strain energy is shown to lead to 3-dimensional blend mode for high strain pseudomorphy. Consequences for dislocation generation are discussed.

Growth onto vicinal substrates causes 60° misfit dislocations to adopt line directions away from <110> in order for them to maintain their presence within the substrate to strained layer interface. Observations show that for the growth of an on-axis [001]wafer the dislocations have a line direction, within measurement error, exactly [110] or [-110] and two sets of orthogonal dislocations are generated. When grown onto a wafer that is cut off-axis toward [010] four sets of dislocations are generated. The two sets of dislocations in each direction converge to form low angle intersections from which edge dislocations are formed. These edge dislocations can become very long by the glide out of the interface plane of the component 60° dislocations. This ‘zipping-up’ to form the edge components only occurs in one direction from the low angle point of intersection and the edge segments are exclusively generated in the buffer layer. Their density and penetration are a function of thickness and composition of the mismatched epilayer. The mechanisms by which the dislocations adopt line directions away from <110> and why they zip-up from the intersection in only one direction are discussed.

The contrast of misfit dislocations in an InGaAs layer, close to the critical thickness and capped with GaAs grown by MBE on a (001) oriented GaAs substrate has been investigated by double axis synchrotron X-radiation topography. The layer thickness variation as a function of position has been measured to a precision of 1A by matching interference fringes observed in the 004 symmetric reflection double crystal rocking curves with simulations. The misfit dislocation density is highly anisotropic, varying from zero to a high value with increasing thickness. The contrast of the dislocations in the 004, 224 and 044 reflections has been examined in detail. All of the long dislocation segments characterized were 60° in character with ½<110> Burgers vectors inclined to the specimen surface. No dislocations were found which did not appear to be of this type. A surprising difference in contrast of the background in the 224 and 224 reflections is discussed.

Relaxation in a 3μm epitaxial layer of GaAsSb on GaAs, a 1μm layer of InGaAs on InP and an InGaAs superlattice on InP has been investigated by double crystal X-ray diffractometry and double crystal X-ray synchrotron topography and found to be asymmetric. The origins of assymetric relaxation are discussed and the sensitivity of diffractometry and topography to the detection of layer relaxation compared.

We have studied the initial stages of highly mismatched InxGa1-x As growth on GaAs (100) by transmission electron microscopy (TEM). We find direct evidence of (i) deformation in the substrate below each island to depths of about 150 A and (ii) strain relief in the islands at their lateral edges. Growth morphology as a function of growth temperature is studied and it is found that the tendency for islanding for x as high as 0.5 can be supressed to a large extent by a reduction in the growth temperature. We also present results of correlation between TEM determined different growth morphologies (brought about by different growth temperatures ) and the electrical characteristics of AlAs/InxGa1-xAs resonant tunneling diode structures grown on GaAs (100).