RHEED is an important method for the in situ characterization of surfaces. Until recently, this characterization has not used the intensities of RHEED reflections. Improved methods of calculation have made it possible to simulate RHEED patterns from bulk-terminated, reconstructed and stepped surfaces. From the comparison between simulated and experimental patterns, it is now possible to refine the positions of atoms in surfaces and to determine the density of steps on surfaces (well almost).

We have studied the reentrant growth in kinetic thin-film deposition on stepped surfaces using a Monte Carlo simulation. The results show that the reentrant oscillation of two dimensional nucleation growth occurs as a result of the variation of surface diffusion length with deposition temperature, and that it is a natural phenomenon in kinetic thin-film epitaxy on a substrate with a permanent step source.

RHEED pattern of SiC layers on both (100) and (111)Si grown by carbonization were studied. Different deviations from the single crystalline structure were found ranging from twinning up to changes in the orientation and textured growth. Special attention was drawn on lattice relaxation and morphology evolution during the growth of the formed SiC. Relationships between the occurrence of typical RHEED pattern and the morphology and process parameters are presented.

Single-crystal GaAs films were grown on SI (100) GaAs at substrate temperatures below 200 °C by using ionized source beam epitaxy. The correlation between the properties of the films and the growth parameters, in particular, the substrate temperature, the amount of As-source beam ionization, and the acceleration voltage of the As beam was investigated to elucidate the possible benefits of source beam ionization and acceleration on low-temperature thin film growth. The use of ionized and accelerated As-source beam greatly improved the quality of the low-temperature grown GaAs film. The surface morphology, crystallinity, and micro structure of the low temperature grown GaAs films were evaluated using in situ reflection high energy electron diffraction, double crystal X-ray diffraction, and cross section transmission electron microscopy.

MnAs thin films grown on GaAs (001) substrates by molecular beam epitaxy have been studied by grazing incidence x-ray scattering (GIXS), x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS). Microstructures in films prepared with different first-layer growth conditions (template effects) are compared in terms of the interfacial roughness, lattice constants, epilayer thickness, local environment surrounding the Mn atoms, coordination number, and local disorder. The template effects are found to cause significant differences in the local structures and crystallinity of MnAs epitaxial layers.

The nucleation and growth of islands in the early stages of epitaxial growth is studied with kinetic Monte Carlo Simulations and self-consistent mean field rate equations. Specifically, adatom exchange and irreversible dimer formation are allowed to compete equally as the origin of two-dimensional islands. The island size distribution and number density are found to satisfy a dynamic crossover scaling form. The critical island size evolves from one to zero with increasing temperature, decreasing flux, and increasing coverage.

Kinetic model of MBE growth on vicinal surface is investigated. The model includes step propagation, nucleation and growth of islands on the terraces and Schwoebel barrier at descending step edges as -well. By numerical solution of kinetic rate equations for growth on stepped surface, adatom and island density profiles across a terrace are obtained. With using simple criterion for growth mode transition the "phase diagram" of growth modes in parametric space γ–β is constructed, γ∼J/D and β∼tan-2φ, where J is the atomic flux, D is the surface diffusion coefficient and φ is the substrate miscut angle. The transition curve in the γ–β plane separating step flow mode region from the mixed (step-flow+nucleation) growth mode region is well describded by a simple equation γ=A/β3 where constant A=10 and 100 with and without Schwoebel effect. The relations for critical terrace width (miscut angle) and transition temperature are derived and it is shown that these relations are in fairly well agreement with available experimental data on the MBE growth of GaAs.

We have investigated the kinetics of islanding during heteroepitaxy using a solid-on-solid Monte Carlo (SOS-MC) simulation. We simulate deposition by randomly depositing atoms onto a square grid with periodic boundary conditions. Arrhenius surface diffusion kinetics are dependent on the sum of a surface energy barrier (Ed) and the number of nearest neighbors multiplied by an adatom interaction strength (Eb). We confine growth to the first layer above the simple cubic substrate and investigate coverages < 1/2 monolayer. We monitor the evolution of film microstructure by producing island size distributions and plots which compare a cluster's area to perimeter ratio with that of a circle. We find that our simulation qualitatively correlates with results of classical film nucleation theory. A simple model is used to demonstrate the existence of a 'probabilistic nucleation barrier'.

Island size distributions have been derived from scanning tunneling microscope (STM) images of Ni deposited on cleaved GaAs(110) at room temperature and above. For submonolayer coverages, this system forms 3-dimensional (3-D) reacted islands with the degree of reaction dependent upon the growth temperature. As has been found for other systems, the average island size (sαυ) increases with temperature. The high temperature data (∼ 150° C) shows two distinct island types, each with substantially different average size. The island size distributions have maxima at the smallest island sizes. For different coverages, plots of the area-normalized island size distributions versus the scaled variable s/sαυ show significant differences. However, above a cutoff value for s/sαυ the distributions can be renormalized to fall on a common curve. These characteristics and direct atomic-scale evidence are consistent with nucleation of islands via adatom-substrate exchange, but the temperature dependence of the total island density appears to be inconsistent with this being the only first-order rate process taking place.

In the past simulations of epitaxial growth have used solid-on-solid (SOS) models to simulate the crystalline structure of both the substrate and the growing crystal. These models have produced results in the early stages of growth in good agreement with experiments for a number of different quantities, including the island density and the island size distribution. For multilayer growth, however, there exists a competition between microscopic effects such as the Ehrlich-Schwoebel step barrier and the crystalline microstructure. Therefore, the crystal structure and geometry are important in determining the dynamics and evolution of epitaxial structure and morphology. We present the results of large-scale realistic kinetic Monte-Carlo simulations of multilayer epitaxial growth on fcc(100) and bcc(100) surfaces. The influence of crystal structure on the formation and coarsening of mounds and facets is discussed. We also discuss and compare our results with recent experiments.

We present a dynamical version of the Smart Monte Carlo method to model the diffusion dynamics of a metal atom on a metal surface. This method, in conjunction with umbrella sampling, can be used to simulate the dynamics of metal thin film growth, including all relevant atomic-scale phenomenon, over long time scales, characteristic of experimental studies. To demonstrate the accuracy of this method we simulate the dynamics of Rh on Rh(111) and Cu on Cu(100). Interatomic forces are modeled with Lennard-Jones and Corrective-Effective-Medium potentials for the Rh and Cu systems, respectively. We show that this new simulation method correctly reproduces the diffusion dynamics and, with some modification, allows us to reach experimental time scales.

(1+1)-dimensional stochastic simulations were performed representing elementary processes underlying chemical vapor deposition of diamond films. The results exhibit different growth regimes, depending on the values assigned to kinetic rates, and generally support the critical role of surface migration suggested earlier for the growth of diamond.

We model kinetic roughening during Fe(100) homoepitaxy, where the formation of mounds with selected slope has been observed. Our model incorporates irreversible nucleation and growth of two-dimensional square islands in each layer, and a step-edge barrier to diffusive downward transport (which exceeds the barrier, Ed, to terrace diffusion by ESch). We estimate that ESch≈45meV compared with Ed≈450meV. To reproduce observed behavior, it is also essential for the model to incorporate "downward funneling" of depositing atoms to four-fold hollow adsorption sites, as this controls slope selection. Finally, we discuss model predictions for the non-monotonic temperature dependence of kinetic roughening.

Simulated kinematic antiphase RHEED and HRLEED profiles are calculated for a model of Fe/Fe(100) deposition in order to clarify the interpretation of diffraction profiles in recent experiments on Fe/Fe(100) growth. Similar calculations are also presented for a self-affine surface. While self-affine surfaces do not exhibit a characteristic RHEED peak, in the case of surfaces with a typical length scale, the simulated RHEED profile exhibits a peak corresponding to the typical feature size, in agreement with recent experiments. The existence of this peak appears to be due to the large amount of shadowing present in low-angle RHEED which limits the amount of destructive interference between layers. In contrast, simulated HRLEED profiles exhibit an invariant profile for both self-affine and mound-like surface morphologies. The disappearance of the peak in HRLEED for surfaces which have large mound structures is explained in terms of the antiphase condition and the range of variation of terrace sizes and provides an alternative explanation for the HRLEED results observed in the experiment of Ref. 9.

The growth morphology of Ag on GaAs (110) surfaces, at low coverages, is investigated with Monte Carlo simulations using a solid-on-solid model. Experimentally Ag deposited at room temperature forms 3D isotropic islands and forms needle-like islands elongated along the <110> direction when deposited at 250°C. Preliminary simulation results using 2D island growth model indicated that the elongation of islands at 250°C deposition is due to anisotropic surface diffusion and nearest-neighbor interactions along the <100> and <110> directions. The island morphologies obtained using a 3D island growth model are in good agreement with experimentally observed morphologies.

This work aims to provide a systematic approach for deriving desorption mechanisms on semiconductor surfaces from a coupling of temperature programmed desorption (TPD) experiments and Monte Carlo (MC) simulations. MC simulations are used to evaluate different desorption schemes to identify mechanisms consistent with experimental results. Effects of nearest neighbor interactions, island formation, and surface reconstructions are quantified through the simulations. Methyl desorption from Ga-rich GaAs is used as a case study to illustrate the MC procedure for interpretation of TPD spectra.

Thin heteroepitaxial films of Si1-x-yGexCy have been grown on (100)Si substrates using atmospheric pressure chemical vapor deposition at 550 and 700°C. The crystallinity, composition and microstructure of the SiGeC films were characterized using Rutherford backscattering spectrometry (ion channeling), secondary-ion-mass-spectrometry and cross-sectional transmission electron microscopy. SiGeC films with up to 2% C were grown at 700°C with good crystallinity and very few interracial defects, while misfit dislocations at the SiGe/Si interface were observed for SiGe films grown under the same conditions. This difference indicates that the presence of carbon in the SiGe matrix increases the critical thickness of the grown layers. SiGeC thin films (>110 nm) with up to 3.5% C were grown at 550°C with good crystallinity. The crystallinity of the films grown at lower temperature (550°C) was less sensitive to the flow rate of the C source (C2H4), which enabled growth of single crystal SiGeC films with higher C content.

We report on the morphology of heavily phosphorous doped silicon films grown by ultra high vacuum chemical vapor deposition at temperatures of ∼550° C. The effects of PH3 on epitaxial films have been examined for silicon deposited using SiH4 and Si2H6. It is found that films grown using silane experience an increase in surface roughness with increasing phosphine partial pressure. AFM and RHEED studies indicate 3-D growth. As epitaxy progresses, it is believed that phosphorus segregation on the growing film surface greatly diminishes the adsorption and surface mobility of the silicon bearing species. Initial Si deposition results in a pitted surface, but as growth advances and the phosphorus coverage increases, growth within the pits decreases the surface roughness. In contrast to SiH4, it is found that Si2H6 provides excellent quality, smooth films even at high PH3 partial pressures.

A novel in situ sample cleavage technique has been developed for fabricating specimens for cross-sectional scanning tunneling microscopy (XSTM) applications. This technique can be easily adapted to any ultrahigh vacuum (UHV) STM that has a coarse motion capability. A conducting diamond STM tip is used to create micron long scratches on Ge/GaAs or GaAs {001 }-type surfaces. These {001} surfaces are imaged with STM to observe scratch characteristics, and GaAs samples are cleaved to reveal {110}-type faces. Atomic resolution images of {110}-type GaAs surfaces are readily and reproducibly obtained.

The growth of thin Pd, Ni, Fe and Ti films on Al(110) surfaces has been studied using high-energy ion scattering (HEIS), x-ray photoemission spectroscopy and photoelectron diffraction techniques. Of these four metals, only Ti grows as an epitaxial overlayer, while the other metals mix with the substrate to form surface alloys. In the HEIS experiments the backscattered ion yield from Al surface atoms is measured as a function of metal coverage on the Al surface. A decrease in the Al scattering is observed for Ti deposition while the other metals result in increased Al scattering, attributed to alloy formation. An explanation for the exceptional growth behavior of Ti on Al is provided using a model of surface strain associated with aluminide formation.