The application of Monte Carlo simulations to various epitaxial growth methods is examined from the standpoint of incorporating only those kinetics processes that are required to explain experimental data. A basic model for molecular-beam epitaxy (MBE) is first introduced and some of the features that make it suitable for describing atomic-scale processes are pointed out. Extensions of this model for cases where the atomic constituents of the growing surface are delivered in the form of heteroatomic molecules are then considered. The experimental scenarios that is discussed is the homoepitaxy of GaAs(001) using metalorganic molecular-beam epitaxy (MOMBE) with triethylgallium (TEG) and precursors and using MOCVD with trimethylgallium (TMG). For MOMBE, the comparisons between simulations and experiments are based on reflection high-energy electron diffraction intensities, by analogy with comparisons made for MBE, while for metalorganic chemical vapor deposition (MOCVD) the simulations are compared to in situ glancingincidence x-ray scattering measurements. In both of these cases, the inclusion of a second mobile species to represent the precursor together with various rules for the decomposition of this molecule (in terms of rates and local environments) with be shown to provide a useful starting point for explaining the general trends in the experimental data and for further refinements of the model.

The evolution of surface morphology of molecular-beam-epitaxy-grown GaAs (001) has been studied by scanning tunneling microscope. Images show that in the early stages of deposition the morphology oscillates between one -with twodimensional nucleation and coalescing islands, i.e. flat terraces. After the initial oscillatory regime, the system evolves to a dynamical steady state. This state is characterized by a constant step density. As such, the growth mode can be called a generalized step flow. Comparison with RHEED shows that there is a direct correspondence between the surface step density and the RHEED specular intensity. An increase in step density results in a decrease in specular intensity. Additionally, further deposition beyond 120 monolayers (up to 1450 monolayers) display a slowly increasing surface roughness.

The evolution of surface roughness with increasing thickness of (100) InP layersgrown by metalorganic molecular beam epitaxy has been observed by scanningforce microscopy. The process of roughening gives rise to periodic elongatedfeatures on the surface aligned in the [011] direction, reflecting the surfaceanisotropy. The morphology eventually evolves to a grain-like surface. Theroughening is dependent on both the group III and V flux, and the growthtemperature, indicating that this phenomenon is kinetically controlled by surfacediffusion activation. For each set of parameters chosen for the growth, there is aminimum temperature where smooth, two-dimensional growth can be obtained.Below that temperature the roughening shows two distinct power law regimesdependent on the epitaxial layer thickness.

Hydrogen is shown to influence the surface roughness during low temperature Si MBE. Small partial pressures (1 × 10-7 Torr) of deuterium, introduced during Si growth at 310°C, are sufficient to increase the surface width to ∼30 Å before breakdown of epitaxy. This work is consistent with previous studies of the dependence of epitaxial thickness on hydrogen partial pressure and supports a model in which surface roughening leads to the breakdown of epitaxy.

Compositional ordering has been observed in a wide variety of III/V semiconductor alloys as well as in SiGe alloys. The thermodynamic driving force is now understood in terms of minimization of the microscopic strain energy of the bonds in the solid. However, the mechanism leading to the specific ordered structures formed is only now beginning to be understood. It appears to be intimately related to the physical processes occurring on the surface during epitaxial growth, specifically surface reconstruction and the attachment of atoms at steps and kinks. Thus, an improved understanding the ordering process may lead to a better understanding of the surface processes occurring during epitaxial growth from the vapor.

This paper will review the current understanding of the ordering process, including discussions of the arrangement of atoms on the surface and the nature of surface steps. The emphasis will be on the use of patterned surfaces to investigate and control the ordered structures formed during organometallic vapor phase epitaxial growth of GaInP. Using photolithography and chemical etching, [110]-oriented steps are formed on the (001) GaAs substrate. The direction of motion of these steps determines the specific variant of the Cu-Pt ordered structure (with ordering on (111) planes) formed. The step density at the edge of the groove apparently determines the degree of order. Highly stepped surfaces suppress ordering or lead to small domains of a single variant. When the steps are very shallow, the large domain of the predominant variant is filled with “inclusions” of the second variant. Step edges that are oriented at nearly 160 from (001) form a {511} variant during growth. This facet is observed to grow at the expense of adjacent (001) surfaces and to produce material that is completely disordered.

Growing on intentionally misoriented substrates leads to interesting structures consisting of both large, highly-ordered domains and disordered material. This allows, using cathodoluminescence(CL) imaging, a direct determination of the effect of ordering on the energy band gap. In the GaInP samples studied, the CL images show that the disordered material has a distinct emission pattern consisting of a single, sharp peak at an energy more than 100 meV higher than that observed in the adjacent ordered region.

We have combined Z-contrast imaging and Ge marker layer experiments to study the evolving surface morphology of SixGel-x alloys grown by molecular beam epitaxy (MBE). Surface cusps are seen to arise as the intersection lines between coherent islands. The potential implications of stress concentrations associated with cusps are considered with a view to strain relaxation in the film via dislocation nucleation.

A new technique for Ge/Si heteroepitaxy from the solution, referred to as interfacial energy epitaxy, produces Ge layers with atomically abrupt interfaces to Si and permits monolayer-controlled growth at temperatures up to 937°C. The initial driving force for epitaxy comes from interfacial energy differences between Ge, Si, and the solvent or growth mediator, whose surface free energy has to be smaller than that of Ge. A superheating of the growth solution partly out-balances this driving force, which allows us to minimize the total driving force for epitaxy. Two-dimensional growth results. Subsequent faceting and pseudomorphic island growth manifest additional driving forces for epitaxy, which may be due to interfacial- and strain energy gain.

Two epitaxial growth mechanisms and the resulting defect generation have been examined. The first involves standard growth by molecular beam epitaxy (MBE), while the second employs wet oxidation to form a Ge-rich epilayer from an initially amorphous film. The MBE-grown high Ge content layers evolve by island coalescence, while the oxidationproduced high Ge content layers form by a Ge exchange mechanism below a contamination layer, which results in a more uniform epitaxial layer. Thus, the resulting threading dislocation, stacking fault and twin densities, along with the surface roughness can be quite different. Results also indicate a high misfit dislocation density limited to the Si/SiGe interface and a strain redistribution into the Si substrate for the oxidation-produced epilayers.

We report on the formation of lateral superlattices in short period vertical GaAs/AlAs superlattices. To explain the observed self-organized phase separation, we propose a model of vertical intermixing, driven by the exchange of Ga on the surface with impinging Al atoms. The model correctly describes the formation of lateral superlattices for both integer and fractional monolayer deposition. It also predicts a far-reaching intermixing at GaAs-AlAs interfaces. Insitu RHEED studies of the initial growth stage of both GaAs-AlAs and AlAs-GaAs interfaces support the assumption of an asymmetric exchange at the growing surface and confirm the longrange Ga migration predicted by the model.

The surface kinetics of MBE growth of (100) Ga0.5 Al0.5As are studied theoretically using a stochastic model which is based on master equation with random distribution approximation. The kinetic processes considered are: adsorption and inter- and intra-layer migrations for Ga, Al and As. Both monoatomic and diatomic As molecular species are considered. The model parameters such as the atomic pair interaction energies, migrational requency and activation energy were obtained from available experimental and theoretical data. The surface ordering kinetics are studied as a function of the fluxes (2Å/sec. for cations), flux ratio (1 : 10, 1 : 20 and 1 : 30 for cation to anion) and substrate temperature (775° – 923°K). Degree of ordering was obtained in terms of a short range order (SRO) parameter. The order-disorder temperature defined as the temperature of maximum order (above and below which the order parameter decreases) was obtained for flux ratios of 1 : 10 and 1 : 20. Both As and As2 species were considered. The order-disorder temperature was found to increase as the flux ratio was changed from 1 : 10 to 1 : 30, while the maximum degree of ordering decreased slightly. The results are in good qualitative agreement with experiments. The surface ordering kinetics observed can be described in terms of effective surface migration rates of the cations as follows. Lower temperature and higher flux ratio yield smaller effective surface migration rates for cation, which results in lesser degree of ordering. Beyond the transition temperature, the thermal energy is large enough to thermally randomize the atom pair bonds, thereby decreasing the degree of ordering. The higher transition temperature for higher flux ratios is attributed to lower effective migration rate.

Using reflection electron microscopy (REM), transmission electron microscopy (TEM), and Nomarski optical microscopy we obtained direct evidence that local surface strain-fields, originated from misfit dislocations, are responsible for the formation of morphological crosshatches during molecular beam epitaxy of lattice mismatched InGaAs/GaAs layers. A mechanism is proposed to correlate the formation of the crosshatched patterns with the variation of the growth rate across the epitaxial surface under the perturbation of network shaped strain-fields in the surface.

The band gap of Ga0.5In0.5P is studied as a function of growth temperature, growth rate, and substrate misorientation. As each of these parameters is independently varied the band gap first decreases, then increases, resulting in “U” shaped curves. Each “U” shaped curve shifts if any other growth parameter is varied. The data presented here can be divided into two regions of parameter space. In the low temperature, low substrate misorientation, high growth rate region, the band gap is shown to decrease with increasing growth temperature, decreasing growth rate, and increasing substrate misorientation. In the high temperature, high substrate misorientation, low growth rate region, the opposite trends are observed. The implications of these data on the ordering mechanism are discussed.

We report on a detailed investigation of MBE-grown isotype silicon-doped heterostructures by capacitance/voltage (C/V) technique and deep-level transient spectroscopy (DLTS). A sequence of electrically active defects is found. By depth profiling of the density of the dominant levels it is demonstrated that the corresponding defects are concentrated at the GaAs-on-AlAs (inverted) interface. By comparison with studies on irradiation-induced levels in LPE- or VPE-grown AlGaAs we conclude that the defects at the GaAs/AlAs interface are most probably linked to different charge states of the arsenic vacancy VAs and VAs−ASi pairs.

The evolution of the growth morphology of thin films of InN on (00.1) sapphire and on (00.1) sapphire prenudeated by a layer of AIN have been followed as a function of the thickness of the InN overlayer. The InN thin films and the AIN nucleation layers were deposited by reactive magnetron sputtering and first characterized by X-ray scattering, profilometry, and electrical transport. These AIN-nucleated InN films displayed heteroepitaxial grains, and high Hall mobility -even in the limit of InN overlayer on the order of 20-40Å. In parallel, InN films of varying thickness were grown directly onto (00.1) sapphire. These films showed a mixture of textured and heteroepitaxial grains, and lower Hall mobility. Atomic force and scanning tunneling microscopy studies have focussed on the morphology of the InN films with thicknesses: (a) much smaller than the AIN nucleation layer; and, (b) near the morphological transition that occurs at ∼1μm and has been attributed to the crossover from a 2D to a 3D growth mechanism. Additional correlations of X-ray structural coherence with growth mode are also examined.

The strain relaxation of sputter-deposited epitaxial Fe on Cu(001)/MgO(001) was observed in-situ for coverages of I to 200 equivalent monolayers of Fe. Grazing incidence x-ray scattering (GIXS) with synchrotron radiation allowed the precise determination of the in-plane strain in the Fe film. The highest observed elastic strain for the Fe was -10.3% which is in agreement with the lattice parameter mismatch between Fe and Cu for both (001)- and {211}-oriented growth. In-plane rocking curves revealed a bifurcation of the Fe(110) and Fe(220) peaks which is due to the rotation of islands to reduce strain energy. The angle of rotation of these islands was found to depend upon the amount of strain relaxation that had occurred in each island, in agreement with a simple theory for strain relaxation via the creation of a misfit dislocation network. The absence of Fe(200) intensity at small Fe thicknesses, coupled with out-of-plane symmetric and pole figure scans, suggest that Fe islands are tilted out of the plane of the sample about the Fe<110> axes by an angle consistent with Fe{211}-oriented growth. At larger thicknesses Fe(001) growth becomes dominant.

We report the structural characterization of the 3-D relaxation morphology of In0.4Ga0.6As grown on a step-graded InxGa1-xAs buffer layer on GaAs. Scanning electron microscopy showed “grooves” spaced on the order of microns running only in the [110] direction. Each groove was observed with cross-sectional transmission electron microscopy to mark the location of a vertical low-angle tilt and/or twist boundary. The veiy rough layer morphology may be the result of island coalescence or severe surface roughness that created the grain boudnaries as the layer grew. Strain relaxation in the In0.4Ga0.6As layer was much reduced in the [101] in-plane direction. The asymmetry in residual in-plane strains in the In0.3Ga0.7AS layer and/or the increased In composition may be responsible for the development of an anisotropic surface roughness. X-ray microanalysis revealed a periodic variation in layer composition which correlated with a fine contrast modulation presumably the result of phase segregation.

The segregation and interdiffusion of In atoms in the GaAs/InAs/GaAs heterostructures were investigated by secondary ion mass spectroscopy. When the 1 ML thick InAs layer was grown in a layer-by-layer growth mode with no dislocations, the segregation of In atoms became marked with the increase of the growth temperature. However, the segregation was observed even at relatively low growth temperature of 400°C in molecular beam epitaxy. It was found that the segregation was markedly enhanced by dislocations near the heterointerface when the thick InAs layers were grown in a three-dimensional island growth mode. The interdiffusion of In atoms toward the growth direction occurred after thermal annealing, which could be assisted by vacancies propagating from the film surface into epilayer. It became apparent that the interdiffusion was effectively suppressed by a thin AlAs layer inserted in the GaAs cap layer.

The lateral periodicity of an InAs quantum dot array in a GaAs matrix is measured in the differential rocking curve by triple crystal diffractometry. The quantum dot array was grown by molecular beam epitaxy of submonolayer InAs films on a terraced (001) GaAs substrate. The x-ray diffraction of the array is described in the limits of the kinematical theory. Both the changes in the scattering factor and the tetragonal deformations due to the InAs quantum dots are taken into account. The lateral periodicity of the array along [100] is 8–11nm dependent on the position of the measured region compared with an average of 10nm obtained from the miscut of the sample. In addition the vertical periodicity of the array is measured by comparison of the double crystal rocking curve with the corresponding simulation in the dynamical approximation. The vertical period of the array along [001] is 26.5nm. The coverage of the submonolayer InAs films estimated from the same measurement is 0.4. The absence of plastic relaxation is confirmed by x-ray topography.

Epitaxial YSi2-x, TbSi2-x, and ErSi2-x. have been grown on (111)Si by solid phase epitaxy in ultrahigh vacuum deposited rare earth (RE) metal thin films on silicon. The evolution of vacancy ordering and defect structure in epitaxial RE silicide thin films on (111)Si have been studied by both conventional and high resolution transmission electron microscopy.

Additional superlattice spots located at 1/3 <2110> in the diffraction pattern of RESi2-x, are attributed to the formation of ordered vacancy in the Si sublattice planes. The splitting of extra diffraction spots is correlated to the formation of an out-of--step structure. Streakings of the split diffraction spots in the diffraction pattern are attributed to the presence of an out-of-step structure with a range of M values. For YSi2-x and ErSi2-x, the M was found to settle down to a constant value after high temperature and/or long time annealing. For TbSi2-x, M is equal to 5 throughout the annealing.

Planar defects in RESi2-x films were analyzed to be stacking faults on {1010} planes with 1/6<1213> displacement vectors. The size and density of stacking faults were found to increase and decrease, respectively, with annealing temperature and/or annealing time.

In this paper we present the TEM observations carried out on In0.52Al0.48As layers grown on InP at Tg+570°C. Plane view observations along the (100) zone axis show the existence of two types of contrast irregularity, with dark-bright fringes along the <010> directions and extinction for g +040 type reflections. One of these structures has been clearly related to precipitates at the lnAlAs/InP interface. The other, presents stacking fault-like fringes on the (100) plane, and the analysis of its traces on both (100) and (011) planes are presented. Despite the fact that its appearance resembles that of the structure linked to the precipitates, we will show that they are different phenomena and may even coexist.