A self-consistent rate equation (RE) approach to submonolayer growth on a one-dimensional surface is presented. This approach explicitly takes into account the existence of gaps between clusters and can successfully predict the coverage dependence of the average densities of monomers N1, and clusters, N. It also implies an unusual dependence for the monomer-monomer capture number σ1 as a function of monomer density. To obtain the island size-distribution, a second set of mean-field equations is used describing the evolution of the size-dependent capture zones and leading to explicit size- and coverage-dependent capture numbers. The solution of this fully self-consistent RE approach is then compared with kinetic Monte Carlo results

The effects of various island and mound relaxation mechanisms on the mound morphology and asymptotic mound coarsening exponent n are investigated for growth on fcc/bcc(001) and fcc (111) metal surfaces. While the strength of the diffusion bias (due for example to an Ehrlich-Schwoebel step barrier) affects the crossover time, the presence or absence of corner diffusion is found to play a crucial role in determining the asymptotic value of the coarsening exponent. In the absence of island-relaxation or in the case of island-relaxation without rapid corner diffusion the asymptotic exponent is found to satisfy n ≃ 1/4. However, when rapid corner-diffusion is allowed, the coarsening exponent is found to approach 1/3. For the case of reversible island growth a strong step-barrier leads to an effective corner diffusion so that a growth exponent of either 1/4 or 1/3 may be observed depending on the strength of the step-barrier. These results appear to account for recent experimental observations of a large coarsening exponent (n ≃ 0.33) in epitaxial growth of Rh/Rh(111) at high temperature as well as of a smaller coarsening exponent (n ≃ 1/4) observed in epitaxial growth of Fe/Fe(001) and Cu/Cu(001). An explanation for these results is also presented in terms of the effects of corner diffusion on the surface current and mound morphology.

Ostwald ripening, early stage and late stage coalescence growth are well–characterized, fundamental late–stage processes in the phase separation of thin film deposits on surfaces. These processes have recently been studied in respect to ordering of the clustered phase. While late stage coalescence growth is associated with random positions of the growing clusters, partial ordering is observed for early stage coalescence and ripening

To obtain even higher order of clustering, additional physical driving forces must be included in the process. Two examples are discussed, one utilizing vertical correlation of clusters in super-lattice growth of coherent Stranski–Krastanov structures (coalescence based structures) and a novel concept based on preferential secondary clustering based on ripening morphologies.

Solid surfaces have many lattice steps. In epitaxy, aggregation of deposited atoms into islands or clusters during their diffusing can create many additional atomic steps. We study the effects of lattice steps on epitaxial growth in two aspects: 1. Movement of atoms across the step edge: a series of field ion microscope experiments reveal the importance of reflective and trapping properties of steps, and provide quantitative information that helps explain various growth modes observed in homoepitaxial growth. 2. Diffusion along the step edge: a number of field ion microscope experiments are done to determine diffusion parameters of a ledge atom along the step edge, and to derive the potential-energy diagram along different diffusion paths that helps explain the growth morphology. During growth, an atom undergoes a number of elementary atomic processes. Each process is characterized by a few energy parameters in bonding and diffusion. The integrated effect of all of these processes determines the growth process. We provide reliable experimental data and find the temperature ranges where various atomic processes are important

We demonstrate that for surfaces that have a nonzero Schwoebel barrier, the application of an ac field parallel to the surface will induce a net electromigration current. Most important, the direction of the net current will be always downhill; i.e. it will point in the step-down direction. The magnitude of this equilibrium current is calculated analytically, and compared with Monte Carlo simulations. A downhill current is known to smooth the surface, thus we suggest that the application of ac fields during annealing might aid the smoothing process and during growth it has the potential to slow or eliminate the Schwoebel barrier induced mound formation

The codeposition of Pb during Si (111) molecular beam homoepitaxy leads to high-quality crystalline films at temperatures for which films deposited on bare Si (111) are amorphous. Like other growth mediating elements-- commonly called surfactants-- Pb segregates to the film surface. Ion channeling and transmission electron microscopy reveal nearly defect-free epitaxy for a Pb coverage of one monolayer and temperatures as low as 310 °C. We have deposited films up to 1000 Å in thickness with no indication that this is an upper limit for high-quality epitaxy. However, a decrease in the Pb coverage during growth by only one tenth of a monolayer leads to highly defective films at these temperatures. The codeposition of both As and Pb results in a striking enhancement of the film quality as well. In this case, while the Pb again segregates to the film surface, the As is incorporated into the film with no apparent segregation. Lead-mediated Si epitaxy on As-terminated Si (111) produces high-quality films in which the As remains buried at the substrate-film interface. These results show Pb-mediated Si (111) homoepitaxy to be a promising strategy for the synthesis of layered structures having abrupt nanoscale dopant profiles

Nucleation and growth of metal clusters at defect sites is discussed in terms of rate equation models, which are applied to the cases of Pd and Ag on MgO(001) and NaCl(001) surfaces. Pd/MgO has been studied experimentally by variable temperature atomic force microscopy (AFM). The island density of Pd on Ar-cleaved surfaces was determined in-situ by AFM for a wide range of deposition temperature and flux, and stays constant over a remarkably wide range of parameters; for a particular flux, this plateau extends from 200 K ≤ T ≤ 600 K, but at higher temperatures the density decreases. The range of energies for defect trapping, adsorption, surface diffusion and pair binding are deduced, and compared with earlier data for Ag on NaCl, and with recent calculations for these metals on both NaCl and MgO

Using Scanning Tunneling Microscopy(STM) and X-ray diffraction(XRD), we have studied the development of surface roughness on Au(111) during 500eV Ar+ ion irradiation at different angles. During normal incidence erosion the surface roughens and pattern formation occurs. The surface morphology is a mixture of mounds and pits superimposed onto a larger structure of channels and valleys. The characteristic spacing between features grows with a power law behavior t27, where t is the amount of time the sample was irradiated, in agreement with previous measurements[l]. At glancing angles, erosion proceeds smoothly, but not in layer-by-layer fashion. Finally, a combination of glancing angle and normal incidence erosion is used to create a rippled morphology

Epitaxial InP(100)-films were prepared with TBP (tertiarybutylphosphine) and TMIn (trimethylindium) as precursors in a commercial MOCVD reactor. During growth, the V-III-ratio and TBP partial pressure were varied between 50 and 1 and possible changes of the surface structure monitored with the corresponding RAS (reflectance anisotropy spectroscopy) signal based on a correlation established with corresponding LEED measurements. Bulk properties of these films were investigated ex-situ with photoluminescence at 2 K, showing no noticeable difference between the samples. The MOCVD apparatus was modified to facilitate transfer of the sample from the MOCVD environment to UIHV in less than 20 seconds (to the 10−9 mbar range). After transfer, the same RA spectrum was recovered also in the critical case of the P-rich, as-grown surface. A corresponding Auger electron spectrum (AES) did not show any trace of contamination. Furthermore, the surface structure was investigated with LEED and STM. The LEED picture shows a clear (2×l)-pattern with a weak twofold symmetry along the [011] direction, STM pictures revealed a disordered surface terminated by P-dimers

Spin dependent tunneling junctions with epitaxially grown underlayers have been investigated to examine the possibility of achieving very flat and uniform barrier layers. Pt/Ni80Fe20 /Fe50Mn50/Ni80Fe20layers were deposited on sapphire (0001) substrates at different temperatures and monitored by in-situ reflection high energy electron diffraction (RHEED). The surface morphology has been found to depend strongly on the growth temperature. X-ray diffraction and magnetic hysteresis loop measurements were also performed to characterize the film structures

We present an investigation on the spatial compositional variation in InGaP layers grown by chemical beam epitaxy (CBE) on pre-patterned substrates. Neighboring regions with 190 meV bandgap discontinuity are observed with the growth at 500°C. The development of laser structures on V-grooves that incorporate these lateral heterostructures is achieved by controlling the growth temperature during growth

A kinetic Monte Carlo model is developed to examine the influence of As/Ga flux ratio on the Ga desorption kinetics during molecular beam epitaxy of (100)-GaAs, based on data reported in desorption mass spectrometry experiments. A good match to experimental results is obtained when a mechanism involving desorption from a physisorbed state is included, in addition to desorption from a chemisorbed state. Analysis of the results revealed that the dependence of the Ga desorption energy on the As/Ga flux ratio, observed in growth experiments, is explained in terms of the component due to desorption from the physisorbed state. The Ga desorption energy associated with the chemisorbed state is independent of the As/Ga flux ratio. These predictions are similar to results reported in a recent study of In desorption during molecular beam epitaxy of InGaAs

Electron cyclotron resonance chemical vapor deposition (ECR-CVD) is used to grow to prepare epitaxial films on Si(100), Si(111), and Si(311) at 325 °C with a growth rate of 10…12 nm/min. On Si(100) up to a layer thickness of more than 300 nm the films exhibit a well defined and smooth interface and a perfectly ordered lattice structure. Beyond a critical thickness of about 500 nm the formation of conically shaped, amorphous regions was observed. At a thickness of 1.6 µm only 10… 15 % of the surface consists of these amorphous cones. On Si(311), Si(111), and Si(011) the critical epitaxial thicknesses hepi depends on the crystallographic orientation of the substrate in the sequence hepi(311) > hepi(111) > hepi(011) with an abrupt change of the film structure from crystalline to amorphous

We investigate the growth mode and the growth mechanisms of selectively grown GaAs nanometer wire structures by metalorganic vapor phase epitaxy (MOVPE). The nanometer wire structures with (111)A or (111)B facet sidewalls are grown on SiNx masked (001) GaAs with line and space pattern openings. As the growth proceeds, the growth rates increase because Ga atoms migrate from SiNx mask surface and (111) facet sidewalls. After the wire formation with triangular cross section is complete, no further growth occurs on the top of the wires, which is called self-limited growth mode. The shape and width of the top area are observed using a scanning electron microscope (SEM) and an atomic force microscope (AFM), and the mechanism of self-limited growth is discussed

We also simulate the growth rate during selective area growth. From the comparison with the experimental results and the simulation, we estimate the amounts of Ga atom migration from SiNx mask area and (111) facet sidewalls to the wire areas.

Finally, we form InAs quantum dots on these GaAs wires, and observe photoluminescence spectra from QDs.

The combination of self-organized growth on high-index substrates with lithographic patterning and atomic hydrogen assistance allows the fabrication of GaAs quantum wires and quantum dots as well as coupled wire-dot arrays with superior structural and electronic properties by molecular beam epitaxy. The selectivity of patterned growth on high-index substrates differs qualitatively from that on low-index ones thus producing quantum wire and quantum dot structures which fulfill the stringent criteria on the geometrical features to be met for useful devices.

Reflectance difference anisotropy (RDA) and low energy electron diffraction (LEED)have been used to study the formation of Ga or Al chains and nanowires on the Si(112) surface. At T > 350°C, the Ga or Al chains form at the step edges by a self-limiting process, while at lower temperatures, Ga or Al nanowires form on the terraces in addition to the chains on the ledges. The process has been tracked in real time from the rapid change of the (2×1) Si(112) reconstruction under subcritical coverage to chain formation leading to a 5×1 reconstruction followed by a 6×1 reconstruction’. During sequential deposition of Ga and Al, we observe (in RDA and AES) that Ga atoms forming the chains can be replaced by Al, indicating a stronger Al-Si bond strength and confirming the chemical sensitivity of the light scattering in RDA. Low temperature depositions (in the 300’C range) are shown to lead to the formation of Al (or Ga) metallic wires on the Si(111) terraces. Continued deposition of less than 10 monolayers at T below 250°C leads to a very anisotropic but patterned Al or Ga structure in registry with the substrate which retains an unexpectedly large polarizability for coverages as thick as 40 ml.

The electrical properties of low temperature MBE grown GaAs (LT-GaAs) in the n-i-n configuration have been studied. The mechanism of current rise in beryllium doped LT-GaAs is found to fit Frenkel-Poole type emission with a barrier height of 0.26 eV. However, this model does not fit undoped LT-GaAs. The breakdown field is considerably higher (up to 5.2* 105 V/cm) for beryllium doped films than undoped films, and depends on both growth temperature and beryllium concentration. Beryllium doping is also found to increase the resistivity of the preannealed films to values > 109 ω-cm.

We demonstrate the first reported use of electron channeling patterns (ECPs) as a response for a statistical design of experiments process-optimization for epitaxial silicon. In an effort to fully characterize the new hot-wire chemical vapor deposition (HWCVD) method of epitaxial growth recently discovered at NREL, a large number of parameters with widely varying values needed to be considered. To accomplish this, we used the statistical design of experiments method. This technique allows one to limit the number of sample points necessary to evaluate a given parameter space. In this work we demonstrate how ECPs can effectively be used to optimize the process space as well as to quickly and economically provide the process engineer with absolutely key information.

This study explores the consequences of structure on the electronic properties of magnetic multilayers. Epitaxial layers of Co and Cu are grown on Cu(100) in a new deposition system that couples sputter-deposition with MBE and contains a wide range of characterization tools, including RHEED, LEED, and Kerr effect. This system can be coupled in situ to spin-polarized, angle-resolved photoemission and to resonant, magnetic X-ray scattering, both employing synchrotron radiation. The interface structure turns out to be critical in determining the coercivity and the presence of quantum well states, which determine oscillatory magnetic coupling.

We report on the room temperature and the low temperature ( 77 K ) study of highly Si doped MBE grown bulk Al.2Ga.8As layers by Photoluminescence ( PL ), Hall, X-Ray and Electrochemical Voltage Profiler ( ECV ) technique. The room temperature PL spectra shows the presence of an asymmetric broad peak in the low energy side whose Full Width at Half Maxima (FWHM) and intensity increases with the doping level. The broad peak has been found to be a combination of two individual peaks, one arising out of the DX center related recombinations and the other due to some Silicon related complex acceptor sites. The low temperature PL also shows a ‘strange peak’ near the Al2Gas8As band edge luminescence peak for wafers grown at 600°C. This peak which increases in intensity at a very rapid rate with falling temperature and shift very rapidly with temperature can be attributed to some AIGaAs growth defect related recombination center, depending on the growth temperature.