We have modified a normal-incidence optical reflectance spectroscopy system to allow rapid switching between the measurement of sample reflectance and sample emission. The resulting optical system is capable of “smart” pyrometry, in which sample emissivity is measured rather than assumed. The emissivity measurement makes use of the principle of detailed balance, which states that for specular, opaque samples, the sum of the emissivity and reflectance at each wavelength is equal to 1. We present data based on multilayer III-V semiconductor structures grown by molecular beam epitaxy, but the optical system would function equally well in any growth or deposition system with optical access to the substrate. The “smart” pyrometry temperatures we measure typically differs from conventional pyrometry by 5 to 10°C, and occasionally as much as 20°C, for multilayer structures of AIGaAs and GaAs. We present details of the optical components and arrangement that minimize the effect of sample wobble and allow the system operator regular visual access to the sample. Calibration techniques for the combined system are also discussed.

“Self-assembled” monolayers of amphiphilic surfactant molecules form spontaneously on solid surfaces by exposure to dilute solutions of the adsorbate molecules. These monolayers are shown to form via a mechanism that includes nucleation, growth, coalescence, etc. of densely- packed submonolayer islands of the long-chain organic molecules. In situ atomic force microscopy experiments allow a quantitative analysis of island nucleation and growth rates as well as determination of the island size distribution as a function of coverage. In the growth regime, the nucleation and growth rates have a power law behavior consistent with a simple point island model of 2D cluster growth. The exponents are consistent with a critical nucleus of two molecules and the 2D diffusion coefficient corresponds to a “hopping time” of about 1 microsecond. In the aggregation regime, the island size distributions are shown to scale with a single evolving length scale in accordance with the dynamical scaling approximation.

The realization of Planar Doped Barrier Diode (PDBD) presented in this paper starts out from the limits of the MBE layer growth technology. The limitations due to the background doping concentration and the diffusion of the n and p type dopants during the epitaxial growth are considered. The next parameter is the height of the potential barrier. The choice of this value depends on the requirements of the application. It must take into consideration the current transport mechanisms and the current limitation appearing at higher bias levels.

An experimental study of the microstructure during formation and evolution of MOCVD-grown In0.6Ga0.4As/GaAs quantum dots (QDs) was undertaken to provide a more thorough understanding of the underlying growth principles. Transmission Electron Microscopy (TEM) was used to examine the evolution of the In0.6Ga0.4As/GaAs system in order to correlate photoluminescence (PL) spectra with structural data. In particular, we have examined the QD size evolution, capped and uncapped, and its possible contribution to the slight QD PL blueshift observed before QD saturation. TEM studies in the QD coalescence regime clarify the microstructural origins of the sharp decrease in QD PL due to large, incoherent islands observed in AFM and TEM images.

Synchrotron x-ray topographs of GaAs epitaxial lateral overgrowth (ELO) samples are made both in transmission and reflection geometries. The topographs show that the bending of the ELO layers is visible in most geometries. A simulation of the topographic images is implemented taking into account only the orientational contrast. Simulated back reflection section topographs are in good agreement with the experimental ones. The shape of the lattice planes in an ELO layer is calculated using the simulation data and compared to the measured surface profile of the same ELO stripe.

Pure Ge epitaxially grown on Si (100) at high temperatures forms typically 100 nm lateral size islands on top of a 3–4 monolayer thick wetting layer. In stacked layers of Ge dots pronounced vertical alignment is observed if the thickness of the Si spacer layers is smaller than about 50 nm. Pregrowth of a small amount of C on Si substrate induces very small 10 nm size Ge quantum dots after deposition of about 2 to 3 monolayers Ge. Photoluminescence (PL) studies indicate a spatially indirect radiative recombination mechanism with the no-phonon line strongly dominating. Strong confinement shift in the 1–2 nm high and 1Onm lateral size dots results in low activation energies of 30 meV, which causes luminescence quenching above 50K.

For large stacked Ge islands with 13 nm thin Si spacer layers we observe a significantly enhanced Ge dot-related PL signal up to room temperature at 1.55μm wave length. This is attributed to a spatially indirect transition between heavy holes confined within the compressively strained Ge dots and two-fold degenerated Δ state electrons in the tensile strained Si between the Ge stacked dots.

Using liquid phase epitaxy from Bi solution in the temperature range 550°–700°C at low growth rates we study the formation of ripples and islands and their interdependence. As main results we find from the dependencies on growth time and temperature that ripples are an instability phenomenon and that islands nucleate thermally activated. Island nucleation on a ripple template (that is, as an instability phenomenon, highly ordered) has huge impact on the achievable order of the islands.

Hut- and dome-shaped islands have been observed during low-pressure vapour phase epitaxy (LPVPE) of Ge on Si(001) at 700°C. The experiments show that a coarsening process occurs in connection with the deposition process, leading to an island height increase with increasing deposition time (total Ge-coverage was kept constant). The shape transition from huts to domes, which takes place after hut clusters have reached a baselength of 80nm, indicates that huts are not a stable configuration. Photoluminescence measurements show a linear correlation between hut cluster density and integrated photoluminescence intensity.

We addressed the initial strain relaxation of symmetric 95 Å period Si0.91Ge0.09/Si heterostructures grown by ultra-high vacuum chemical vapor deposition on vicinal substrates miscut 2.04° from (001) in a direction 36° from a [110]. Double-axis x-ray topography revealed misfit-dislocation sources in the as-grown samples with an average density of about 60 cm−2, although the distribution of these sites was not homogeneous. The progression of dislocation nucleation and growth was observed during subsequent rapid thermal annealing (800°C, 20s-320s). Physical heterogeneities were identified as dislocation sources, and they gave rise to orthogonal misfit dislocation bundles, which on a macroscopic scale resemble crosses. Upon longer annealing, a more homogeneous distribution of defects was observed without measurable relaxation. These original defects did propagate; however, they did not spur a cross-slip multiplication sequence.

The preparation of buried epitaxial layers of a compound ABx in a matrix of the material A can be performed by allotaxy [1]. In the first process step a distribution of ABx precipitates is prepared in the matrix A by codeposition of A and B. This contribution reports on the spatial distribution and the crystallographic orientation of NiSi2precipitates in the Si- matrix. Cross-section transmission electron microscopy was utilized to characterize the samples. The observed depth distribution of Ni in the Si matrix differs remarkably from the calculated distribution given by the deposition rates of Si and Ni. This redistribution of Ni results in two well distinguishable bands of NiSi2precipitates - a narrow one and a broad one - in the Si matrix. The narrow band consists of epitaxial NiSi2 precipitates; and a mixture of epitaxially and twinned grown NiSi2precipitates is formed in the broad band. Under certain deposition conditions self-ordering of the NiSi2precipitates in the narrow band has been observed parallel and perpendicular to the growth direction. In these cases the diameter of the epitaxial NiSi2precipitates varies between 12 and 50 A and the distance between them is in the order of some 10 Å.

Recent results indicate that compliant substrates offer significant promise as a new approach for strain management in semiconductors. The potential applications include 1) the growth of device-quality highly mismatched materials on dissimilar substrates, and 2) the lateral control of material properties resulting from the effects of strain on bandstructure and/or growth dynamics. A significant amount of research in this area is dedicated to the reduction of extrinsic processing effects resulting from compliant substrate fabrication, and the development of simple models for understanding the observed reduction in defect density and/or strain in the epitaxial films grown on compliant substrates. A recent focus in our work has been on the growth of GaN on a novel and easily removable substrate -lithium gallate- for the regrowth on a bonded GaN template. The first step in this approach is the optimization of the growth of GaN on lithium gallate. In addition, this approach requires the use of an appropriate bonding layer to reduce the strain or defect production during growth due to coefficient of thermal expansion mismatches between the GaN sample and the handle wafer. Our work in this area will be highlighted in the context of an overview of various compliant substrate approaches and current results that indicate their efficacy.

We demonstrate a novel technique, based on low-energy electron microscopy, by which inhomogeneous uniaxial strain at the (001) surface of Si can be mapped quantitatively. Using this technique on silicon-on-insulator wafers, we determine the surface strain field induced by a single 60° dislocation and show that such extended defects can be used as monitors of heteroepitaxy-induced changes in the surface strain.

Because of the large lattice mismatch between InAs and GaAs, the growth of the former on the (001) surface of the latter undergoes a well-known transition from a layer-by-layer mode to an island mode at an equivalent coverage of 1–2 monolayers (ML). We have observed a suppression of this transition when growth proceeds under a simultaneous thallium flux. The thallium is not significantly incorporated into the InAs layer; however, approximately I ML may remain at the interface. The effect of the thallium on the electronic properties of the InAs is investigated.

We have performed calculations of Sn deposition on Cu(111) and Cu(100) surfaces. The atomic interactions are described by modified embedded atom method (MEAM) potentials. This is a modification of the embedded atom method (EAM) to include higher moments in the electron density. We find the at low coverages Sn deposited on Cu(111) leads to the formation of a two-dimensional (2D) alloy phase with a p (√3 × √3)-R 30° structure which is stable up to temperatures of 900K. These results are in agreement with ion-scattering experiments of thin films of Sn on Cu(111). For deposition of Sn on Cu(100), a 0.25 monolayer (ML) coverage results in the formation of a stable 2D alloy phase with a p(2 × 2) structure. This result is also in agreement with LEED measurements.

We report on the first known growth of high-quality epitaxial Si via the hot wire chemical vapor deposition (HWCVD) method. This method yields epitaxial Si at the comparatively low temperatures of 195° to 450°C, and relatively high growth rates of 3 to 20 Å/sec. Layers up to 4500-Å thick have been grown. These epitaxial layers have been characterized by transmission electron microscopy (TEM), indicating large regions of nearly perfect atomic registration. Electron channeling patterns (ECPs) generated on a scanning electron microscope (SEM) have been used to characterize, as well as optimize the growth process. Electron beam induced current (EBIC) characterization has also been performed, indicating defect densities as low as 8×104/cm2. Secondary ion beam mass spectrometry (SIMS) data shows that these layers have reasonable impurity levels within the constraints of our current deposition system. Both n and p-type layers were grown, and p/n diodes have been fabricated.

X-ray diffraction has been used to study the mask-induced strain in GaAs layers grown by the liquid phase epitaxial lateral overgrowth (ELO) on (100) GaAs substrates. SiO2 mask has been investigated to produce seeding areas for the ELO growth. It has been found that SiO2 attracts the ELO layers, which leads to their pronounced bending towards the oxide film and to the appearance of vertical strain in laterally grown parts of ELO. When SiO2 is removed by selective etching this strain disappears. We show evidence that the bending of ELO layers is reduced when the density of substrate dislocations is increased. This is explained as being due to enhancement of the initial vertical growth rate by dislocations supplying steps on the upper surface of ELO.

In this paper we describe observations of novel interactions between clusters of Ag deposited on the clean (001) Cu surface. The experiments are analogous to those performed by Gleiter and co-workers in the 1970's, where grain boundary orientations in particles of Cu and Ag supported on single crystal metal substrates were studied. Upon annealing close to the melting point, these particles (∼10–100μm in diameter) were found to rotate on the surface, forming low-energy grain boundary configurations with the substrate. The particles studied in our experiments are ∼104 times smaller, and show rather different behavior. In the case of Ag nanoparticles we have observed a novel phenomenon, which we call ‘contact epitaxy’, involving the formation of several monolayers of epitaxially oriented Ag at the Cu surface upon contact between this surface and the Ag cluster. The phenomenon may be understood from molecular dynamics simulations of the ‘soft impact’ between the nanoparticle and surface, which indicate that the ordered layers form within picoseconds of contact. We will discuss the mechanisms by which ‘contact epitaxy’ is believed to occur.

The transition temperature Tc for the AlAs growth to change from/to a nucleation mode and step-flow mode have been studied on vicinal GaAs substrates (A-surface and B-surface) in molecular beam epitaxy (MBE) and atomic hydrogen-assisted MBE (H-MBE) using reflection high-energy electron diffraction (RHEED). The lowering of Tc was clearly observed in H-MBE compared to conventional MBE. For growth of AlAs on vicinal GaAs substrate in H-MBE, atomic H is thought to promote not only the re-evaporation of Al adatoms on the terrace, but also the incorporation of Al at the step edges, thereby facilitating a step-flow growth mode at a lower temperature than in MBE. The differences in the fundamental growth mode between on A-surface and B-surface have also been studies based on the differences in the atomic structure between the two substrates.

Doping results from Ar+-laser-assisted chemical beam epitaxy with triethylgallium, tris(dimethylamino) arsenic and silicon tetrabromide as group-HI, group-V and dopant precursors respectively are reported. Enhancements in the n-type doping concentration are observed with laser irradiation in the investigated substrate-temperature range 390°C – 500°C. With a 300 W/cm2 irradiation power density, an increase in the carrier concentration by 70 times is obtained at 390°C substrate temperature. A numerical model developed by us for epitaxial growth and doping with the above precursors is used to assess the contribution of laser-induced thermal heating to the observed doping increase. A reaction scheme for photo-induced decomposition of physisorbed silicon tetrabromide is proposed. A kinetic rate equation for the photolysis is derived and used to estimate the absorption cross section required to reproduce the observed concentration enhancements resulted from laser irradiation. The possibility is established that dramatic increases in carrier concentration at low growth temperatures are due to photolysis of physisorbed silicon tetrabromide.

Epitaxial zinc-blende AIN films as thick as 2000Å were deposited on Si (100) substrates by plasma source molecular beam epitaxy (PSMBE). The metastable zinc-blende form of AIN was observed to occur when pulse d.c. power was supplied to the PSMBE hollow cathode source. Reflection High Energy Electron Diffraction (RHEED) showed that the films possess a four fold symmetry. X-Ray Diffraction (XRD) revealed two strong peaks corresponding to the (200) and (400) reflections from the zinc-blende AIN. The lattice parameter of the films was calculated to be approximately 4.373Å. TEM, performed on one of the films, revealed that the AIN is cubic, single crystalline and epitaxial with respect to the Si (100) substrate.