As a consequence of strain relaxation, Ge coherent islands on Si(001) substrates evolve to different shapes as islands grow. By measuring the size and the strain simultaneously in a large population of individual islands using two simple and robust plan-view transmission electron microscopy-based techniques, we can identify island shapes easily because island shape is a function of strain. We briefly introduce the mechanisms of these two techniques. We then show that there is a metastable shape of Ge islands involved in the shape transition between pyramids and domes. The strain relaxation changes discontinuously as islands grow from pyramids to the metastable form and then finally to domes indicating that the shape transition between pyramids and domes is first order. We also show that the shape of this metastable island is a truncated dome and the faceted planes are {103}.

InAs/GaAs superlattices with thin (0.5–1 monolayer) δ-InAs insertions were grown by molecular beam epitaxy at low (150–200°C) temperature. The as-grown samples contained up to 1020 cm−3 arsenic antisite defects. Transmission electron microscopic study revealed no extended defect and showed that the real thickness of δ-InAs insertions is 3–4 monolayers. This thickness seems to be due to short-range roughness of the growth surface. Low diffuse scattering and extended interference picture were observed for such superlattices by x-ray diffraction study. Superlattices of two-dimensional cluster sheets were produced by annealing of the δ-InAs/GaAs superlattices at 500–600°C. Precipitation of excess arsenic at InAs δ-layers was found to be accompanied by enhanced In-Ga intermixing, roughening the InAs δ-layers, and smoothing the x-ray interference picture. No evidence for any self-ordering in the system of nanoscale As clusters was revealed using x-ray mapping in reciprocal space.

Effect of pulsed magnetic field induced self-organized generation of 3-D spatially regular structures of oxygen-vacancy contained clusters of nanometer scale has been observed in silicon crystals grown by Czochralski method (Cz-Si). The effect has been studied by means of ultra-soft X-ray spectroscopy, scanning tunneling microscopy and potential probe measurements. Mechanisms responsible for the effect have been discussed.

We use a scanning tunneling microscope (STM) capable of imaging the growing layer at high temperature during molecular beam epitaxy (MBE) to study the epitaxial growth of Germanium on Silicon and the decay of Ge islands. The periodicity of the (2×N) reconstruction of two-dimensional Ge layers on Si(001) is measured as function of the Ge coverage. Strain energy drives the formation of the (2×N) reconstruction and Si/Ge intermixing. A comparison to total energy calculations predicting the periodicity of the (2×N) reconstruction is used to estimate the amount of Si-Ge intermixing near the surface. The evolution of the size and shape of individual “hut clusters” is measured and explained by kinetically self-limiting growth. The relaxation of kinetically a determined morphology towards equilibrium is followed for a Ge layer on Si(111). Strained two-dimensional as well as partially relaxed three-dimensional islands dissolve and are soaked up by larger three-dimensional islands which are dislocated and therefore fully relaxed.

We present real-time measurements of stress relaxation kinetics during epitaxial growth obtained using a wafer-curvature-based technique optimized for in situ studies. Depending on the temperature and misfit strain, different mechanisms of stress relaxation are observed. In heterolayers of InGaAs grown on GaAs (001) substrates, relaxation occurs by a dislocationmediated mechanism. In SiGe layers grown on Si (001) substrates at elevated temperature, relaxation occurs by the formation of islands on the surface. These islands elastically relax misfit stress without the introduction of dislocations at the island-substrate interface.

X-ray scattering and transmission electron microscopy (TEM) have been used to study short-range order in Al1−xlnxAs thin films grown by molecular beam epitaxy. Two samples grown on (001) InP at temperatures of 370°C and 400°C are characterized. The first exhibits simultaneous triple-period-A and CuPt-A short-range order with a rather short correlation range of about 2.4 nm normal to the (111) planes. Within these (individual) planes the concentration, however, is uniform over a considerably greater distance – about 6 to 9 nm – leading to a highly anisotropic scattering. This observation of triple-period short-range ordering in a sample that exhibits 2×1 surface reconstruction during growth is unexpected. We also report on the first observation of the coexistence of triple-period-A and CuPt-B short-range order. The diffuse scattering exhibits significant intensity anomalies that we attribute to atomic displacements associated with the short-range order. The second sample exhibits CuPt-B short-range ordering with scattering that is significantly streaked, suggestive of lamellar-shaped ordered domains. This sample also exhibits intensity anomalies that must be associated with atomic displacements. The first sample contains a high density of twin lamellae, while both samples contain high densities of stacking faults leading to additional narrow streaking along symmetry-allowed 〈111〉 directions. These growth faults most likely arise from the relatively low growth temperatures.

We report the first observation of atomic long range ordering in the metal-oxide based wide bandgap (3.68 eV) ZnMgO alloy semiconductor thin films grown on sapphire (0001) by pulsed laser deposition. The ZnMgO system has the hexagonal wurtzite structure. The atomic ordering was deduced from the observations of forbidden x-ray diffraction peaks in the wurtzite structure. We show that under optimum thin film growth conditions, Zn and Mg preferentially occupy hcp sublattice. The relative intensity of the superlattice peak was largest for the Mg content in the range of 10%, which is about 50% of the solubility of Mg in ZnO. The observation of long range order in ZnMgO alloy semiconductor is quite important in the context of understanding issues related to the growth kinetics, surface reconstruction, and phase stability of metal-oxide based heterostructures and devices.

Migration-Enhanced Epitaxy (MEE) has been successfully employed to grow epitaxial films of the ternary compound CuInSe2 on (001) GaAs that are ordered in a CuAu crystallographic structure rather than the compound's equilibrium chalcopyrite structure. Evidence for this structural polytype is provided by XRD, TEM–TED, and Raman scattering data. Film growth under the conditions employed for this study occurs in a Stranski-Krastanov mode. The effects of growth system parameters and overall stoichiometry on 3–D island formation are described, including our observation that ordering of those islands into quasiperiodic self-assembled arrays occurs only in the case of nonstoichiometric copper excess.

CuPt ordering in III/V semiconductor alloys is significant because of the dependence of bandgap energy on degree of order. This paper presents the effects of surfactants isoelectronic with P on ordering in GaInP grown by organometallic vapor phase epitaxy. Each of the three surfactants studied, As, Sb, and Bi, is found to result in disordering for layers grown using conditions that would otherwise produce highly ordered materials. The amount of surfactant required in the vapor phase (as the organometallic precursors TMAs, TESb, and TMBi) increases as the volatility of the group V element increases. Thus, the amount of TEAs required to produce disordered GaInP is approximately two orders of magnitude greater than for TMBi.

For Sb, the disordering is shown to be caused by a replacement of [110 ] P dimers on the nominally (001) surface by Sb dimers with the same orientation. For Bi, a marked change in the step structure coincides with the loss of order. For singular (001) substrates, island formation is suppressed by Bi.

The low-temperature (5K) photoluminescence (PL) of partially-ordered GaInP2 is spatially resolved using high-resolution (from ˜ 0.2μm-0.7μm) scanning optical microscopy, revealing the spatial variation in band gap energy and the spatial origin of the ordering-induced low-energy emission and the associated ‘quantum-dot-like’ narrow spikes which appear when examining areas smaller, or of comparable size, than a single ordered domain. The large number of spectra taken within a micronsized area allow a detailed look at the statistical variation in band-gap energy and lineshape. A systematic study of a series of samples where the order parameter varies from η ˜ 0 to 0.45 shows that for the most highly-ordered samples, the statisitical distribution of excitonic energy and linewidth show evidence of exciton localization, which is also clearly seen by examining the spatial maps of the excitornic energy and linewidth extracted from the measured spectra.

The mechanism causing the CuPtB-type ordering of InGaP grown lattice matched to GaAs was investigated by in-situ reflectance anisotropy spectroscopy (RAS/RDS). Experiments were performed during InGaP growth in metal-organic vapour phase epitaxy (MOVPE). From the experiments it can be concluded that bulk ordering only occurs when InGaP growth is performed under phosphorus-rich (2×1)-like surface conditions. Bulk ordering completely disappears under growth conditions which cause a less-phosphorus-rich (2×4)-like surface dimer configuration.

We present a comprehensive overview of the large spectroscopic evidence on the influence of ordering on the Raman and infrared spectra of partially ordered GaInP2. Our phonon mode calculation within the adiabatic bond charge model describes the appearance of new phonons and also the optical anisotropy.

In the last ten years, the scanning transmission electron microscope (STEM) has become capable of forming electron probes of atomic dimensions making possible a new approach to high-resolution electron microscopy, Z-contrast imaging. Formed by mapping the intensity of high-angle scattered electrons as the probe is scanned across the specimen, the Z-contrast image represents a direct map of the specimen scattering power at atomic resolution. It is an incoherent image, and can be directly interpreted in terms of atomic columns. High angle scattering comes predominantly from the atomic nuclei, so the scattering cross section depends on atomic number (Z) squared. Z-contrast microscopy can therefore be used to study compositional ordering and segregation at the atomic scale. Here we present three examples of ordering: first, ferroelectric materials, second, III-V semiconductor alloys, and finally, cooperative segregation at a semiconductor grain boundary, where a combination of Z-contrast imaging with first principles theory provides a complete atomic-scale view of the sites and configurations of the segregant atoms.

We examine CuPt-B atomic sublattice ordering in Ga0.51In0.49P (GaInP) and Ga0.47In0.53As (GaInAs) III-V alloy films grown by atmospheric- and low-pressure metalorganic chemical vapor deposition on singular and vicinal (001) substrates. The influences of growth conditions and substrate miscut on double- and single-variant ordered microstructures are investigated using transmission electron microscopy (TEM). Relatively thick (>1–2 litm) double-variant ordered GalnP and GaInAs films show complementary superdomain formation. Single-variant ordered films on <111>B-miscut substrates contain single-phase domains, separated by antiphase boundaries (APBs). The appearance of APBs in TEM dark-field images is anticipated from electron diffraction theory.

Nominally lattice-matched GaInAs layers grown by metal organic vapor phase epitaxy on InP substrates have been studied using high-resolution x-ray diffraction (HRXRD) to determine the growth conditions under which ordering is introduced. HRXRD provides an independent means to quantify the order parameter of semiconductor heterostructures as well as the ordering on different {111} planes, i.e., double variant ordering. This independent means to determine ordering provides for a better understanding of the effects of ordering on the electronic and optical properties. Double variant ordering was observed for epitaxial layers grown on exact (001) InP substrates, with an order parameter of about 0.1 in both variants. For substrates that were miscut by 6 degrees, single variant ordering was detected. In these cases, an order parameter as high as 0.66 was measured for certain growth conditions. The layers grown on vicinal substrates are all of high crystalline quality, those on (001) substrates exhibit some mosaic spread.

We demonstrate the formation, and the electronic and optical properties of a novel type of semiconductor superlattice in spontaneously ordered GaInP alloys. The most frequently observed ordered structure in MOCVD grown GaInP has CuPt symmetry where the ordering directions occur in the two [111]B directions, corresponding to two distinct ordered variants. A new type of superlattice, termed an orientational superlattice, emerges as the ordered domains are stacked in a sequence whereby the ordering direction switches alternatively from the [111] direction in one domain to the [111] direction in the next domain. The novelty of this type of superlattice lies in that there is neither a band-gap nor an effective mass discontinuity along the superlattice axis. When the GaInP epilayer is grown on an exact (001) or [111]A tilt GaAs substrate, the two ordered variants are equally favorable. Thus, ordered domain twins appear in ordered GaInP epilayers. We present a comparitive study between the single-variant ordered structure and the double-variant ordered superlattice structure, using TEM and time-resolved differential absorption. We show that for a same order parameter, the band-gap of an orientational superlattice is higher than that of a single-variant ordered structure, and the in-plane optical anisotropy between the [110] and [110]B directions is greatly enhanced due to the superlattice effect. The experimental results are explained in terms of the band structure of the orientational superlattice.

We show the results of joined studies of the free electron concentration and x-ray diffuse scattering from heavily doped GaAs:Te single crystal as a function of controlled annealings at high temperatures 700–1200°C and Te concentration 1018− 2 1019 cm−3 from the range, where the free electron concentration saturates. Changes of electron concentration caused by annealings are accompanied by structural changes, both being in a high coincidence and reversible versus annealing temperature On a basis of the microscopic model of x-ray diffuse scattering from a solid solution, newly proposed here, we argue that impurity atom pairs arise, locally in a crystal, when the free electron concentration is lowered by annealing. We suppose that the electron localization is caused by impurity atom pairs, supporting recently published results.

The triple-period (TP)-A and CuPt-A type ordering, which have been so far reported only for MBE grown alloys, were observed, in addition to CuPt-B type ordering, in Al0.5In0.5As alloys grown by MOVPE at 500°C. This indicates that (2×3) and (1×2) surface reconstructions occur on the surface even during MOVPE growth, although the (2×1) surface reconstruction and CuPt-B type ordering are dominant for the growth conditions examined.

The luminescence properties of a single lnAs self-assembled quantum dot (QD) are studied by confocal scanning optical microscopy at low temperature. The observation of single QDs has been accomplished by epitaxial growth of QDs samples with low QD density (less than one QD per μm2) required by the diffraction limited spatial resolution of the microscope. In thick QDs with large confinement energies biexciton binding energies of up to 5.0 meV are found, while in thin and more weakly confined QDs the electron wavefunction penetrates into the surrounding barriers causing reduced biexciton binding energies of less than 2.0 meV. This result can be understood in terms of theoretical calculations of biexcitonic complexes in QDs with finite potential barriers.

We apply the technique of x-ray diffraction to the determination of the crystallographic structure and the quantitative measurement of the order parameter of ZnSnP2 epitaxial layers. In bulk, ZnSnP2 it is possible to obtain highly ordered distribution of Zn and Sn atoms in the cation sublattice, but epitaxial growth often produces partially ordered layers. The ordered and disordered phases correspond to the chalcopyrite and sphalerite structures and their respective band gaps are 1.66 and 1.24 eV. Since ZnSnP2 is almost lattice-matched to GaAs. it is interesting candidate for optoelectronic applications.

Samples used in this work were grown by gas source molecular beam epitaxy on GaAs substrates. Slight variations in growth conditions could be induced to produce partially ordered and disordered structures. Chalcopyrite ordering is determined by the observation of several characteristic reflections identifying the lower symmetry of this structure. For example, reflections from (101), (217) and (611) planes, strictly forbidden for sphalerite, were measured. The quantitative determination of the order parameter could be made by comparing intensities of a carefully chosen set of measured and calculated reflections. We show that while kinematic approximation can be used to model weak superstructure reflections, in the calculation of the strong, low-angle, fundamental reflections used for intensity normalization it is necessary to take into account extinction effects. Order parameters varying from 0 to 30% were obtained.