Dynamical Reflection High-energy Electron Diffraction Research Articles

An isolating algorithm for automated surface structure determination using RHEED

An isolating algorithm is investigated for automated surface structure determination using reflection high energy electron diffraction (RHEED). This algorithm combines standard numerical minimization procedures with dynamical RHEED calculations, and treats different physical fitting parameters discriminatingly for different diffraction conditions. The procedure is illustrated using an ideal example of Ge(001)2 × 1 surface. It is shown that to a large extent the problem of non-uniqueness of the physical quantities obtained from the numerical procedure is largely avoided.

Dynamical calculations for RHEED from MBE growing surfaces. III. Heteroepitaxial growth and interface formation

The birth-death growth model previously used in parts I and II for simulating molecular beam epitaxy growth of a single type of atom species has been generalized to describe the growth of heterostructures involving the deposition and diffusion of multiple atomic species. Detailed dynamical reflection high-energy electron diffraction (RHEED) calculations have been made to investigate various aspects of RHEED intensity oscillations, including the measurement of growth rate and alloy composition, interface and recovery effects, control of quantum well widths, as well as changes of the character of RHEED intensity oscillations.

Dynamical RHEED calculations of relaxation on Au(110)–2×1 reconstruction

Dynamical calculations of reflection high-energy electron diffraction (RHEED) from the 2 × 1 missing row reconstruction of the Au(110) surface have been simulated as a function of surface-atom relaxation at different incident glancing angles using the multislice approach with the edge-patching method. The results demonstrate that the diffracted-beam intensity is extremely sensitive to the surface structure; small surface relaxations lead to large amplitude changes, which is consistent with similar claims by previous authors using different methods. The high surface sensitivity of RHEED indicates that it can be used to fingerprint surface relaxations if a reliable simulation tool is available.

Dynamical RHEED from MBE growing surfaces

A practical computing procedure has been developed for calculating reflection high energy electron diffraction (RHEED) from molecular beam epitaxy (MBE) growing surfaces. A birth-death model is employed to describe the epitaxy growth on the surfaces, and the diffracion is treated dynamically. A typical calculation of RHEED intensity from a GaAs(001) MBE growing system consisting of a bulk substrate crystal and up to ten growing surface layers takes five seconds on a VAX 8800 system.

Dynamical Calculations of RHEED Intensity Evolution During MBE Growth

Reflection high energy electron diffraction (RHEED) has become well established as one of the most powerful and versatile techniques for growth and surface studies of semiconductor films prepared by molecular beam epitaxy (MBE). In particular the technique of RHEED intensity oscillations has been used routinely to calibrate beam fluxes and alloys composition and to control the thicknesses of quantum wells and superlattice layers.Although several interpretations have been proposed for the strong oscillations in RHEED intensity during MBE growth, full dynamical calculations have been done only for an artificial surface consisting of a periodic array of surface steps. The enormous amount of computation involved prevents the dynamical theory being applied to a more realistic epitaxically growing system. In this paper we report a simple and practical method for calculating dynamical RHEED from MBE growing surfaces.We first consider epitaxial growth on a low-index surface. The growth is simulated by using a perfect layer growth model and a diffusive growth model.

Frequency-domain analysis of time-dependent reflection high-energy electron diffraction intensity data

A technique has been developed for computerized acquisition and frequency-domain analysis of dynamic reflection high-energy electron diffraction (RHEED) intensity data obtained during growth by molecular-beam epitaxy (MBE). This technique allows the rapid, accurate determination of the frequency of RHEED oscillations, not only when these oscillations are well resolved, but also when the growth conditions yield oscillations that are too poorly resolved to permit frequency analysis by conventional procedures. The new technique has been used to study transients in the growth of AlGaAs on GaAs substrates and also to investigate the heteroepitaxial growth of GaAs on Si.

Surface step structure of a lens-shaped Si(001) vicinal substrate

A dynamic reflection high-energy electron diffraction (RHEED) intensity analysis was used to characterize the growth kinetics of Si(001) vicinal surfaces. The doubling of monolayer steps into a bilayer step during growth and the breakup of a bilayer step into monolayer steps after growth was investigated for the surface tilted toward the [110] azimuth. Bilayer-mode RHEED intensity oscillations up to 1000 °C were found during the growth for the surface tilted toward the [120] azimuth. The anisotropy of surface diffusion with respect to the direction of dimerization bond and the asymmetric step properties was strongly related to the complicated growth mechanism of Si(001) vicinal surfaces.

Rheed Observation of Lattice Relaxation During Ge/Si(O01) Heteroepitaxy

ABSTRACTWe report the dynamic RHEED (reflection high energy electron diffraction) observation during Ge/Si(001) heteroepitaxy at various growth temperatures. The RHEED intensityanalysis and the in-plane lattice constant analysis reveal a growth fashion and lattice relaxation. Both of them depend strongly on growth temperature.

Reflection high resolution analytical electron microscopy: a technique for studying crystal surfaces.

Reflection electron microscopy (REM), reflection high energy electron diffraction (RHEED), reflection electron energy-loss spectroscopy (REELS), and energy dispersion x-ray spectroscopy (EDX) have been comprehensively used as a technique, termed reflection high resolution analytical electron microscopy (RHRAEM), for studying the structures of the bulk crystal GaAs (110) surfaces by transmission electron microscopy (TEM). The simultaneous observations of surface topography imaging, the surface diffraction mechanism with RHEED, surface atomic inner-shell excitations with REELS, and surface chemical compositions with EDX provide a systematic description of the atomic structure and chemical structure of the surface. The surface channelling effect has been observed in GaAs (110) with REELS, which may provide a basis for localizing surface foreign atoms with ALCHEMI. The theoretically predicted surface-resonance wave has been observed directly in the RHEED pattern; the surface-captured Bragg reflection wave have been identified. It is shown that surface chemical compositions can be determined by analyzing the EDX spectra obtained in the REM case. Finally, the surface monolayer resonance characteristic of the RHRAEM has been confirmed by calculations with dynamical RHEED theory.

Comparative study of the growth processes of GaAs, AlGaAs, InGaAs, and InAlAs lattice matched and nonlattice matched semiconductors using high-energy electron diffraction

We have examined the effect of growth temperature and growth interruption time on molecular-beam-epitaxial growth of GaAs, Al0.3Ga0.7As, and InxGa1−xAs on GaAs substrates and In0.53Ga0.47As and In0.52Al0.48As on InP substrates using dynamical reflection high-energy electron diffraction as an in situ probe. We have studied the time taken for a rough growth front to recover in the absence of growth as a function of growth temperature for these compounds. It is found that while GaAs and InGaAs surfaces can recover in 15–20 s under ideal growth conditions, Al0.3Ga0.7As surfaces take ≊45 s, and In0.52Al0.48As surfaces take several minutes to recover. Our results also suggest that smoothening of the growth front occurs by rearrangement of the surface atoms, rather than by re-evaporation. We have also studied the effect of strain induced by mismatch on growth modes in the case of InxGa1−xAs on GaAs. Our studies suggest that the presence of strain inhibits the surface migration of adatoms during growth and thus tends to generate a rougher growth front.