The growth of InAs quantum dots on GaAs(001) shows a new aspect of non-classical nucleation, namely the dynamic formation of preferred growth sites within the substrate. Using fully in situ scanning tunnelling microscopy - molecular beam epitaxy, we observe rapidly changing transitions between domains of different surface reconstruction a few nm in size. Nucleation of 3D islands is preferred on one particular reconstruction, blurring the line between heterogeneous and homogeneous nucleation as traditionally understood on a static substrate.
Electronic transition is shown to be important to elemental dynamics of epitaxy, as well as the kinetic mass transport by heat. Thermal desorption flux of In adatom at the InAs surface is consistently explained on the basis of phonon-stimulated electronic transition of the adatom charge state by electron tunneling. This strongly suggests that the thermal desorption is essentially electronic in nature. The effectiveness of the low-temperature scanning tunneling microscope (LT-STM) characterization in combination with the molecular beam epitaxy (MBE) system of III-V semiconductors is discussed. This instrument allows us to clarify fundamental microscopic dynamics during crystal growth induced by electronic processes with enhanced visibility of quantum mechanics of electrons and atoms. The equivalence of electrons and phonons as excitation sources in the case of the electronic transition is verified. Due to this equivalency, it is shown that the LT-STM equipped with the MBE system is a promising complement to in situ observation during MBE.
Novel processes on the GaAs(001) surfaces during molecular beam epitaxial growth are investigated using ab initio-based approach incorporating growth conditions such as temperature and beam-equivalent pressure. Using this approach with Monte Carlo simulations, behaviors of cation and anion atoms on the GaAs(001) surfaces are exemplified by InAs wetting layer formation and N-incorporation. Hetero-epitaxial growth of InAs wetting layer does not proceed due to simple successive In adsorption but change of its atomic arrangements to reduce the strain to form surface In-As dimer and missing dimer region on the surfaces. N-incorporation processes are also dominated by decrease of the strain forming energetically favorable Ga-N bonds in the third layer via series of events such as adsorption of N-As dimer, substitution of N for As located in the third layer, and As dimer deosorption to form N-pair in the third layer.
An experimental approach to crystal growth dynamics using synchrotron X-ray diffraction is discussed. In the study of crystal growth, analysis of imperfect crystals lacking three-dimensional periodicity is inevitably required. Every real crystal has surfaces, at which the periodicity in the surface normal direction is lost. Defects generated in epitaxial films result in the diffuse scattering around the Bragg peaks. Quantum structures having a finite size yield extended diffraction that gives information about the size, shape and internal strains of the crystal. Although such diffuse scattering is much weaker than the bulk Bragg diffraction, recent development of the synchrotron light source has enabled the in situ measurement of it during crystal growth. In this article, studies on surface structures, evolution of defects in growing films and the growth of nanostructures under molecular-beam epitaxy conditions are presented as well as a brief overview of the instrumentation.
Dislocation-mediated strain relaxation during lattice-mismatched InGaAs/GaAs(001) heteroepitaxy was studied through in situ x-ray reciprocal space mapping (in situ RSM). At the synchrotron facility SPring-8, a hybrid system of molecular beam epitaxy and x-ray diffractometry with a two-dimensional detector enabled us to perform in situ RSM at highspeed and high-resolution. Using this experimental setup, the strain relaxation processes were classified into four thickness ranges with different dislocation behavior. In order to discuss this observation quantitatively, a strain relaxation model was proposed based on the Dodson-Tsao's kinetic model, and its validity was demonstrated by good agreement with the experimental residual strain. In addition to the single InGaAs layer, strain relaxation processes in multi-layer structures are discussed.
High performance group III nitride semiconductor based light-emitting diodes and laser diodes most fabricated by metalorganic vapor phase epitaxy (MOVPE). In situ monitoring in MOVPE is the key process in device manufacturing. These information can be feedback to growth condition and find its mechanism. In this paper, we reported the analyzation of MOVPE growth in GaInN single layer and GaInN/GaN superlattice on GaN by in situ XRD monitoring.
Low-energy electron microscopy (LEEM) is a powerful tool for investigating surface dynamical processes such as crystal growth and phase transition. After reviewing the image formation principle of LEEM along with its distinctive characteristics, we present three examples of in-situ LEEM observations of crystal growth; growth of C_<60> monolayers on Si(111), growth of twinned epitaxial Si layers on Si(111), and growth of graphene on metals by carbon segregation.
It is known that lateral growth of semiconductors is important to bend and annihilate threading dislocations during epitaxial growth. In order to understand the initial growth process of AlN during solid source solution growth, we developed in-situ observation system for high-temperature liquid/solid interfaces. In this study, we used transparent substrate, i.e., AlN/sapphire template, so as to observe high-temperature liquid/solid interfaces through the substrate from the bottom. Though a polycrystal formed because of melt-back etching during the initial stage of growth; nevertheless, initial growth process was successfully observed by the in-situ observation system. This in-situ observation system could be a powerful tool for investigating interfacial phenomena at high-temperature liquid/solid interfaces and optimizing crystal growth conditions.