The recent progress in epitaxial technology is now opening the age of Atomic Position Controlled Epitaxy (APCE) . Toward this technology, the understanding of the elemental growth process is basically important. In this article, the recent understanding on the elemental growth process in GaAs MBE is reviewed and it is pointed out that there are contradicting experimental results in the determination of surface diffusion length of Ga in GaAs MBE, The important problems to be solved to get APCE technology are finally discussed.
Features of electronic states and their wavefunctions in various quantum microstructures are reviewed, including not only well-studied systems such as quantum wells and superlattices, but also newly-emerging systems such as quantum wires and quantum boxes. Novel transport and optical processes in such systems are discussed to clarify their physical origins as well as their impacts on the birth of new devices and also the substantial improvement of existing device performances. Future challenges to enable the formation of quantum wires and boxes with feature sizes of 100Å are summarized.
Atomic layer epitaxy has been developed for III-V compounds using metalorganic and hydride sources. The growth rate was clearly self-limited under a wide range of growth conditions. Epitaxial layers of high purity without carbon contamination could be grown. The growth mechanism was studied and a model based on dissociative adsorption of group III source molecules was proposed. Strained-superlattices (GaAs) m (GaP) n were grown and exhibited an ideal self-limiting mechanism even for the monolayer superlattice case. The selective growth of fine patterns and good uniformity of the epitaxial thickness on a large-scale wafer showed that ALE is promising for a process technology.
Recent advancements in molecular beam epitaxy are reviewed with special emphasis on the control down to a monolayer. Extensive studies have succeeded in shedding light on atomic scale growth mechanisms, which enabled the development of novel growth technologies. Though submicron scale terraces are now realized, much effort is still necessary for meeting the requirements from advanced quantum effect devices.
Fabrication of quantum wire structure is reviewed. Until now, two different approaches are reported. One is using lithography for writing pattern and regrowth for burying. The other is fabrication by single-growth using adequate processed substrate. Principles and important points of these methods are pointed out in this review. Preliminary results of quantum wire laser is also reported as application of quantum wire structure for devices.
New GaAs quantum dot structures, called tetrahedral quantum dots (TQDs) are proposed to make a zero-dimensional electron-hole system. The TQDs are surrounded by crystallographic facets fabricated using selective area MOCVD growth on (111) B GaAs substrates. The calculated energy sublevel structures of 0-dimensional electrons in GaAs TQD show large quantum size effects, because electrons are confined three-dimensionally. GaAs and AlGaAs tetrahedral facet structures on (111) B GaAs substrates partially etched into a triangular shape were grown using MOCVD. Tetrahedral growth with (110) facets occurs in the triangular areas. The cathodoluminescence intensity map for GaAs tetrahedrons buried in AlGaAs shows the tetrahedral dot array.
We have recently made nanometer-scale structure fabrication using field evaporation in the scanning tunneling microscope (STM) for a Si (111) sample with a W tip by changing the polarity, magnitude and duration of the voltage applied to the tip. A theoretical framework that can interpret/predict the experimental results and similar results reported so far is discussed.
Concept of atomic layer etching is described. Experimental results on the atomic layer con-trolled etching are reported. Under alternative supply of Cl2, the etching rate saturates at 1/3 mono-layer/cycle as a function of Cl gas feeding rate. By using Cl radical, the etching rate saturates at one atomic layer/cycle as a function of Cl gas feeding rate under a proper etching condition.
The mechanism and the method of atomic layer growth of copper-based oxide superconducting thin films are discussed. Taking advantage of the two dimensional layered structure of high-Tc superconductors, these layered structures have been constructed by a layer-by-layer deposition method using laser MBE method. The basic structural parameters based on the CuO2 sheets have been successfully changed to control the high-Tc superconductivity with these methods.
The principal role of silicon-fluorine bonds in the chemical nature of HF-etched Si surfaces has been studied by angle resolved X-ray photoelectron spectroscopy. The fluorine coverage and the native oxide growth thickness have been systematically measured as functions of HF concentration, pure water rinse time, air or N2+O2 gas exposure time and gas phase H2O concentration. It is found that the existence of Si-F bonds of about 0.12 monolayers on the surface strongly suppresses the native oxide growth. This is explained by a model in which Si-F bonds chemically stabilize the surface reactive sites such as atomic steps as supported by the result of the layer-by-layer oxidation of Si.
A summary is given of the outline of the preparation technique of Langmuir-Blodgett (LB) films as a tool to construct man-made molecular assemblies which are of potential use in molecular electronics. The conductive Langmuir-Blodgett films are briefly reviewed as representing the recent endeavors of developing novel functional materials in the form of ultrathin films. The analytical model of flow orientation is touched upon as an example of the quantitative approach to the dynamic aspects of the LB preparation technique.