This paper reviews the present status of self processes for semiconductor nanostructures. The term “self-process” includes the concepts of self-assembly and self-organization, which is clearly distinguished following Lehn's definition. We describe self-assembled InAs islands grown on a GaAs(100) surface and self-organized InGaAs disks grown on a GaAs(311)B surface. We touch on the future aspects of a novel role for nanostructures via semiconductor selfprocesses.
We report nanostructure formation by controlling self-organization on Ga-adsorbed and ultra-thin oxide covered Si surfaces. On the Ga-adsorbed surface, we have formed clean Si stripe areas with atomically accurate size by Ga desorption from the step edges. Selective adsorption of Sb on such surfaces makes it possible to form nanoscale lateral p-n junction structures where Ga-adsorbed (p-type) and Sb-adsorbed (n-type) areas exist alternately on the surfaces. On the ultra-thin Si oxide film (<1 nm thickness) surface, we have found the phenomenon that 10 nm-size clean Si areas appear in the focused electron beam (EB)-irradiated areas after heating. After growing and heating Ge film on such surfaces, we have formed 10 nm-size Ge islands at given areas as a result of the selective surface reactions.
Wafer-scale control of nanofabrication on Si using selforganization processes are described. Unit cells of surface reconstruction, atomic steps, and domain boundaries of the reconstruction can be used as templates to control arrangement of self-organized nanostructures. We demonstrate that atomic-step network can be organized by controlling the step motion during surface atom evaporation, employing etched patterns formed by lithographic technique. Step/domainboundary network can be modified by using step-flow growth. Ge quantum dot network is self-formed on the surface with well organized templates. Strain distribution on the substrate surface is important for the size and shape control of Ge quantum dots. Chemical reaction control plays an important role in fabricating semiconductor-insulator-conductor nanostructures. In Si/Ge nanostructure, reaction selectivities between Si and Ge can be utilized to form oxide and silicide layers at the Si/Ge interfaces.
(GaP)n (InP)m short period superlattices (SLs) are grown on GaAs(N11), (011) and (100) substrates by gas source molecular beam epitaxy. Transmission electron microscopy and scanning tunneling spectroscopy observations show that the SLs grown on GaAs(N11)A (N=2-5) have lateral-composition-modulated dot/columnar structures with a lateral period of about 10-25 nm, while on GaAs(100) and (011), wire/vertical-superlattice structures are formed. On the other hand, the SLs on GaAs(111) show no lateral composition modulation and have quasi-perfect lateral superlattice structures. Photoluminescence (PL) peak energies are greatly dependent on substrate orientation and monolayer numbers n, m corresponding to the lateral composition modulation. Optical properties of GaP/InP SL/InGaP multilayer quantum dots (MQDs) are investigated and light emitting diodes (LEDs) are fabricated.
In this paper, we show the effect of atomic hydrogen (H) irradiation on the fabrication of InGaAs quantum dots (QDs) by self-organization process in molecular beam epitaxy. The size of QDs decreased by atomic H irradiation. The high density InGaAs QDs are formed uniformly by atomic H irradiation, while they are distributed mainly along the step edges without H irradiation. On the other hand, atomic H irradiation also improved photoluminescence (PL) properties. PL intensity increase and line width decrease were observed with atomic H irradiated samples. In addition, we fabricated InGaAs QDs on GaAs(311)B substrate. The ordered structures of QDs were obtained on this surface, and the effects of atomic H irradiation were also observed in growth.
Recently, several works have been reported concerning the adsorption of atomic hydrogen (H) on metal (e. g. Ag)-induced Si(111)√3×√3 surface phases, in which the displacive adsorption of H causes the formation of metal clusters with nanometer size. These phenomena have disclosed an interesting process of self-organization from 2 D metal layer into 3 D clusters induced by adsorption of H. However, as for the interaction of H with other surface reconstructions besides √3×√3, only a few studies have been reported. Since the H-induced structural rearrangement of metal/Si surface phases is thought to be dependent on their original surface structures, it is possible for an appropriate surface phase to be self-organized into peculiar structures in a different manner than the above-mentioned 2 D-3 D transformation using the interaction of H. In this paper, we will show interesting behaviors of metal atoms and substrate Si atoms against H adsorption on metal/Si surfaces besides √3×√3, using the Si(100)2×1-Sb and the In/Si(111) surface phases as examples.
We have studied surface electronic properties of GaAs covered by self-organized InAs dot structures through tunneling spectroscopic measurements. Differential conductance properties on n-type (001) GaAs samples covered with an InAs wetting layer or InAs dot structures were measured by a scanning tunneling microscope operated in air under laser light. The modulation effects on the tunneling properties by the laser irradiation reveals that the surface electronic properties, such as band bending and surface Fermi level, of the n-GaAs sample with the InAs wetting layer are very similar to those of a bare n-GaAs sample. In contrast, additional deposition of InAs over the wetting layer, which forms InAs dots, leads to a drastic change in the electronic properties near surface.
The influence of Ar+ion energy in XPS sputter depth profiling of amorphous oxide film/substrate interface has been examined. It was found that the oxide film of metal substrate was formed at the interface mainly due to the knocked-on oxygen atoms during the sputter depth profiling. Furthermore, the low energy sputtering has been recognized to successfully reduce the changes in chemical state at the interface in addition to the improvement of depth resolution. The precise depth profiling with low energy sputtering was applied to the analysis of the O-ion implantation into substrate during deposition of oxide films by do magnetron sputtering methods. It was found that the population of O-ion implantation was larger in the reactive sputtering method compared to the oxide target sputtering method. Difference properties between the both sputter deposition methods such as a crystalline growth can be explained in terms of the O-ion implantation effect during the deposition.
Photomechanical response of the polymer monolayers having an azobenzene (Az) side chain was successfully visualized by Brewster angle microscopy (BAM) and atomic force microscopy (AFM). In situ BAM observation that covers the sub-millimeter scale range revealed clear photoinduced morphological and rheological changes. By following the photoinduced morphological changes of an isolated single domain, a couple of hitherto unknown properties have been unveiled, for example, non-linearity involved in the film expansion process, intrinsic magnitude of film expansion at zero pressure, dependence on light intensity and so forth. By AFM that observes the ranges of micrometer to nanometer levels, it was found that even on a mica surface, the Az containing monolayer shows a reversible photoinduced film deformation under highly humid conditions. These visualization techniques provided a great deal of complementary unique information which covers the scale ranges between the macroscopic Langmuir trough experiments and scale spectroscopic observations at a molecular level.
BB-dan is Japanese brand name of ball bullets for toy guns. The bullets are plastic spheres with a diameter of 6mm, and are very cheap, for example 4, 000 bullets costs you about 1, 000 yen (equivalent to approximately 8 US dollars). Ball crystal models called some times “marble ball models” are constructed by using these tiny ball bullets. Here I give the name BB-dan model, because the bullet is called BB-dan. The constructing methods are detailed. The pictures of models for a hexagonal compact structure, a body centered cubic structure, a zinc-blende type structure and a Si(111) 7×7 reconstructed structure are given.