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We proposed heavily doped silicon between insulators (HDSBI) MOSFETs to improve electrical characteristics of local BOX MOSFETs by using simple structures that combine local BOX regions with additional doped regions. HDSBI MOSFETs have heavily doped regions between local BOX regions, in which acceptors or traps are introduced. Simulated electrical characteristics demonstrated that they can suppress the SCEs and the kink effect, as well as the self-heating effect (SHE), which is suppressed by conventional local BOX MOSFETs. We elucidated how the additional doped regions in HDSBI MOSFETs suppress the SCEs and the kink effect. We concluded that HDSBI MOSFETs are suitable for applications, such as multi-purpose system-on-chip on which both short-channel logic circuits and high drive current circuits are integrated.

Silicon-on-insulator (SOI) MOSFETs have advantages over conventional bulk MOSFETs in terms of their electrical characteristics, but also have inherent disadvantages due to the presence of their buried-oxide (BOX) layers. In this paper, focus was placed on drain electric flux passing via the BOX layer to the body region as an influence that induces disadvantages such as drain-induced barrier lowering in SOI MOSFETs. The electric flux in the BOX layer was visualized using stream functions, and was quantitatively evaluated for the first time ever. The results showed the dependence of electric flux on relative permittivity and the BOX layer thickness. These outcomes confirmed that the subthreshold slope (SS) in short-channel SOI MOSFETs is affected strongly by electric flux detouring via the BOX layer, and the compact model of the enhancement of SSs due to the flux is proposed.

In this paper, the authors propose novel metal-oxide-semiconductor field-effect transistor (MOSFET) types featuring additional L-shaped counterdoped areas in the source and/or drain regions of silicon-on-insulator (SOI) MOSFETs to reduce drain-induced barrier lowering (DIBL) through the buried oxide (BOX) layer. The L-shaped region in the drain area shields the BOX layer from penetration by the drain electric field, thereby reducing DIBL in the body region. Simulation of the electrical characteristics of these novel MOSFETs demonstrated more remarkable DIBL suppression and subthreshold slope performance in short-channel regions than in conventional SOI MOSFETs. In addition to this suppression, these novel MOSFETs suppress breakdown voltage more effectively than conventional SOI MOSFETs. The authors concluded that the proposed devices are capable of contributing to the scaling of SOI MOSFETs in ultralarge-scale integration circuits.

Due to an oversight in the above paper (ibid., vol. 60, no. 1, pp. 260-267, Jan. 2013), Figs. 4-9 appeared in black and white in print. They should have printed in color, as shown here.

We characterized the distribution of trap states in silicon-on-insulator (SOI) layers in epitaxial layer transfer (ELTRAN) wafers and in low-dose separation by implanted oxygen (SIMOX) wafers. We measured the front- and back-gate characteristics of MOSFETs with SOI layers of different thicknesses. We used the current-Terman method to estimate the trap states at the gate oxide (GOX)/SOI interface and at the SOI/buried oxide (BOX) interface separately. As a result, we concluded that the high-density trap states in the SOI layers in SIMOX wafers cause a gate-voltage shift, which is attributed to the charged trap states only in the inversion layer. We also found that the trap states are distributed within about 30 nm from the SOI/BOX interface in the SOI layer in SIMOX wafers, which indicates that the distribution of trap states originates from the oxygen implantation that is peculiar to the SIMOX process.

Two-dimensional device simulation was performed on silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect-transistors (MOSFETs) with various gate length L g various top Si layer thickness t Si and various buried oxide (BOX) layer thickness t BOX . As a result, it was found that when t BOX is large, short channel effect (SCE) cannot be suppressed in a fully depleted (FD) MOSFET only by the simple scaling rule maintaining the ratio of L g to top Si layer t Si more than four. It was also found that the scaling rule breaks down more seriously in a fully inverted (FI) MOSFET. It was confirmed that electric field from the drain region penetrates easily into thick BOX layer, which causes drain-induced barrier lowering (DIBL) at the top Si/BOX interface in deep sub-micron gates SOI MOSFETs. Consequently, it was concluded that the DIBL can be suppressed efficiently by reducing t BOX even in a FI MOSFET.

We demonstrated a new application of body current to quantitative characterization of carrier lifetime in thin silicon-on-insulator (SOI) films. Previously, we have characterized the energy distribution of trap density in fully depleted (FD) SOI metal oxide semiconductor field effect transistors (MOSFETs), and furthermore, we have demonstrated that recombination at SOI/buried oxide (BOX) interface can suppress kink effect. However, little is known about electronic properties of thin SOI layers. Hence, in this study, we proposed a new electric measurement technique for characterizing recombination lifetime in thin SOI layers from body currents of MOSFETs. We investigated the dependence of inverse hole lifetime 1/τ h on substrate bias V sub . Furthermore, we considered that the converged value gives the lifetime of bulk recombination, τ bulk , while the variation of 1/τ h gives the lifetime of surface recombination, τ surface . We also succeeded in reproducing the tendency of 1/τ h -V sub curves by numerical 3D device simulation. Our approach could separate the effect of bulk recombination and that of surface recombination on SOI layers.

A quantum mechanical (QM) approach for modeling and simulation of MOS devices, covering the whole operation region, was proposed. This formulation is applicable continuously from the subthreshold to the saturation regions, since it exactly treats the QM effects on the in-depth distribution of the gate induced carriers in the channel by solving one dimensional Poisson equation and Schrodinger equation self-consistently and it treats the lateral drift–diffusion transport using quasi-Fermi potential. A QM simulator was implemented using this QM approach. This QM simulator was verified by classical three-dimensional device simulator, CADDETH, in the whole range of operation of bulk MOSFET with low dopant density where QM effect is negligible. The QM simulation elucidated that the threshold voltage shift in thin SOI MOSFETs in saturation region as well as in linear region results from energy shift of the lowest conduction electron level and effective increase of gate oxide thickness.

We succeeded in reproducing experimental phenomena characteristic of metal-oxide-semiconductor field-effect-transistors (MOSFETs) fabricated on separation by implanted oxygen (SIMOX) wafers by device simulation. Previously, we have found that SIMOX wafers have energetically localized traps at silicon-on-insulator (SOI)/buried oxide (BOX) interface, and we have also found that the traps cause current drops, suppression of kink and dependence of carrier lifetime on substrate bias in SIMOX MOSFETs. We developed a three-dimensional device simulator considering energetically localized traps at SOI/BOX interface, and we clarified that the novel phenomena in SIMOX MOSFETs come from the traps. We applied this simulator to three-dimensional MOSFET structures, and we estimated surface recombination velocity at SOI/BOX interface on SIMOX wafers.

We characterized trap states at silicon-on-insulator (SOI)/buried oxide (BOX) interfaces in epitaxial layer transfer (ELTRAN) wafers and in low-dose separation by implanted oxygen (SIMOX) wafers. We formulated a simple analytical form to obtain the distribution of density of trap states from a comparison of the experimental transconductance and simulated transconductance of SOI metal oxide semiconductor field effect transistors (MOSFETs). We observed dips in back gate transconductance in MOSFETs on low-dose SIMOX wafers. Consequently, we concluded that "acceptor-like electron traps" with the density of 5 ×1012 cm-2eV-1 near the conduction band edge Ec and "donor-like hole traps" with the density of 1012 cm-2eV-1 near the valence band edge Ev are distributed in the forbidden band of Si at SOI/BOX interfaces in low-dose SIMOX wafers, while the trap density at SOI/BOX interfaces is less than 1011 cm-2eV-1 in ELTRAN wafers. We also found that the kink effect is suppressed in MOSFETs on low-dose SIMOX wafers with a high density of trap states at the SOI/BOX interface.

Electron wave interference effects in GaAs/AlGaAs coupled quantum dots have been studied at 30 mK in magnetic fields with different coupling strength between two dots. In a strong coupling regime, the existence of global trajectories which span two dots was suggested, while in a weak coupling regime, the trajectories were found to be limited in each single dot.

The authors examined the origins of high-density trap states in silicon-on-insulator (SOI) layers by means of scanning probe microscopy measurements, I-V characteristics in MOSFETs, and micro-Raman measurements in SOI wafers, including bonded wafers and separation by implanted oxygen (SIMOX) wafers having different root-mean-square values of roughness at the SOI/buried oxide (BOX) interface. As a result, it was concluded that nanoscale roughness at the SOI/BOX interface causes local mechanical stress a few tens of nanometers from the interface and that this stress induces the SIMOX-specific high-density trap states for holes as well as for electrons in the SOI layers.

Fractal behavior in X-ray diffraction (XRD) from a Ga(As, P) fractal-structured lattice grown by atomic layer epitaxy (ALE) has been discussed. Fibonacci progression for the 11th generation was used as the fractal arrangement of lattice. Self-similar geometry particular to fractal has been confirmed by a conventional XRD measurement system using CuK α1 radiation. In addition, the XRD spectrum shows a good agreement with the result of fast-Fourier transform (FFT) analysis, and the perfect fractal behavior for the 11th generated lattice arrangement. We can conclude that ALE is the most powerful tool for synthesis of the fractal-structured lattice.

Atomic layer intermixing at pseudomorphic interfaces has been evaluated directly by changing of electronic states due to disordering in (GaAs) m (GaP) 1 ( m =2, 3, 4) superlattice grown by atomic layer epitaxy (ALE). The results show the critical change of the electronic structures due to atomic layer intermixing at GaAs/GaP hetero interface. The interdiffusion coefficients are about two orders of magnitude higher than values of the self-diffusion. It is suggested that microscopic and inhomogeneous strain effects are closely related to the exchange of neighboring atoms at the interface.

In recent studies of disordered quantum dot arrays, it was found that a re-entrant metal–insulator transition occurs in these structures as the gate voltage is varied, even though there is no change in carrier density or disorder. Here, we study resonances that appear with the quantum Hall effect in these dot arrays. Several resonances are observed on the side of the plateaus, which may be due either to charging of isolated islands or to transmission resonances in the quantum point contacts. Heating of the carriers causes these peaks to decrease with an energy relaxation time comparable to that of the dots themselves.

Fractal behaviour in the magneto-conductance fluctuations of mesoscopic systems has been predicted using semiclassical theory and observed experimentally in semiconductor billiards. Surface-gate billiards provide an ideal environment for investigations of fractal behaviour due to the ease with which parameters in the experimental system can be tuned. In this study we vary temperature and billiard size to investigate the classical and quantum limits of the semiclassical theory for fractal magneto-conductance fluctuations.

We present evidence for a re-entrant metal–insulator transition that arises in quantum dot arrays as the gate voltage is used to sweep their density of states past the Fermi level. The form of the temperature variation of the conductance observed in these arrays can be accounted for using a functional form derived from studies of the metal–insulator transition in two dimensions, although the values obtained for the fit parameters suggest that the behavior we observe here may be quite distinct to that found in two dimensions.

Laser ablation is a successful process to fabricate Er-doped nanocrystalline Si (nc-Si) thin films with high doping densities. The formed samples show intense 1.54 μm emission at room temperature. The high doping density of Er and the widening effect of the bandgap of the host nc-Si caused by fabricating Si in the nanometer scale give rise to a remarkable increase of the emission intensity of Er at room temperature. The time-response measurements under direct and indirect excitations reveal that the Er 3+ ions doped in nc-Si are dominantly excited by an energy transfer process from the photo-generated electron–hole pairs. This gives hope to realizing the Si-based optical devices by current injection.

Subband formation in fractal-structured lattice (FSL) has been investigated by photo-reflectance (PR) measurements. Ga(As,P) FSL was grown on a (001) GaAs substrate by atomic layer epitaxy (ALE). Fibonacci progression for the 11th generation was used as the fractal arrangement of lattice. The X-ray diffraction shows no periodicity but long-range order. The PR spectra show formation of the singular subband originating from the fractal lattice arrangement, and are consistent with a transfer matrix calculation on the FSL. These results suggest that the FSL arrangement can cause interference of electron wave function in the FSL.

Temperature dependence of photoluminescence (PL) spectra of an electrostatically prepared modulation-doped quantum dot array is investigated. We report a strong temperature dependence of the enhanced PL near the Fermi energy between 0.4 and 4.2 K under a negative bias condition, where an interconnected quantum dot array is formed. This strong temperature dependence suggests that the Fermi-surface-mediated many-body interaction between a photo-created hole and the electron-gas plays an important role in the observed enhanced PL near the Fermi energy.

To fabricate a two-dimensional array structure which has potential application to a nano-devices array, we formed imbricate step/terrace structures on precisely-controlled vicinal Si substrates. From STM observation, it was found that on Si(1 0 0) surfaces offsetting towards 〈0 1 0〉 direction by 4°, a rectangular-imbricate structure, where only a 2×1 structure is formed and dimers on neighboring terraces are at right angles to each other, was obtained after annealing of the Si wafers in ultra-high vacuum. Furthermore, formation of a larger-scale rectangular imbricate step/terrace structure, using anisotropic etching of Si substrate, was observed by AFM. This is expected to be a novel technique for fabricating ultra small capacitance arrays on Si wafers for nano-scale array circuits.

We report on a bias voltage-dependent photoluminescence (PL) peak near the Fermi level in n-type modulation-doped quantum dot arrays. A remarkably sharp peak with a spectral width of less than 0.1 meV is observed near the Fermi level in PL at 0.4 K, which shows strong temperature dependence. This peak is considered to be due to the Coulomb interaction between the electron gas and a photo-generated hole.

We discuss the observation of an unusual type of localization in split-gate quantum dots and quantum-dot arrays. While no evidence for its existence is found prior to biasing the gates, the localization persists to conductance values as high as $50{e}^{2}/h$ and is not destroyed by the application of a weak magnetic field. The carrier density in the dots remains constant over the range of gate bias studied and these characteristics suggest that the localization is quite distinct to that studied previously in two-dimensional semiconductors. We suggest that a confinement-induced enhancement of the electron-electron interaction may be responsible for the localization and propose a simple functional form which allows us to account for its variation as a function of either temperature or source-drain voltage.

The nonlinear conductivity of an array of quantum dots, formed by split-gates on a GaAs/AlGaAs heterostructure, is studied. Previously, this array was shown to exhibit a gate bias-induced localization behavior at low temperatures, similar to the insulating state found in 2D systems. Here, we study the effect of source–drain bias potential on the heating of the electron system in the dots. We find that the scaling of conductance with this bias voltage can be described by an equation similar to that for temperature. In addition, we determine the effective temperature and energy-relaxation time. This relaxation time appears to decay as T−3/2 at higher temperatures, but shows a saturation at low temperatures.

The dynamics of resonantly excited 1s-HH excitons in GaAs single quantum wells is studied by picosecond transient reflection and photon echo. At low exciton densities and 5 K superradiant decay takes place of free excitons and a coherence length is found of ∼0.2 μm. At higher exciton densities transport is observed induced by exciton–exciton collisions.

The quantum-size effect is investigated theoretically in model nanocrystalline/amorphous mixed-phase Si structures. We show that the peak energies of the imaginary part of the dielectric function of the model structures shift as a function of the size of nanocrystalline Si and the thickness of amorphous Si which surrounds the nanocrystalline Si. This effect cannot be explained by the conventional quantum confinement model because of the lack of an apparent potential which confines electrons within the nanocrystalline Si embedded in amorphous Si. Atomic positions of the amorphous Si are modeled by a Monte Carlo calculation with the Stillinger-Weber potential for the interaction between Si atoms. The electronic calculation is based on an empirical pseudopotential method with basis states represented in a real-space grid. Dielectric functions of modeled structures containing up to 13 824 Si atoms are calculated, which has been made possible by calculating a time-dependent representation of the linear-response function.

We present investigations of the fractal behaviour of magneto-conductance fluctuations in semiconductor billiards as a function of temperature. The introduction of finite phase coherence by nonzero temperatures is found not to suppress fractal behaviour in the experimental data. Instead, we show that the fractal dimension decreases with increasing temperature and we present a remarkable similarity between the phase coherence time and the fractal dimension.

Landau-level formations are studied theoretically for highly optically populated InP strained self-organized quantum dots for magnetic fields below 45 T. A self-consistent Hartree calculation is performed in real space with the higher-order finite difference method. A transition of the discrete states due to a potential confinement at 0 T to Landau-level-like structures for high magnetic fields is demonstrated.

The fabrication of (GaAs) m (GaP) n low dimensional short-period superlattices (LD–SPSL) by using advanced atomic layer epitaxy (ALE) techniques is demonstrated. (GaAs) m (GaP) n SPSL were grown on V-grooved GaAs substrates by using the ALE growth mode switching technique, between anisotropic (for GaAs growth) and isotropic (for GaP growth) ALE. The lateral confined systems composed of well-defined (GaAs) m (GaP) n SPSL have been confirmed via transmission electron microscopy (TEM). The zone-folding effect has been observed in the (GaAs) m (GaP) n LD–SPSL via photoluminescence (PL) measurements. Also multi-quantum wire structures (MQWR) composed by (GaAs) m (GaAs 0.8 P 0.2 ) n SPSL, which were strong-coupled ( m =20, n =5) and weak-coupled ( m =20, n =20) systems, were fabricated. The coupling and the lateral confinement effects have been clearly observed via PL and PL excitation measurements.

An O ( N ) algorithm is proposed for calculating the density of states and the linear response functions of noninteracting electrons. This algorithm is simple and suitable to parallel- and vector-computation. Since it avoids O ( N 3 ) computational effort of matrix diagonalization, it requires only O ( N ) computational efforts where N is the dimension of the statevector. The use of this O ( N ) algorithm is very effective since otherwise we have to calculate a large number of eigenstates, i.e. the occupied one-electron states up to the Fermi energy and the unoccupied states with higher energy. The advantage of this method compared to the Chebyshev polynomial method recently developed by Wang [27, 28] is that our method can calculate linear response functions without any storage of huge statevectors on external storage.

The low temperature magneto-resistance of quasi-ballistic, corrugated quantum wires has been studied. In the region near zero magnetic field, the magneto-resistance exhibits a series of clear oscillations which simulations reveal to be associated with multiple backscattering of electrons from the intentionally induced gate corrugation. This backscattering, in turn, gives rise to a strong scarring of the probability density in the wire, the details of which are easily related to classical scattering trajectories within it.

Studies of the phase breaking time in open quantum dots reveal a value of the order of a few tens of picoseconds at low resistances, which increases by as much as one order of magnitude as the quantum point contact leads are narrowed to support just a few modes. In addition, the value of the phase breaking time in the high resistance regime shows considerable device dependent variations, indicative of a sensitivity of phase coherence to device dependent disorder. In order to account for these observations, we suggest an interpretation of phase breaking which invokes the discrete nature of the level spectrum in the open dots and which emphasizes the role of the quantum point contacts in selectively exciting dot eigenstates.

Quantum dot arrays have been prepared by applying a bias voltage on a metal mesh structure on a n-type modulation-doped quantum well. A pronounced enhancement of the photoluminescence spectra near the Fermi level has been observed at the bias voltage of −0.5 V.

We report geometry-induced fractal behaviour analogous to fractional Brownian motion in the low-field magneto-conductance fluctuations of a mesoscopic semiconductor billiard. Such fractal behaviour was recently predicted to be due to the trajectory trapping behaviour of the mixed (regular/chaotic) phase space generated by the soft-walled nature of the billiard potential profile. Hence, our results constitute a possible experimental observation of the infinite hierarchical nature of this mixed phase space. Preliminary investigations into the effects of temperature and gate bias, which directly control electron coherence and billiard potential profile, are presented.

We study theoretically and experimentally a nominally stadium shaped quantum billiard, a device in which the classical dynamics is expected to be chaotic. Using self-consistent solutions for the confining potential in our calculations, we find, in agreement with experiment, that the magnetotransport is dominated by a periodic oscillations, characteristic of regular orbits in the structure, indicating the stability of non-chaotic classical trajectories.

InGaAs/GaAs quantum wire (QWR) and dots were fabricated on GaAs (111)A vicinal substrates by the atomic layer epitaxy (ALE) technique. In0.25Ga0.75As QWR structures were formed on metal–organic vapor phase epitaxy grown homogeneous multiatomic height steps on GaAs (111)A vicinal substrates misoriented toward the [112] direction. In photoluminescence measurement only one spectrum, which shows strong polarization dependence, was observed. The result and its narrow full width at half maximum of 10 meV imply that the elimination of the wetting layer and excellent size uniformity are realized by the ALE technique. Spontaneous alignment of InGaAs quantum dots was also achieved by the ALE method. Boxlike shaped dot arrays of which height is restricted by the step height indicate that the ALE growth on the (111)A vicinal surface has an effect on not only the arrangement but also on the size and shape control of quantum nanostructures.

We report geometry-induced fractal behaviour in the low-field magneto-conductance fluctuations of a mesoscopic semiconductor billiard. Such fractal behaviour was recently predicted to be induced by the mixed (chaotic/regular) phase space generated by the soft-walled billiard potential, and our results constitute a possible experimental observation of the infinite hierarchical nature of this mixed phase space. Preliminary investigations of the effects of temperature and gate bias, which directly control the electron coherence and billiard potential profile, are presented.

We report a pseudopotential calculation of a model nanocrystalline Si embedded in amorphous Si up to 13 824 atoms and show a novel quantum size effect in this model system. This large scale pseudopotential calculation has been made possible by a real-time real-space higher-order finite difference method. It is shown that the peaks at around −1 and −2 eV shift to higher energy with decrease in size of nanocrystalline phase.

Si nanocrystallites formed in amorphous Si (a-Si) show intense blue luminescence at room temperature. The samples are fabricated by crystallization of a-Si thin films, which leads to a large size dispersion of the nanocrystallites due to a random distribution of strain fields in the a-Si phase. In this work, we demonstrate a process of controlling the crystallite size by doping Er in the a-Si layers. The doped Er atom introduces additional strain in the a-Si matrix and behaves as a nucleation center during the crystallization. It is demonstrated that the average size of the Si nanocrystallites is almost independent of the crystallization time for a certain Er concentration and a certain annealing temperature. By controlling the Er density and crystallization temperature, we have fabricated a series of nanocrystalline (nc) Si samples having the average sizes from 3 to 10 nm. The smallest size achieved here is 2.7 nm. A bright blue luminescence from the Si nanocrystallites as well as a 1.54 μm emission from the doped Er3+ ions were observed up to room temperature.

Periodic structures with high uniformity have been fabricated by metal-organic vapor-phase epitaxy on GaAs (1 1 1)A vicinal surfaces. Scanning electron microscope and atomic force microscope surface images show strict dependence on substrate off-direction, growth temperature (Tg), and V/III ratio. Giant steps with long-range continuity and high uniformity have been formed on GaAs (1 1 1)A substrates misoriented towards the [112¯] direction. In addition, the heights of the giant steps show the saturation at high Tg and the value is independent of substrate off-angle. On the other hand, homogeneous zigzag steps have emerged on the substrate off toward the [0 0 1] azimuth after the growth at high Tg, whereas relatively rough steps were formed on both substrates at low Tg. The results indicate the growth-mode transition from step-flow to facet formation as growth temperature gets higher.

In this review we describe the results of magneto-transport studies in open quantum dots, in which electronic motion is expected to be predominantly ballistic in nature. The devices themselves are realized in different semiconductor materials, using quite distinct fabrication techniques. Electron interference is an important process in determining the electrical properties of the devices at low temperatures and is manifested through the observation of periodic magneto-conductance fluctuations. These are found to result from selective excitation of discrete cavity eigenstates by incoming electrons, which are directed into a collimated beam by the input point contact. Under conditions of such restricted injection, quantum mechanical simulations reveal highly characteristic wavefunction scarring, associated with the remnants of a few classical orbits. The scarring is built up by interference between electrons, confined within the cavities over very long time scales, suggesting the underlying orbits are highly stable in nature. This characteristic is also confirmed by the results of experiment, which reveal the discrete components dominating the interference to be insensitive to changes in lead opening or temperature. The fluctuations decay with increasing temperature, although they can nonetheless still be resolved at a few degrees kelvin. This characteristic is confirmed by independent studies of devices, fabricated using very different techniques, further demonstrating the universal nature of the behavior we discuss here. These results therefore demonstrate that the correct description of electron interference in open quantum cavities, is one in which only a few discrete orbits are excited by the collimating action of the input lead, giving rise to striking wavefunction scarring with measurable magneto-transport results.

We investigate precise departures fromh / eperiodicity in Aharonov–Bohm oscillations observed in the low temperature magneto-resistance of quantum dots. Period-doubling is apparent over well defined ranges of magnetic field, outside of which the oscillations revert to their single period. The precise nature of the doubling is reflected in a Fourier analysis of the oscillations, and is also confirmed by the results of self-consistent calculations. While the origin of this effect remains unclear we discuss several possible mechanisms, and also briefly consider the conditions necessary for observation of frequency-doubled oscillations.

Er was doped into porous Si and nanocrystalline Si thin films. Sharp and intense photoluminescence at 1.54 μm was observed up to room temperature. We demonstrate that Er 3+ ions are excited by an energy transfer process from the excited electron-hole pairs in the host materials and no direct excitation of Er 3+ ions can be observed. This fact suggests that the Er emission could be used as a probe to determine absorption edges of the hosts. This idea was first applied to Er-doped porous Si. Identical excitation edges of the 1.54 μm emission and the visible emission from porous Si have been demonstrated. We suggest that the method should also be valid for measuring the absorption edge of a nanometer-sized Si host material even if it is not luminescent.

Giant steps with high uniformity and continuity have been successfully formed by metalorganic vapor-phase epitaxy on GaAs (1 1 1)A vicinal surfaces for the application of quantum wire fabrication. The step height is more than 30 monoatomic layer at a growth temperature of 660°C. The surface morphologies obtained from scanning electron microscopy and atomic force microscopy measurements show the straight steps on (1 1 1)A substrates misoriented toward [2 1 1] direction with high uniformity. Terrace uniformity and step continuity are improved as the off-angle increases. A straight section of a step exceeding 10 μm was obtained on 4° off-substrate. Fluctuation has also been suppressed within 1 monoatomic layer height on this vicinal substrate.

A quantum wire array has been fabricated on GaAs (111)A vicinal substrates by continuous growth of metalorganic vapor phase epitaxy (MOVPE) and atomic layer epitaxy (ALE). The formation of multi-atomic height steps with high uniformity and continuity has been achieved by MOVPE on GaAs (111)A vicinal substrates misoriented toward [211] direction. In the ALE process, the growth rate of the GaAs layer on the (111)A terrace has been controlled with the source gas feeding sequence and the growth temperature. Growth suppression on the (111)A terrace and selective adsorption of source molecules at the step region has been confirmed. A GaAs/GaAs 0.9 P 0.1 quantum wire structure has been fabricated on the (111)A vicinal surface using an ALE selective growth technique.