Device characteristics of In0.5Ga0.5As/GaAs quantum dot infrared detector (QDIP) have been enhanced with hydrogen plasma treatment. After the hydrogen (H) plasma treatment, the dark currents were noticeably decreased and photoluminescence (PL) intensity was increased by H-passivation of interfacial traps between quantum dots and GaAs and of non-radiative defect centers caused during QD growths. Photo response, which could not be observed in as-grown QDIP due to large dark currents which obscured the photocurrent signal, was measured successfully after H-treatment due to H-passivation.

Si-based photonic materials and devices, including SiGe/Si quantum structures, SOI and InGaAs bonded on Si, PL of Si nanocrystals, SOI photonic crystal filter, Si based RCE (Resonant Cavity Enhanced) photodiodes, SOI TO (thermai-optical) switch matrix were investigated in Institute of Semiconductors, Chinese Academy of Sciences. The main results in recent years are presented in the paper. The mechanism of PL from Si NCs embedded in SiO2 matrix was studied, a greater contribution of the interface state recombination (PL peak in 850~900 nm) is associated with larger Si NCs and higher interface state density. Ge dots with density of order of 1011 cm-2 were obtained by UHV/CVD growth and 193 nm excimer laser annealing. SOI photonic crystal filter with resonant wavelength of 1598 nm and Q factor of 1140 was designed and made. Si based hybrid InGaAs RCE PD with η of 34.4% and FWHM of 27 nm were achieved by MOCVD growth and bonding technology between InGaAs epitaxial and Si wafers. A 1616 SOI optical switch matrix were designed and made. A new current driving circuit was used to improve the response speed of a 44 SOI rearrangeable nonblocking TO switch matrix, rising and falling time is 970 and 750 ns, respectively.

A comparison among the possible nonlinear photonic interactions for scalable nanometer networks and quantum gates as well as for coherence retention in solids is made theoretically, and then numerical plottings are given, on the basis of the dipole length estimated from our µ-PL (microphotoluminescence) spectra of GaAs/AlGaAs coupled quantum dots (QDs) having a pair of 0.3 meV splittings. Furthermore, prospective device concepts based on these nonlinear multipolar interactions are given.

This paper outlines the method of constructing single-electron logic circuits based on the binary decision diagram (BDD), a graphical representation of digital functions. The circuit consists of many unit devices, BDD devices, cascaded to build the tree of a BDD graph. Each BDD device corresponds to a node of the BDD graph and operates as a two-way switch for the transport of a single electron. Any combinatorial logic can be implemented using BDD circuits. Several subsystems for a single-electron processor have been constructed using semiconductor nano-process technology.

We observed the optically forbidden energy transfer between cubic CuCl quantum dots coupled via an optical near-field interaction using time-resolved near-field photoluminescence (PL) spectroscopy. The energy transfer time and exciton lifetime were estimated from the rise and decay times of the PL pump-probe signal, respectively. We found that the exciton lifetime increased as the energy transfer time fell. This result strongly supports the notion that near-field interaction between QD makes the anti-parallel dipole coupling. Namely, a quantum-dots pair coupled by an optical near field has a long exciton lifetime which indicates the anti-parallel coupling of QDs forming a weakly radiative quadrupole state.

We make a theoretical study about the laser-induced radiation force exerted on nano materials under a quantum mechanical resonance condition of electronic systems [1] confined in them. In our recent study, we have clarified that the remarkable effects of the electronic resonance appear in the radiation force on the small object whose size is much smaller than the light wavelength; (A) the acceleration on the object gets larger as the size decreases, (B) the peaks with less heat appear in the force spectra even under the resonance condition, (C) the peak position sensitively varies with the nanoscale-size changes. These are useful for the optical manipulation to precisely control the mechanical motions of nano materials. In this paper, toward the experiment to verify the above results, we discuss the dependence of the mechanical motion of nano objects on the width of the incident laser light, and on the diffusion and friction effects assuming that they are floating in the superfluid helium-4 with the cryogenic condition where the electronic resonance effects become conspicuous. The results of calculations show that the particular nano objects, whose resonance energy corresponds to the center frequency of incident laser, can move away from others over macroscopic distance beyond diffusion length. This means that we can observe the distribution of sizes and qualities of nano objects as a macroscopic spatial distribution of them if we prepare appropriate conditions of incident light. We call this new technique 'Nano Optical Chromatography (NOC).'

We have fabricated Al-gate MOS capacitors with a Si quantum-dots (Si-QDs) floating gate, the number of dots was changed in the range of 1.6-4.81011 cm-2 in areal density with repeating the formation of Si dots and their surface oxidation a couple of times. The capacitance-voltage (C-V) characteristics of Si-QDs floating gate MOS capacitors on p-Si(100) confirm that, with increasing number of dots density, the flat-band voltage shift due to electron charging in Si-QDs is increased and the accumulation capacitance is decreased. Also, in the negative bias region beyond the flat-band condition, the voltage shift in the C-V curves due to the emission of valence electrons from intrinsic Si-QDs was observed with no hysterisis presumably because holes generated in Si-QDs can smoothly recombine with electrons tunneling through the 2.8 nm-thick bottom SiO2. In addition, we have demonstrated the charge retention characteristic improves in the Si-QDs stacked structure.

Quantum dots are one of the possible building blocks for the quantum computing device. We discuss on use of carbon nanotubes for fabrication of the quantum dot, in terms of their unique physical properties and energy scales which might be advantageous for functionalities of the quantum computing device. Simple schemes of a charge qubit and a spin qubit are described, followed by the current status of the fabrication and transport measurements of the nanotube quantum dot. Based on the basic properties and the estimated energy scales of the dot, we discuss advantages and problems of the carbon nanotube for the quantum computing device. The nanotube quantum dot may have a great advantage for the spin qubit.

We describe the characteristics of all-optical switching schemes based on semiconductor optical amplifiers (SOAs), with particular emphasis on the role of the fast carrier dynamics. The SOA response to a single short pulse as well as to a data-modulated pulse train is investigated and the properties of schemes relying on cross-gain as well as cross-phase modulation are discussed. The possible benefits of using SOAs with quantum dot active regions are theoretically analyzed. The bandfilling characteristics and the presence of fast capture processes may allow to reach bitrates in excess of 100 Gb/s even for simple cross-gain modulation schemes.

We have demonstrated low-threshold two-dimensional photonic crystal lasers with self-assembled InAs/GaAs quantum dots. Coupled cavity designs of whispering gallery modes are defined in square lattice photonic crystal slabs. Our lasers showed a small 120 µW input pumping power threshold. Actual absorption power is evaluated to be less than 20 µW. Our lasers show high spontaneous emission coupling (β) factors0.1. The mode volumes are expected to be 0.7-1.2 times cubed wavelength by our modelling. Based on threshold analysis, 80 QDs are the effective number of QDs defined as the number of QDs needed to make PC cavities transparent if they are on maximum optical field points. Using the same analysis we found that single quantum dot lasing is likely to occur both by proper alignment of the single quantum dot relative to geometries of photonic crystals and by using sharp QD emission lines in high-Q localized modes.

We discuss photonic crystals (PhCs) with advanced micro/nano-structres which are semiconductor quantum dots (QDs) and micro electro-mechanical systems (MEMS) for the purpose of realizing novel classes of PhC devices in future photonic network system. After brief introduction on advantages to implement QDs and MEMS with PhCs, we discuss optical characterization of PhC microcavity containing self-assembled InAs QDs. Modification of emission spectrum of a QD ensemble due to the resonant cavity modes is demonstrated. We also point out the feasibility of low-threshold PhC lasers with QD active media in numerical analysis. A very low threshold current of 10 µA is numerically obtained for lasing action in the multi dimensional distributed feedback mode by using realistic material parameters. Then, the basic concept for MEMS-controlled PhC slab devices is described. We show numerical results that demonstrate some of interesting functions such as the intensity modulation and the tuning of resonant frequency of cavity mode. Finally, a preliminary experiment of MEMS-based switching operation in a PhC line-defect waveguide is demonstrated.

Optical properties and growth of self-assembled quantum dots (SAQDs) for optoelectronic device applications are discussed. After briefly reviewing the history of research on QD lasers, we discuss growth of InAs SAQDs including the light emission at the wavelength of 1.52-µm with a narrow linewidth (22 meV) and the area-controlled growth which demonstrates formation of SAQDs in selected local areas on a growth plane using a SiO2 mask with MOCVD growth. Then properties of the InGaAs AQDs are investigated by the near-field photoluminescence excitation spectroscopy which reveals gradually increasing continuum absorption connected with the two-dimensional-like (2D-like) wetting layer, resulting in faster relaxation of electrons due to a crossover between 0D and 2D character in the density of states. In the coherent excitation spectroscopy, the decoherence time is determined to be about 15 ps, which is well explained by the phonon induced relaxation mechanism in the SAQDs. Finally, nitride-based SAQDs and perspective of QD optical devices are also discussed.

We analyze electron transport of silicon single-electron transistors (Si SETs) with an ultra-small quantum dot using a master-equation model taking into account the discreteness of quantum levels and the finiteness of scattering rates. In the simulated SET characteristics, aperiodic Coulomb blockade oscillations, fine structures and negative differential conductances due to the quantum mechanical effects are superimposed on the usual Coulomb blockade diagram. These features are consistent with the previously measured results. Large peak-to-valley current ratio of negative differential conductances at room temperature is predicted for Si SETs with an ultra-small dot whose size is smaller than 3 nm.

Our recent progress in GaN-based nanostructures for quantum dot (QD) lasers and vertical microcavity surface emitting lasers (VCSELs) is discussed. We have grown InGaN self-assembled QDs on a GaN epitaxial layer, using atmospheric-pressure metalorganic chemical vapor deposition. The average diameter of the QDs was as small as 8.4 nm and strong photoluminescence emission from the QDs was observed at room temperature. Furthermore, we found that InGaN QDs could be formed even after 10 QD layers were stacked, thus increasing the total QD density. Using these growth results, we fabricated a laser structure with InGaN QDs embedded in the active layer. A clear threshold was observed in the dependence of the emission intensity on the excitation energy at room temperature under optical excitation. We succeeded in demonstrating in lasing action in vertical cavity surface emitting lasers at room temperature with a cavity finesse of over 200.

A novel analog-computation system using quantum-dot spin glass is proposed. Analog computation is a processing method that solves a mathematical problem by applying an analogy of a physical system to the problem. A 2D array of quantum dots is constructed by mixing two-dot (antiferromagnetic interaction) and three-dot (ferromagnetic interaction) systems. The simulation results show that the array shows spin-glass-like behavior. We then mapped two combinatorial optimization problems onto the quantum-dot spin glasses, and found their optimal solutions. The results demonstrate that quantum-dot spin glass can perform analog computation and solve a complex mathematical problem.

The current-voltage characteristics of a single electron transistor (SET) in the resonant transport mode are investigated. In the future when SET devices are applied to integrated electronics, the quantum effect will seriously modify their characteristics in ultra-small geometry. The current will be dominated by the resonant transport through narrow energy levels in the dot. The simple case of a two-level system is analyzed and the transport mechanism is clarified. The transport property at low temperatures (higher than the Kondo temperature) in the low tunneling rate limit is discussed, and a current map where current values are classified in the gate bias-drain bias plane is provided. It was shown that the dynamic aspect of electron flow seriously influences the current value.

We propose a novel opto-electronic memory device using a single quantum dot (QD) and a logic device using coupled QDs (CQD) which performs (N)AND and (N)OR operations simultaneously. In both devices, occupation/unoccupation by a single electron in a QD is viewed as a bit 1/0 and data input/output (I/O) is performed by irradiation/absorption of photons. The (N)AND/(N)OR operations are performed by the relaxation of the electronic system to the Fock ground state which depends on the number of electrons in the CQD. When the device is constructed of semiconductor nanostructures, the main relaxation process is LA-phonon emission from an electron. Theoretical analysis of the device shows that (i) the error probability in the final state converges with the probability with which the system takes excited states at thermal equilibrium, i. e. , depends only on the dissipation energy and becomes smaller as the dissipation energy becomes larger, and (ii) the speed of operation depends on both the dissipation energy and dissipative interactions and becomes slower as the dissipation energy becomes larger if LA-phonon emission is taken into account. If the QDs are InAs cubes with sides of 10 nm and they are separated by the AlSb barrier with a width of 10 nm, the speed of operation and the error probability are estimated to be about 1 ns and about 0. 2 at 77 K, respectively. The basic idea of the device is applicable to two-dimensional (2D) pattern processing if the devices are arranged in a 2D array.

The dipole-dipole interaction among excitons is shown to give rise to an intrinsic nonlinearity, which yields a localized mode in a forbidden band, providing a coherent state for quantum computation. Employing this mode, a quantum XOR (exclusive OR) gate is proposed. A block structure of quantum dot arrays is also proposed, to implement quantum circuits comprising the quantum XOR gates for computation.

We discuss fabrication of InGaAs quantum dot structures using the self-assembling growth technique with the Stranski-Krastanow growth mode in MOCVD, including optical ploperties of the nano-structures. The formation process of the quantum dot islands was clarified by observing the samples grown under various conditions with an atomic force microscope. A trial for self-alignment of the quantum dots was also investigated. On the basis of these results, as the first step toward the ultimate semiconductor lasers in which both electrons and photons are fully quantized, a vertical microcavity InGaAs/GaAs quantum dot laser was demonstrated. Finally a perspective of the quantum dot lasers is discussed, including the bottleneck issues and the impact of the quantum dot structures for reducing threshold current in wide bandgap lasers such as GaN lasers.

This paper discusses our newly developed technology for making GaAs/InGaAs/GaAs Tetrahedral-Shaped Recess (TSR) quantum dots. The heterostructures were grown by low-pressure MOVPE in tetrahedral-shaped recesses created on a (111) B oriented GaAs substrate using anisotropic chemical etching. We examined these structures by using cathodoluminescence (CL) measurements, and observed lower energy emissions from the bottoms of, and higher energy emissions from the walls of the TSRs. This suggests carrier confinement at the bottoms with the lowest potential energy. We carried out microanlaysis of the structures by using TEM and EDX, and found an In-rich region that had grown vertically from the bottom of the TSR with a (111)B-like bond configuration. We also measured a smaller diamagnetic shift of the lower energy photoluminecscence (PL) peak in the structure. Based on these results, we have concluded that the quantum dots are formed at the bottoms of TSRs, mainly because of the dependence of InAs composition on the local crystalline structure in this system. We also studied the lateral distribution and vertical alignment of TSR quantum dots by CL and PL measurements respectively. The advantages of TSR quantum dot technology can be summarized as follows: (i) better control in dot positioning in the lateral direction, (ii) realization of dot sizes exceeding limitations posed by lithography, (iii) high uniformity of dot size, and (iv) vertical alignment of quantum dots.