Photostability of single-photon emission from a single quantum dot in the 650-nm wavelength band at room temperature

The photoluminescence correlation from a single CdSe nanocrystal under pulsed excitation is studied, and a single photon is realized at wavelength 655 nm at room temperature. The single colloidal CdSe quantum dot is prepared on a SiO2/silicon surface by a drop-and-drag technique. The long-term stability of the single-photon source is investigated; it is found that the antibunching effect weakens with excitation time, and the reason for the weakening is attributed to photobleaching. The lifetimes of photoluminescence from a single quantum dot are analyzed at different excitation times. By analyzing the probability distribution of on and off times of photoluminescence, the Auger assisted tunneling and Auger assisted photobleaching models are applied to explain the antibunching phenomenon.

The effect of single AlGaN interlayer on the structural properties of GaN epilayers grown on Si (111) substrates

High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single AlGaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si (111) substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlGaN interlayer on the structural proper-ties of the resulting GaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AlGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.

Study on the perfection of in situ P-injection synthesis LEC-InP single crystals

Undoped, S-doped and Fe-doped InP crystals with diameter up to 4-inch have been pulled in drop 10 0 drop -direction under P-rich condition by a rapid P-injection in situ synthesis liquid encapsulated Czochralski (LEC) method. High speed photoluminescence mapping, etch-pit density (EPD) mapping and scanning electron microscopy have been used to characterize the samples of the single crystal ingots. Dislocations and electrical homogeneity of these samples are investigated and compared. By controlling the thermal field and the solid-liquid interface shape, 4-inch low-EPD InP single crystals have been successfully grown by the rapid P-injection synthesis LEC method. The EPD across the wafer of the ingots is less than 5 x 10(4) cm(-2). Cluster defects with a pore center are observed in the P-rich LEC grown InP ingots. These defects are distributed irregularly on a wafer and are surrounded by a high concentration of dislocations. The uniformity of the PL intensity across the wafer is influenced by these defects. (C) 2004 Elsevier B.V. All rights reserved.

Analog-digital and digital-analog converters using single-electron and MOS transistors

This paper proposes two kinds of novel single-electron analog-digital conversion (ADC) and digital-analog conversion (DAC) circuits that consist of single-electron transistors (SETs) and metal-oxide-semiconductor (MOS) transistors. The SET/MOS hybrid ADC and DAC circuits possess the merits of the SET circuit and the MOS circuit. We obtain the SPICE macro-modeling code of the SET transistor by studying and fitting the characteristics of the SET with SPICE simulation and Monte Carlo simulation methods. The SPICE macro-modeling code is used for the simulation of the SET/MOS hybrid ADC and DAC circuits. We simulate the performances of the SET/MOS hybrid 3-b ADC and 2-b DAC circuits by using the H-SPICE simulator. The simulation results demonstrate that the hybrid circuits can perform analog-digital and digital-analog data conversion well at room temperature. The hybrid ADC and DAC circuits have advantages as-follows: 1) compared with conventional circuits, the architectures of the circuits are simpler; 2) compared with single electron transistor circuits, the circuits have much larger load capability; 3) the power dissipation of the circuits are lower than uW; 4) the data conversion rate of the circuits can exceed 100 MHz; and 5) the resolution of the ADC and DAC circuits can be increased by the pipeline architectures.

Nucleation of diamond by pure carbon ion bombardment - a transmission electron microscopy study

A cross-sectional high-resolution transmission electron microscopy (HRTEM) study of a film deposited by a 1 keV mass-selected carbon ion beam onto silicon held at 800 degrees C is presented. Initially, a graphitic film with its basal planes perpendicular to the substrate is evolving. The precipitation of nanodiamond crystallites in upper layers is confirmed by HRTEM, selected area electron diffraction, and electron energy loss spectroscopy. The nucleation of diamond on graphitic edges as predicted by Lambrecht [W. R. L. Lambrecht, C. H. Lee, B. Segall, J. C. Angus, Z. Li, and M. Sunkara, Nature, 364 607 (1993)] is experimentally confirmed. The results are discussed in terms of our recent subplantation-based diamond nucleation model. (c) 2005 American Institute of Physics.

Synthesis of GaN nanotip triangle pyramids on 3C-SiC epilayer/Si substrates via an in situ In-doping technique

GaN nanotip triangle pyramids were synthesized on 3C-SiC epilayer via an isoelectronic In-doping technique. The synthesis was carried out in a specially designed two-hot-boat chemical vapor deposition system. In (99.999%) and molten Ga (99.99%) with a mass ratio of about 1:4 were used as the source, and pieces of Si (111) wafer covered with 400-500 nm 3C-SiC epilayer were used as the substrates. The products were analyzed by x-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, Raman spectroscopy, and photoluminescence measurements. Our results show that the as-synthesized GaN pyramids are perfect single crystal with wurtzite structure, which may have potential applications in electronic/photonic devices.

Measurement of single electron spin with submicron Hall magnetometer

Submicron Hall magnetometry has been demonstrated as an efficient technique to probe extremely weak magnetic fields. In this letter, we analyze the possibility of employing it to detect single electron spin. Signal strength and readout time are estimated and discussed with respect to a number of practical issues. (C) 2005 American Institute of Physics.

Numerical study of a high-resolution far-field scanning optical microscope via a surface plasmon-modulated light source

In this paper, we analyze light transmission through a single subwavelength slit surrounded by periodic grooves in layered films consisting of An and dielectric material. A subwavelength grating is scanned numerically by the finite difference time domain method in two dimensions. The results show that the transmission field can be confined to a spot with subwavelength width in the far field and can be useful in the application of a high-resolution far-field scanning optical microscope.

Metal catalysis-free, direction-controlled planar growth of single-crystalline alpha-Si3N4 nanowires on Si(100) substrate

Single-crystalline alpha-Si3N4 nanowires are controlled to grow perpendicular to the wet-etched trenches in the SiO0.94 film on the plane of the Si substrate without metal catalysis. A detailed characterization is carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photoluminescence at 600 nm from alpha-Si3N4 nanowires is attributed to the recombination at the defect state formed by the Si dangling bond N3 equivalent to Si-center dot. The growth mechanism is considered to be related to the catalysis and nitridation of SiO nanoclusters preferably re-deposited around the inner corner of the trenches, as well as faster Si diffusion along the slanting side walls of the trenches. This simple direction-controlled growth method is compatible with the CMOS process, and could facilitate the fabrication of alpha-Si3N4 nanoelectronic or nanophotonic devices on the Si platform.

Quantum trajectory analysis for electrical detection of single-electron spin resonance

A Monte Carlo simulation on the basis of quantum trajectory approach is carried out for the measurement dynamics of a single-electron spin resonance. The measured electron, which is confined in either a quantum dot or a defect trap, is tunnel coupled to a side reservoir and continuously monitored by a mesoscopic detector. The simulation not only recovers the observed telegraphic signal of detector current, but also predicts unique features in the output power spectrum which are associated with electron dynamics in different regimes.

Near-field scanning optical microscopy with an active probe

A near-field scanning optical microscopy (NSOM) system employing a very-small-aperture laser (VSAL) as an active probe is reported in this Letter. The VSAL in our experiment has an aperture size of 300 nmx300 nm and a near-field spot size of about 600 nm. The resolution of the NSOM system with the VSAL can reach about 600 nm, and even 400 nm. Considering the high output power of the VSAL, such a NSOM system is a potentially useful tool for nanodetection, data storage, nanolithography, and nanobiology.

Ground-state properties of an artificial molecule: a simple model calculation for the double quantum dot

The ground state of a double quantum-dot structure is studied by a simplified Anderson-type model. Numerical calculations reveal that the ground-state level of this artificial molecule increases with the increasing single particle level of the dot, and also increases with the decreasing transfer integrals. We show the staircase feature of the electron occupation and the properties of the ground-state eigenvector by varying the;single particle level of the dot.

HIGH-RESOLUTION DLTS AND ITS APPLICATION TO LATTICE-MISMATCH-INDUCED DEEP LEVELS IN INGAP

A new method of differentiating the deep level transient spectroscopy (DLTS) signal is used to increase the resolution of conventional DLTS. Using this method, more than one single deep level with small differences in activation energy or capture cross section, which are often hard to determine by conventional DLTS, can be distinguished. A series of lattice-mismatched InxGa1-xP samples are measured by improved DLTS to determine accurately the activation energy of a lattice-mismatch-induced deep level. This level cannot be clearly determined using conventional DLTS because the two signals partly overlap each other. Both the signals are thought to originate from a phosophorus vacancy and lattice-mismatch-induced defect.

A transmission electron microscopy study of microstructural defects in proton implanted silicon

The microstructure of silicon on defect layer, a new type of silicon-on-insulator material using proton implantation and two-step annealing to obtain a high resistivity buried layer beneath the silicon surface, has been investigated by transmission electron microscopy. Implantation induced a heavily damaged region containing two types of extended defects involving hydrogen: {001} platelets and {111} platelets. During the first step annealing, gas bubbles and {111} precipitates formed. After the second step annealing, {111} precipitates disappeared, while the bubble microstructure still remained and a buried layer consisting of bubbles and dislocations between the bubbles was left. This study shows that the dislocations pinning the bubbles plays an important role in stabilizing the bubbles and in the formation of the defect insulating layer. (C) 1996 American Institute of Physics.

X-ray diffraction study of GaAs/InAs/GaAs ultrathin single quantum well

Ultrathin single quantum well (about one monolayer) grown on GaAs(001) substrate with GaAs cap layer has been studied by high resolution x-ray diffractometer on a beamline of the Beijing Synchrotron Radiation Facility. The interference fringes on both sides of the GaAs(004) Bragg peak are asymmetric and a range of weak fringes in the higher angle side of the Bragg peak is observed. The simulated results by using the kinematical diffraction method shows that the weak fringe range appears in the higher angle side when the phase shift introduced by the single quantum well is very slightly smaller than m pi (m:integer), and vice versa. After introducing a reasonable model of single quantum well, the simulated pattern is in good agreement with the experiment. (C) 1996 American Institute of Physics.