Progress of Si-based nanocrystalline luminescent materials

Si-based nanomaterials are some new photoeletronic and informational materials developed rapidly in recent years, and they have potential applications in the light emitting devices, e. g. Si light emitting diode, Si laser and integrated Si-based photoelectronics. Among them are nano-scale porous silicon (ps), Si nanocrystalline embedded SiO2 (SiOx, x < 2.0) matrices, Si nanoquantum dot and Si/SiO2 superlattice, etc. At present, there are various indications that if these materials can achieve efficient and stable luminescence, which are photoluminescence (PL) and electroluminescence (EL), it is possible for them to lead to a new informational revolution in the early days of the 21st century. In this article, we will mainly review the progress of study on Si-based nanomaterials in the past ten years. The involved contents are the fabricated methods, structural characterizations and light emitting properties. Finally, we predicate the developed tendency of this field in the following ten years.

Highly coherent solid-state quantum bit from a pair of quantum dots

In this letter, we propose a scheme to buildup a highly coherent solid-state quantum bit (qubit) from two coupled quantum dots. Quantum information is stored in the state of the electron-hole pair with the electron and hole located in different dots, and universal quantum gates involving any pair of qubits are realized by effective coupling interaction via virtually exchanging cavity photons. (C) 2002 American Institute of Physics.

Photoluminescence and capacitance transients in highly Mg-doped GaN

Behaviors of the photoluminescence blue-band and near-bandgap peak and the relevant thermal ionization energies of the shallow and deep Mg-related acceptors have been studied, respectively. The 2.989 eV blue-band is attributed to the deep donor-acceptor-pair transitions involving a deep Mg-related acceptor at E-v+0.427 eV. The blueshift with increasing excitation power is explained by variation in the contribution of close and distant donor-acceptor-pairs to the luminescence. The redshift with increasing temperature results from thermal release of carriers from close donor-acceptor-pairs. The 3.26 eV near-bandgap peak is attributed to the shallow donor-acceptor-pair transitions involving a shallow Mg-related acceptor at E-v+0.223 eV. The relevant thermal ionization energies of the shallow and deep Mg-related acceptors, being about E-v+0.16 and E-v+0.50eV, are determined from deep-level transient Fourier spectroscopy measurements.

Subband electron properties of highly doped InAlAs/InGaAs metamorphic high-electron-mobility transistors on GaAs substrates

A Shubnikov-de Haas (SdH) oscillation measurement was performed on highly doped InAlAs/InGaAs metamorphic high-electron-mobility transistors on GaAs substrates at a temperature of 1.4 K. By analyzing the experimental data using fast Fourier transform, the electron densities and mobilities of more than one subband are obtained, and an obvious double-peak structure appears at high magnetic field in the Fourier spectrum. In comparing the results of SdH measurements, Hall measurements, and theoretical calculation, we found that this double-peak structure arises from spin splitting of the first-excited subband (i=1). Very close mobilities of 5859 and 5827 cm(2)/V s are deduced from this double-peak structure. The sum of the carrier concentration of all the subbands in the quantum well is only 3.95x10(12) cm(-2) due to incomplete transfer of the electrons from the Si delta -doped layer to the well. (C) 2001 American Institute of Physics.

Blue-violet photoluminescence from large-scale highly aligned boron carbonitride nanofibers

We report on the strong blue-violet photoluminescence (PL) at room temperature from the large-scale highly aligned boron carbonitride (BCN) nanofibers synthesized by bias-assisted hot filament chemical vapor deposition. The photoluminescence peak wavelength shifts in the range of 470-390 nm by changing the chemical composition of the BCN nanofibers, which shows an interesting blue and violet-light-emitting material with adjustable optical properties. The mechanism for the shift of the PL peaks at room temperature is also discussed. (C) 2000 American Institute of Physics. [S0003-6951(00)04427-2].

Fabrication of luminescent Ge nanocrystals started from unlayered hydrogenated amorphous SiGe films or hydrogenated amorphous Si hydrogenated amorphous Ge multilayers

Nanocrystalline Ge embedded in SiOx matrix is fabricated by oxidizing hydrogenated amorphous Sice alloys or hydrogenated amorphous Si/hydrogenated amorphous Ge multilayers. The structures before and after oxidation are systematically investigated. Visible light emission was observed from both samples. The luminescence peak is located at 2.2 eV which is independent of the starting materials. Compared to the luminescence from unlayered samples, the photoluminescence spectrum from multilayered samples has a narrower band width, which can be attributed to the uniform size distribution. The light emission origin is also discussed briefly and a mechanism different from the quantum size effect is suggested.

New method for the growth of highly uniform quantum dots

A new method is realized for the growth of self-formed quantum dots. We identify that dislocation-free islands can be formed by the strain from the strained superlattice taken as a whole. Unlike the Stranski-Krastanow (S-K) growth mode, the islands do not form during the growth of the corresponding strained single layers. Highly uniform quantum dots can be self-formed via this mechanism. The low temperature spectra of self-formed InGaAs/GaAs quantum dot superlattices grown on a (001) GaAs substrate have a full width at half maximum of 26-34 meV, indicating a better uniformity of quantum dot size than those grown in the S-K mode. This method can provide great degrees of freedom in designing possible quantum dot devices. 1998 Published by Elsevier Science B.V. All rights reserved.

Effects of growth temperature on highly mismatched InAs grown on GaAs substrates by MBE

InAs layers were grown on GaAs by molecular beam epitaxy (MBE) at substrate temperature 450 and 480 degrees C, and the surface morphology was studied with scanning electron microscopy (SEM). We have observed a high density of hexagonal deep pits for samples grown at 450 degrees C, however, the samples grown at 480 degrees C have smooth surface. The difference of morphology can be explained by different migration of cations which is temperature dependent. Cross-sectional transmission electron microscopy (XTEM) studies showed that the growth temperature also affect the distributions of threading dislocations in InAs layers because the motion of dislocations is kinetically limited at lower temperature. (C) 1998 Elsevier Science B.V. All rights reserved.

Highly efficient and tunable microlasers on photonic crystal slab

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Highly efficient and stable organic light-emitting diodes employing MoO3-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride as hole injection layer

We report highly efficient and stable organic light-emitting diodes (OLEDs) with MoO3-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride (PTCDA) as hole injection layer (HIL). A green OLED with structure of ITO/20 wt% MoO3: PTCDA/NPB/Alq(3)/LiF/Al shows a long lifetime of 1012 h at the initial luminance of 2000 cd/m(2), which is 1.3 times more stable than that of the device with MoO3 as HIL. The current efficiency of 4.7 cd/A and power efficiency of 3.7 lm/W at about 100 cd/m(2) have been obtained. The charge transfer complex between PTCDA and MoO3 plays a decisive role in improving the performance of OLEDs.

Blue Luminescent Properties of Silicon Nanowires Grown by a Solid-Liquid-Solid Method

Silicon nanowires (SiNWs) were grown directly from n-(111) single-crystal silicon (c-Si) substrate based on a solid-liquid-solid mechanism, and Au film was used as a metallic catalyst. The room temperature photoluminescence properties of SiNWs were observed by an Xe lamp with an exciting wavelength of 350 nm. The results show that the SiNWs exhibit a strongly blue luminescent band in the wavelength range 400-480 nm at an emission peak position of 420 nm. The luminescent mechanism of SiNWs indicates that the blue luminescence is attributed to the oxygen-related defects, which are in SiOx amorphous oxide shells around the crystalline core of SiNWs.

Radiation forces of a highly focused radially polarized beam on spherical particles

A radially polarized beam focused by a high-numerical-aperture (NA) objective has a strong longitudinal and nonpropagating electric field in the focal region, which implies that it is suitable for axial optical trapping. In this paper, we use the vectorial diffraction integral to represent the field distribution of the radially polarized beam focused by a high-NA objective and then employ the T-matrix method to compute the radiation forces on spherical particles. Effects of different parameters, such as the size of the sphere, the inner radius of the radially polarized beam, and the NA of the objective, on the radiation forces are presented.