Photoluminescence study of InAlAs quantum dots grown on differently oriented surfaces

We reported the optical properties of self-assembled In0.55Al0.45As quantum dots grown by molecular beam epitaxy on (001) and (n11)A/B(n = 3,5)GaAs substrates. Two peaks were observed in the photoluminescence (PL) spectra from quantum dots in the (001) substrate and this suggested two sets of quantum dots different in size. For quantum dots in the high-index substrates, the PL spectra were related to the atomic-terminated surface (A or B substrate). The peaks for the B substrate surfaces were in the lower energy position than that for the (001) and A type. In addition, quantum dots in the B substrate have comparatively high quantum efficiency. These results suggested that high-index B-type substrate is more suitable for the fabrication of quantum dots than (001) and A-type substrates at the same growth condition. (C) 2000 American Vacuum Society. [S0734-211X(00)04701-6].

Two-dimensional ordering of self-assembled InxGal-xAs quantum dots grown on GaAs(311)B surfaces

Two-dimensional (2D) ordering of self-assembled InxGa1-xAs quantum dots (QDs) fabricated on GaAs(311)B surface by molecular beam epitaxy (MBE) are reported. The QDs are aligned into rows deferring from the direction of the misorientation of the substrate, and strongly dependent on the mole In content x of InxGa1-xAs solid solution. The ordering alignment deteriorates significantly as the In content is increased to above 0.5. The 2D ordering can be described as a centered rectangular unit mesh with the two sides parallel to [01 (1) over bar] and [(2) over bar 33], respectively. Their relative arrangement seems to be determined by a combination of the strongly repulsive elastic interaction between neighbouring islands and the minimization of the strain energy of the whole system. The ordering also helps to improve the size homogeneity of the InGaAs islands. Photoluminescence (PL) result demonstrates that QDs grown on (311)B have the narrowest linewidth and the strongest integrated intensity, compared to those grown on (100) and other high-index planes under the same condition. (C) 1999 Elsevier Science B.V. All rights reserved.

Two-dimensional ordering of self-assembled InxGa1-xAs quantum dots grown on GaAs(311)B surfaces

The two-dimensional (2D) ordering of self-assembled InxGa1-xAs quantum dots (QDs) fabricated on GaAs(3 1 1)B surface by molecular beam epitaxy (MBE) are reported. The QDs are aligned into rows differing from the direction of the misorientation of the substrate, and strongly dependent on the mole In content x of InxGa1-As-x solid solution. The ordering alignment deteriorates significantly as the In content is increased to above 0.5. The 2D ordering can be described as a centered rectangular unit mesh with the two sides parallel to [0 1 (1) over bar] and [(2) over bar 3 3], respectively. Their relative arrangement seems to be determined by a combination of the strongly repulsive elastic interaction between the neighboring islands and the minimization of the strain energy of the whole system. The ordering also helps to improve the size homogeneity of the InGaAs islands. The photoluminescence (PL) result demonstrates that QDs grown on (3 1 1)B have the narrowest linewidth and the strongest integrated intensity, compared to those on (1 0 0) and other high-index planes under the same condition. (C) 1999 Elsevier Science B.V. All rights reserved.

Photoluminescence investigation of GaInP/GaAs multiple quantum wells grown on (001) and (311) B GaAs surfaces by gas source molecular beam epitaxy

Photoluminescence (PL) investigation was carried out on GaInP/GaAs multiple quantum wells structures grown on (001) and (311) B surfaces of GaAs by gas source molecular beam epitaxy. Superlattice structures of GaAs/GaInP grown on (001) GaAs substrate were also studied in comparison. Deep-level luminescence was seen to dominate the PL spectra from the quantum wells and superlattice structures that were grown on (001) GaAs substrate. In contrast, superior optical properties were exhibited in the same structures grown on (311) B GaAs surfaces. The results suggested that GaAs/GaInP quantum well structures on (311) B oriented substrates could efficiently suppress the deep-level emissions, result in narrower PL peaks indicating smooth interfaces. (C) 1998 American Institute of Physics.

Corrugated surfaces formed on GaAs (331)a substrates: The template for laterally ordered InGaAs nanowires

Morphology evolution of high-index (331)A surfaces during molecular beam epitaxy (MBE) growth have been investigated in order to uncover their unique physic properties and fabricate spatially ordered low dimensional nanostructures. Atomic Force Microscope (AFM) measurements have shown that the step height and terrace width of GaAs layers increase monotonically with increasing substrate temperature in conventional MBE. However, this situation is reversed in atomic hydrogen-assisted MBE, indicating that step bunching is partly suppressed. We attribute this to the reduced surface migration length of Ga adatoms with atomic hydrogen. By using the step arrays formed on GaAs (331)A surfaces as the templates, we fabricated laterally ordered InGaAs self-aligned nanowires.

A multi-frame image super-resolution method

Multi-frame image super-resolution (SR) aims to utilize information from a set of low-resolution (LR) images to compose a high-resolution (HR) one. As it is desirable or essential in many real applications, recent years have witnessed the growing interest in the problem of multi-frame SR reconstruction. This set of algorithms commonly utilizes a linear observation model to construct the relationship between the recorded LR images to the unknown reconstructed HR image estimates. Recently, regularization-based schemes have been demonstrated to be effective because SR reconstruction is actually an ill-posed problem. Working within this promising framework, this paper first proposes two new regularization items, termed as locally adaptive bilateral total variation and consistency of gradients, to keep edges and flat regions, which are implicitly described in LR images, sharp and smooth, respectively. Thereafter, the combination of the proposed regularization items is superior to existing regularization items because it considers both edges and flat regions while existing ones consider only edges. Thorough experimental results show the effectiveness of the new algorithm for SR reconstruction. (C) 2009 Elsevier B.V. All rights reserved.

Gaussian diffraction model for Sb thin films in super-resolution near-field structure

SPIE

Preparation and optical property of a novel hydrophobic anti-reflection coating for KDP crystal

A novel inorganic-organic hybrid hydrophobic anti-reflection silica film used for laser crystal was obtained by sol-gel process. The film consisted of silica sols mixed with a small amount of polymethyl methacrylate (PMMA) or polystyrene (PS). The optical transparency, hydrophobic property and surface morphology of the film were characterized by UV-VIS-NIR spectrophotometer; contact angle instrument and Scanning Electron Microscopy (SEM), respectively. The results showed that the anti-reflection coating had good hydrophobility and optical transparency from 400 nm to 1200 nm. The contact angle reached to 130-140 degrees. SEM images indicated the hydrophobic films modified with PMMA or PS had compact structure compared to the pure silica sol film. (C) 2008 Elsevier B.V. All rights reserved.

Multistage etching process for microscopically smooth tellurite glass surfaces in optical fibers

Bulk samples of tellurite glass with composition 75TeO(2)-20ZnO-5Na(2)O (TZN) were fabricated by melting and quenching techniques. In order to improve the surface quality of optical fiber preform made with this tellurite glass, the authors developed a multistage etching process. The relationship between successive etching treatments and roughness of the TZN glass surface was probed by using an atomic force microscope. The results demonstrate that this multistage etching method effectively improves this tellurite glass surface smoothness to a level comparable with that of a reference silica glass slide, and the corresponding chemical micromechanisms and fundamentals are discussed and confirmed by atomic force microscopy, potentially contributing to the development of multicomponent soft glass fibers and devices. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3437017]