Synthesis of MDMO-PPV capped PbS quantum dots and their application to solar cells

Poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) capped PbS quantum dots about 3-6 nm in diameter were synthesized with a novel method. Unlike the synthesis of oleic acid capped PbS quantum dots, the reactions were carried out in solution at room temperature, with the presence of a capping ligand species, MDMO-PPV. The quantum dots were used to fabricate bulk heterojunction solar cells with an indium tin oxide (ITO)/polyethylenedioxythiophene/polystyrenesulphonate (PEDOT: PSS)/MDMO-PPV: PbS/Al structure. Current density-voltage characterization of the devices showed that after the addition of the MDMO-PPV capped PbS quantum dots to MDMO-PPV film, the performance was dramatically improved compared with pristine MDMO-PPV solar cells. (C) 2008 Elsevier Ltd. All rights reserved.

Broadband Emitting Superluminescent Diodes With InAs Quantum Dots in AlGaAs Matrix

Superluminescent diodes were fabricated by using InAs-AlGaAs self-assembled quantum dots (QDs) as the active region. The ultrawide emitting spectrum of 142 nm was achieved. The short migration length of indium adatoms on AlGaAs surface increases the size dispersion of InAs QDs, resulting in the broadening of optical gain spectrum.

Investigation on the structural origin of n-type conductivity in InN films

This work presents a study of the correlation between the electrical properties and the structural defects in nominally undoped InN films. It is found that the density of edge-type threading dislocations (TDs) considerably affects the electron concentration and mobility in InN films. The Hall-effect measured electron concentration increases, while the Hall mobility decreases with the increase in the edge-type TD density. With the combination of secondary ion mass spectrometry and positron annihilation analysis, we suggest that donor-type point defects at the edge-type TD lines may serve as dominant donors in InN films and affect the carrier mobility.

Organic light-emitting diodes with magnesium doped CuPc as an efficient electron injection layer

Bright organic electroluminescent devices are developed using a metal-doped organic layer intervening between the cathode and the emitting layer. The typical device structure is a glass substrate/indium-tin oxide (ITO)/copper phthalocyanine (CuPc)/NN'-bis-(1-naphthl)-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB)/Tris(8-quinolinolato) aluminum(Alq(3))/Mg-doped CuPc/Ag. At a driving voltage of 11 V, the device with a layer of Mg-doped CuPc (1:2 in weight) shows a brightness of 4312 cd/m(2) and a current efficiency of 2.52 cd/A, while the reference device exhibits 514 cd/m(2) and 1.25 cd/A.

Optimization of metamorphic InGaAs quantum wells on GaAs grown by molecular beam epitaxy

We investigate the molecular beam epitaxy growth of metamorphic InxGa(1-x)As materials (x up to 0.5) on GaAs substrates systematically. Optimization of structure design and growth parameters is aimed at obtaining smooth surface and high optical quality. The optimized structures have an average surface roughness of 0.9-1.8 nm. It is also proven by PL measurements that the optical properties of high indium content (55%) InGaAs quantum wells are improved apparently by defect reduction technique and by introducing Sb as a surfactant. These provide us new ways for growing device quality metamorphic structures on GaAs substrates with long-wavelength emissions.

Lattice polarity detection of InN by circular photogalvanic effect

We report an effective and nondestructive method based on circular photogalvanic effect (CPGE) to detect the lattice polarity of InN. Because of the lattice inversion between In- and N-polar InN, the energy band spin splitting is opposite for InN films with different polarities. Consequently under light irradiation with the same helicity, CPGE photocurrents in In- and N-polar layers will have opposite directions, thus the polarity can be detected. This method is demonstrated by our CPGE measurements in both n- and p-type InN films.

Mn-AlInN: a new diluted magnetic semiconductor

Mn ions have been incorporated into MOCVD grown Al1-x In (x) N/GaN thin films by ion implantation to achieve the room temperature ferromagnetism in the samples. Magnetic characterizations revealed the presence of two ferromagnetic transitions one has Curie points at similar to 260 K and the other above room temperature. In-diffusion of indium caused by the Mn implantation leads to the partition of AlInN epilayer into two diluted magnetic semiconductor sub-layers depending on the Mn concentration. The Curie temperature of 260 K is assigned to the layer having lower concentration, whereas T (c) above room temperature is assumed to be associated to the layer having higher Mn concentration.

Well-Aligned Zn-Doped InN Nanorods Grown by Metal-Organic Chemical Vapor Deposition and the Dopant Distribution

We report the synthesis and characterization of Zn-doped InN nanorods by metal-organic chemical vapor deposition. Electron microscopy images show that the InN nanorods are single-crystalline structures and vertically well-aligned. Energy-dispersive X-ray spectroscopy analyses suggest that Zn ions are distributed nonhomogenously in InN nanorods. Simulations based on diffusion model show that the doping concentration along the radial direction of InN nanorod is bowl-like from the exterior to the interior, the doping concentration decreases, and Such dopant distribution result in a bimodal EDXS spectrum of Zn across the nanorod. The study of the mechanism of doping effect is useful for the design of InN-based nanometer devices. Also, high-quality Zn-doped InN nanorods will be very attractive as building blocks for nano-optoelectronic devices.'

The application of SnS nanoparticles to bulk heterojunction solar cells

Tin mono-sulphide (SnS) nanoparticles were synthesized by a facile method. Reactions producing narrow size distribution SnS nanoparticles with the diameter of 5.0-10 nm were carried out in an ethylene glycol solution at 150 degrees C for 24 h. Bulk heterojunction solar cells with the structure of indium tin oxide (ITO)/polyethylenedioxythiophene polystyrenesulphonate (PEDOT PSS)/SnS polymer/Al were fabricated by blending the nanoparticles with a conjugated polymer to form the active layer for the first time. Current density-voltage characterization of the devices showed that due to the addition of SnS nanoparticles to the polymer film, the device performance can be dramatically improved, compared with that of the pristine polymer solar cells. (c) 2009 Published by Elsevier B.V.

A mini-staged multi-stacked quantum cascade laser for improved optical and thermal performance

In this paper, a mini-staged multi-stacked quantum cascade laser structure with a designed wavelength of 4.7 mu m is presented. By introducing five 0.5 mu m thick high thermal conductivity InP interbuffer layers, the 60-stages active region core of the quantum cascade laser is divided into six equal parts. Based on simulation, this kind of quantum cascade laser with a 10 mu m ridge width gives nearly circular two-dimensional far-field distribution (FWHM = 32.8 degrees x 29 degrees) and good beam quality parameters M-2 = 1.32 x 1.31 in the fast axis (growth direction) and the slow axis (lateral direction). Due to the enhancement of lateral heat extraction through the interbuffer layers, compared to the conventional structure, a decrease of about 5-6% for the maximum temperature in the active region core of the mini-staged multi-stacked quantum cascade laser with indium-surrounded and gold-electroplated packaging profiles is obtained at all possible dissipated electrical power levels.

Inductively coupled plasma etching in fabrication of 2D InP-based photonic crystals

The authors developed an inductively coupled plasma etching process for the fabrication of hole-type photonic crystals in InP. The etching was performed at 70 degrees C using BCl3/Cl-2 chemistries. A high etch rate of 1.4 mu m/min was obtained for 200 nm diameter holes. The process also yields nearly cylindrical hole shape with a 10.8 aspect ratio and more than 85 degrees straightness of the smooth sidewall. Surface-emitting photonic crystal laser and edge emitting one were demonstrated in the experiments.

Determination of wurtzite InN/cubic In2O3 heterojunction band offset by x-ray photoelectron spectroscopy

In2O3 is a promising partner of InN to form InN/In2O3 heterosystems. The valence band offset (VBO) of wurtzite InN/cubic In2O3 heterojunction is determined by x-ray photoemission spectroscopy. The valence band of In2O3 is found to be 1.47 +/- 0.11 eV below that of InN, and a type-I heterojunction with a conduction band offset (CBO) of 0.49-0.99 eV is found. The accurate determination of the VBO and CBO is important for use of InN/In2O3 based electronic devices.

Fine structural splitting and exciton spin relaxation in single InAs quantum dots

We have studied the exciton spin dynamics in single InAs quantum dots (QDs) with different exciton fine structural splitting (FSS) by transient luminescence measurements. We have established the correlation between exciton spin relaxation rate and the energy splitting of the FSS when FSS is nonzero and found that the spin relaxation rate in QD increases with a slope of 8.8x10(-4) ns(-1) mu eV(-1). Theoretical analyses based on the phonon-assisted relaxations via the deformation potential give a reasonable interpretation of the experimental results.

The synthesis of MDMO-PPV capped PbS nanorods and their application in solar cells

Poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) capped PbS nanorods about 100 nm in diameter and 400 nm in length were synthesized via a hydrothermal route in toluene and dimethylsulfoxide solution. By blending the PbS nanorods with the MDMO-PPV as the active layer, bulk heterojunction solar cells with an indium tin oxide (ITO)/polyethylenedioxythiophene/polystyrenesulphonate (PEDOT PSS)/MDMO-PPV PbS nanorods/Al structure were fabricated in a N-2 filled glove box, Current density-voltage characterization of the devices showed that the solar cells with PbS nanorods hybrid with MDMO-PPV as active layer were better in performance than the devices with the polymer only. (C) 2009 Elsevier B.V. All rights reserved.

Annealing behaviors of long-wavelength InAs/GaAs quantum dots with different growth procedures by metalorganic chemical vapor deposition

The effects of annealing on the optical properties of InAs/GaAs quantum dots (QDs) grown under different conditions by metalorganic chemical vapor deposition (MOCVD) are studied. A lower QD growth rate leads to an earlier and faster decrease of QD photoluminescence (PL) intensity with increasing annealing temperature. which is proposed to be related to the increased QD two-dimensional (2D)-three-dimensional (3D) transition critical layer thickness at low QD growth rate. High-quality GaAs cap layers grown at high temperature and a low deposition rate are shown to decrease the blueshift of the QDs' emission wavelength significantly during in-situ I h annealing experiments, which is important for the fabrication of long-wavelength InAs/GaAs QD lasers by MOCVD technique. (C) 2009 Elsevier B.V. All rights reserved.