Business information systems:technology, development and management for the e-business with Webct pin card

This is an online course pack consisting of Chaffey: Business Information Systems ISBN: 027365540X and access to a Pearson Education online course ISBN: 0273673491

High-power versatile picosecond pulse generation from mode-locked quantum-dot laser diodes

This paper presents the current status of our research in mode-locked quantum-dot edge-emitting laser diodes, particularly highlighting the recent progress in spectral and temporal versatility of both monolithic and external-cavity laser configurations. Spectral versatility is demonstrated through broadband tunability and novel mode-locking regimes that involve distinct spectral bands, such as dual-wavelength mode-locking, and robust high-power wavelength bistability. Broad tunability of the pulse repetition rate is also demonstrated for an external-cavity mode-locked quantum-dot laser, revealing a nearly constant pulse peak power at different pulse repetition rates. High-energy and low-noise pulse generations are demonstrated for low-pulse repetition rates. These recent advances confirm the potential of quantum-dot lasers as versatile, compact, and low-cost sources of ultrashort pulses. © 2011 IEEE.

Temperature-dependent internal quantum efficiency of blue high-brightness light-emitting diodes

Internal quantum efficiency (IQE) of a blue high-brightness InGaN/GaN light-emitting diode (LED) was evaluated from the external quantum efficiency measured as a function of current at various temperatures ranged between 13 and 440 K. Processing the data with a novel evaluation procedure based on the ABC-model, we have determined the temperature-dependent IQE of the LED structure and light extraction efficiency of the LED chip. Separate evaluation of these parameters is helpful for further optimization of the heterostructure and chip designs. The data obtained enable making a guess on the temperature dependence of the radiative and Auger recombination coefficients, which may be important for identification of dominant mechanisms responsible for the efficiency droop in III-nitride LEDs. Thermal degradation of the LED performance in terms of the emission efficiency is also considered.

Experimentally estimated dead space for GaAs and InP based planar Gunn diodes

The authors would like to thank the staff of the James Watt Nanofabrication Centre at the University of Glasgow for help in fabricating the devices which is reported in this paper. ‘Part of this work was supported by ESPRC through EP/H011862/ 1, and EP/H012966/1.

Role of substrate quality on the performance of semipolar (11 2 - 2) InGaN light-emitting diodes

We compare the optical properties and device performance of unpackaged InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) emitting at ∼430 nm grown simultaneously on a high-cost small-size bulk semipolar (11 2 - 2) GaN substrate (Bulk-GaN) and a low-cost large-size (11 2 - 2) GaN template created on patterned (10 1 - 2) r-plane sapphire substrate (PSS-GaN). The Bulk-GaN substrate has the threading dislocation density (TDD) of ∼ and basal-plane stacking fault (BSF) density of 0 cm-1, while the PSS-GaN substrate has the TDD of ∼2 × 108cm-2 and BSF density of ∼1 × 103cm-1. Despite an enhanced light extraction efficiency, the LED grown on PSS-GaN has two-times lower internal quantum efficiency than the LED grown on Bulk-GaN as determined by photoluminescence measurements. The LED grown on PSS-GaN substrate also has about two-times lower output power compared to the LED grown on Bulk-GaN substrate. This lower output power was attributed to the higher TDD and BSF density.

Five channel WDM communication using a single a:SiC-H double pin photo device

Amorphous SiC heterostructures built as a double pin device has a non linear spectral gain which is a function of the signal wavelength that impinges on its front or back surface. Illuminating the device with several single wavelength data channels in the visible spectrum allows for Wavelength Division Multiplexing (WDM) digital communication. Using fixed ultra-violet illumination at the front or back surfaces enables the recovery of the multiplexed channels. Five channels, each using a single wavelength which is modulated by a Manchester coded signal at 12,000 bps, form a frame with 1024 bits with a preamble for signal intensity and synchronisation purposes. Results show that the clustering of the received signal enables the successful recovery of the five channel data using the front and back illumination of the surfaces of the double pin photo device. (C) 2015 Elsevier B.V. All rights reserved.

COMPREHENSIVE ELECTRICAL/OPTICAL/THERMAL CHARACTERIZATIONS OF HIGH POWER LIGHT EMITTING DIODES AND LASER DIODES

Thermal characterizations of high power light emitting diodes (LEDs) and laser diodes (LDs) are one of the most critical issues to achieve optimal performance such as center wavelength, spectrum, power efficiency, and reliability. Unique electrical/optical/thermal characterizations are proposed to analyze the complex thermal issues of high power LEDs and LDs. First, an advanced inverse approach, based on the transient junction temperature behavior, is proposed and implemented to quantify the resistance of the die-attach thermal interface (DTI) in high power LEDs. A hybrid analytical/numerical model is utilized to determine an approximate transient junction temperature behavior, which is governed predominantly by the resistance of the DTI. Then, an accurate value of the resistance of the DTI is determined inversely from the experimental data over the predetermined transient time domain using numerical modeling. Secondly, the effect of junction temperature on heat dissipation of high power LEDs is investigated. The theoretical aspect of junction temperature dependency of two major parameters – the forward voltage and the radiant flux – on heat dissipation is reviewed. Actual measurements of the heat dissipation over a wide range of junction temperatures are followed to quantify the effect of the parameters using commercially available LEDs. An empirical model of heat dissipation is proposed for applications in practice. Finally, a hybrid experimental/numerical method is proposed to predict the junction temperature distribution of a high power LD bar. A commercial water-cooled LD bar is used to present the proposed method. A unique experimental setup is developed and implemented to measure the average junction temperatures of the LD bar. After measuring the heat dissipation of the LD bar, the effective heat transfer coefficient of the cooling system is determined inversely. The characterized properties are used to predict the junction temperature distribution over the LD bar under high operating currents. The results are presented in conjunction with the wall-plug efficiency and the center wavelength shift.

Mastering heterostructured colloidal nanocrystal properties for light-emitting diodes and solar cells

Solution-grown colloidal nanocrystal (NC) materials represent ideal candidates for optoelectronic devices, due to the flexibility with which they can be synthesized, the ease with which they can be processed for devicefabrication purposes and, foremost, for their excellent and size-dependent tunable optical properties, such as high photoluminescence (PL) quantum yield, color purity, and broad absorption spectra up to the near infrared. The advent of surfactant-assisted synthesis of thermodynamically stable colloidal solutions of NCs has led to peerless results in terms of uniform size distribution, composition, rational shape-design and the possibility of building heterostructured NCs (HNCs) comprising two or more different materials joined together. By tailoring the composition, shape and size of each component, HNCs with gradually higher levels of complexity have been conceived and realized, which are endowed with outstanding characteristics and optoelectronic properties. In this review, we discuss recent advances in the design of HNCs for efficient light-emitting diodes (LEDs) and photovoltaic (PV) solar cell devices. In particular, we will focus on the materials required to obtain superior optoelectronic quality and efficient devices, as well as their preparation and processing potential and limitations

DLTS investigation of acceptor states in P3MeT Schottky barrier diodes

Deep Level Transient Spectroscopy (DLTS) has been used to investigate hole traps in the depletion region of Schottky barrier diodes formed from electropolymerised poly(3-methylthiophene). The capacitance transients appear to be composed of a fast and a slow component. Analysis of the slower component using the ''rate window'' technique yields isochronal differential capacitance curves that depend on temperature in the manner predicted by theory.

Influence of fabrication conditions on the electrical behaviour of polymer Schottky diodes

Evidence is presented which shows that anomalies in the I-V characteristics of Schottky diodes formed from electrodeposited poly(3-methylthiophene) are related to the time films are held under vacuum prior to deposition of the rectifying aluminium electrode. For short times (similar to 15 mins) a plateau appears in the forward bias characteristic which disappears leading to a significant voltage offset as the device ages or is driven into high forward bias.

Charge transport in poly(3-methylthiophene) schottky barrier diodes

Schottky-barrier devices were formed from electropolymerised films of poly (3-methylthiophene) (PMeT). Thermal annealing of a partially undoped film led to diodes with rectification ratios as high as 5900 at 1 V and 50,000 at 2.5 V and ideality factors slightly above 2. The temperature dependence of ac loss tangent and forward currents are identical suggesting that bulk effects dominate device behaviour event at very low forward voltages. Below 250 K forward currents are essentially independent of temperature. Preliminary TSC measurements show the presence of at least two trapping levels in the devices. © 1993.

Photocurrents in P3MeT Schottky barrier diodes

The photocurrent action spectrum of a Schottky diode formed from electrodeposited poly(3-methylthiophene) is shown to follow closely the UV-visible absorption spectrum. At low forward bias, the peak photocurrent asymptotes to the expected square-root dependence on total potential, V-t, across the depletion region. At high reverse bias the superlinear dependence of the photocurrent on V-t suggests that internal photoemission from the rectifying aluminium electrode may be the dominant process.

Schottky barrier diodes from semiconducting polymers

Schottky barrier diodes based on Al/poly(3-methylthiophene)/Au have been fabricated and their electrical behaviour investigated. I-V characteristics revealed a dependence on the fabrication conditions, specifically on the time under vacuum prior to evaporation of the rectifying contact and post-metal annealing at elevated temperature. The available evidence is consistent with the formation of a thin insulating layer between the metal and the polymer following these procedures. Long periods under vacuum prior to deposition of the aluminium electrode reduced the likelihood of such a layer forming. Capacitance-voltage plots of the devices were stable to voltage cycling, so long as the forward voltage did not exceed similar to 1 V. Above this a small degree of hysteresis was observed, which is attributed to the filling/emptying of interface states or traps in the polymer.