Simulated [111] Si-SiGe terahertz quantum cascade laser

The prospect of developing a silicon laser has long been an elusive goal, mainly due to the indirect band gap and large effective carrier masses. We present a design for a terahertz intersubband laser grown on the [111] crystal plane and simulate performance using a rate equation method including scattering due to alloy disorder, interface roughness, carrier-phonon and Coulombic interactions. We predict gain greater than 40 cm-1 and a threshold current density of 70 A/cm2

The importance of electron temperature in silicon-based terahertz quantum cascade lasers

Quantum cascade lasers (QCLs) are compact sources of coherent terahertz radiation. Although all existing QCLs use III-V compound semiconductors, silicon-based devices are highly desirable due to the high thermal conductivity and mature processing technology. We use a semiclassical rate-equation model to show that Ge/SiGe THz QCL active region gain is strongly enhanced by reducing the electron temperature. We present a bound-to-continuum QCL design employing L-valley intersubband transitions, using high Ge fraction barriers to reduce interface roughness scattering, and a low electric field to reduce the electron temperature. We predict a gain of similar to 50 cm(-1), which exceeds the calculated waveguide losses. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3237177

Substrate orientation and alloy composition effects in n-type SiGe quantum cascade structures

We show using a theoretical self-consistent effective mass/rate equation approach that n-type SiGe-based quantum cascade lasers are potentially made viable by either using the (111) orientation or a Ge-rich substrate

Design of Ge/SiGe quantum-confined Stark effect electroabsorption heterostructures for CMOS compatible photonics

We describe a combined 6×6 k.p and one-band effective mass modelling tool to calculate absorption spectra in Ge–SiGe multiple quantum well (MQW) heterostructures. We find good agreement with experimentally measured absorption spectra of Ge–SiGe MQW structures described previously in the literature, proving its predictive capability, and the simulation tool is used for the analysis and design of electroabsorption modulators. We employ strain-engineering in Ge–SiGe MQW systems to design structures for modulation at 1310 nm and 1550 nm

Synthesis and binding studies of novel sigma receptor ligands

Abstract only availableSigma receptors are binding sites that are found in the brain, in the endocrine and immune systems, and also in the lungs, kidneys, intestines, muscles and especially the liver. They are classified into two subtypes, sigma1 and sigma2, both of which have unique characteristics. Sigma receptors in the central nervous system are thought to be involved in disorders such as psychoses, Alzheimer's disease, and schizophrenia. A number of human tumors also show high densities of sigma receptors. In this study, three novel compounds were synthesized with the intent of characterizing how their structural differences affect affinity for the sigma1 and sigma2 receptors. We investigated derivatives of a potent sigma1 selective agonist, 1-(3',4'-dimethoxyphenethyl)-4-(3''-phenyl propyl)piperazine, developed by Santen Pharmaceutical Co. Specifically, the 4'-methoxy moiety was replaced by benzyloxy, phenethyloxy and 3-phenylpropyloxy substituents. These were prepared by reaction of the corresponding 4'-phenol with base and treatment with phenethyl bromide, 3-phenylpropyl bromide or benzyl bromide. For the phenethyl and 3-phenylpropyl derivatives, a mixture of 40% KOH and tetrabutylammonium hydroxide (1M in MeOH) was used as the base. Column chromatography provided these target compounds in 81 - 94% purified yields. The benzyl derivative proved difficult to obtain using this procedure, and different conditions were used to synthesize this compound. The 4'-phenol was reacted with benzyl bromide and potassium carbonate in ethanol to give the benzyl ether in 35% yield after purification by column chromatography. All three compounds were characterized by 1H NMR, and were analyzed by elemental analysis and HPLC. Currently, competition receptor binding studies are being run on the synthesized compounds to measure their affinities for sigma1 and sigma2 receptors.NSF-REU/NIH Program in Radiochemistr

Comparing Online and Offline Knowledge Networks of Carbon Capture and Storage

© 2017 The Authors. This paper examines the complex ecosystem of organisations involved in the proposed role out of carbon capture and storage (CCS) in the UK. Through analysis of interview and twitter data, it focuses on the flow of knowledge flows within online and offline networks, highlighting how in this case, CCS retains a niche audience, with communication and information flows concentrated with industry and stakeholder networks at a local and regional scale, as opposed to reaching broader national policy makers, and the wider publics. This brings a unique insight into the construction of networks across intersecting sectors of this critical technology and highlights how for successful implementation CCS, actors may need to reach out beyond their existing network

Si/SiGe bound-to-continuum quantum cascade emitters

Si/SiGe bound-to-continuum quantum cascade emitters designed by self-consistent 6-band k.p modeling and grown by low energy plasma enhanced chemical vapour deposition are presented demonstrating electroluminescence between 1.5 and 3 THz. The electroluminescence is Stark shifted by an electric field and demonstrates polarized emission consistent with the design. Transmission electron microscopy and x-ray diffraction are also presented to characterize the thick heterolayer structure

Experiences of intensive home treatment for a mental health crisis during the perinatal period: A UK qualitative study

Some women with severe perinatal mental health difficulties in England are cared for by acute home treatment services, known as Crisis Resolution Teams (CRTs), which provide short-term home-based treatment for adults experiencing a mental health crisis. Intensive home treatment has been trialed in a number of countries, but it is not known how well suited it is to the needs of perinatal women. This qualitative study aimed to explore how women and practitioners experience the provision of intensive home treatment for perinatal mental health problems. Semi-structured interviews were conducted with women who had received intensive home treatment in the perinatal period (n = 15), and focus groups were held with practitioners working in CRTs or in specialist perinatal mental health services (3 groups, n = 25). Data were analysed thematically. Women commonly found intensive home treatment problematic, experiencing it as intrusive and heavily risk-focused, with poor staff continuity and little tailoring to the perinatal context. However, women valued emotional support when provided, particularly when it had a perinatal focus, sometimes based on practitioners sharing their own experiences. Some women also appreciated avoiding hospital admission, but choice was often limited. Practitioners reported a lack of perinatal training among CRT staff and described difficulties tailoring treatment to perinatal women's needs. Currently, intensive home treatment, as offered by CRTs, may not be well suited to women with perinatal mental health difficulties. Findings suggest a need to develop community crisis responses that are better tailored to the needs of this population

Effects of rapid thermal annealing on device characteristics of InGaAs/GaAs quantum dot infrared photodetectors

In this work, rapid thermal annealing was performed on InGaAs/GaAs quantum dot infrared photodetectors (QDIPs) at different temperatures. The photoluminescence showed a blueshifted spectrum in comparison with the as-grown sample when the annealing temperature was higher than 700 °C, as a result of thermal interdiffusion of the quantum dots (QDs). Correspondingly, the spectral response from the annealed QDIP exhibited a redshift. At the higher annealing temperature of 800 °C, in addition to the largely redshifted photoresponse peak of 7.4 µm (compared with the 6.1 µm of the as-grown QDIP), a high energy peak at 5.6 µm (220 meV) was also observed, leading to a broad spectrum linewidth of 40%. This is due to the large interdiffusion effect which could greatly vary the composition of the QDs and thus increase the relative optical absorption intensity at higher energy. The other important detector characteristics such as dark current, peak responsivity, and detectivity were also measured. It was found that the overall device performance was not affected by low annealing temperature, however, for high annealing temperature, some degradation in device detectivity (but not responsivity) was observed. This is a consequence of increased dark current due to defect formation and increased ground state energy. © 2006 American Institute of Physic