Electro-optic properties of GaInAsSb/GaAs quantum well for high-speed integrated optoelectronic devices

The electro-optic properties of strained GaInAsSb/GaAs quantum wells (QWs) are investigated. A single QW p-i-n sample was grown by molecular beam epitaxy with antimony (Sb) pre-deposition technique. We numerically predict and experimentally verify a strong quantum confined Stark shift of 40 nm. We also predict a fast absorption recovery times crucial of high-speed optoelectronic devices mainly due to strong electron tunneling and thermionic emission. Predicted recovery times are corroborated by bias and temperature dependent time-resolved photoluminescence measurements indicating (<= 30 ps) recovery times. This makes GaInAsSb QW an attractive material particularly for electroabsorption modulators and saturable absorbers. (C) 2013 American Institute of Physics. (http://dx.doi.org/10.1063/1.4775371

Prediction of Allogeneic Hematopoietic Stem-Cell Transplantation Mortality 100 Days After Transplantation Using a Machine Learning Algorithm: A European Group for Blood and Marrow Transplantation Acute Leukemia Working Party Retrospective Data Mining Study

PURPOSE: Allogeneic hematopoietic stem-cell transplantation (HSCT) is potentially curative for acute leukemia (AL), but carries considerable risk. Machine learning algorithms, which are part of the data mining (DM) approach, may serve for transplantation-related mortality risk prediction. PATIENTS AND METHODS: This work is a retrospective DM study on a cohort of 28,236 adult HSCT recipients from the AL registry of the European Group for Blood and Marrow Transplantation. The primary objective was prediction of overall mortality (OM) at 100 days after HSCT. Secondary objectives were estimation of nonrelapse mortality, leukemia-free survival, and overall survival at 2 years. Donor, recipient, and procedural characteristics were analyzed. The alternating decision tree machine learning algorithm was applied for model development on 70% of the data set and validated on the remaining data. RESULTS: OM prevalence at day 100 was 13.9% (n=3,936). Of the 20 variables considered, 10 were selected by the model for OM prediction, and several interactions were discovered. By using a logistic transformation function, the crude score was transformed into individual probabilities for 100-day OM (range, 3% to 68%). The model's discrimination for the primary objective performed better than the European Group for Blood and Marrow Transplantation score (area under the receiver operating characteristics curve, 0.701 v 0.646; P<.001). Calibration was excellent. Scores assigned were also predictive of secondary objectives. CONCLUSION: The alternating decision tree model provides a robust tool for risk evaluation of patients with AL before HSCT, and is available online (http://bioinfo.lnx.biu.ac.il/∼bondi/web1.html). It is presented as a continuous probabilistic score for the prediction of day 100 OM, extending prediction to 2 years. The DM method has proved useful for clinical prediction in HSCT

GaSb-based Infrared Detectors on GaAs Substrates using an Interfacial Misfit Array

Infrared detectors based on compound semiconductor technology are on the verge of outperforming HgCdTe, the leading infrared material for the past 50 years. The driving force behind this change has been the development of new detector designs based on the 6.1 � lattice constant, which includes GaSb, AlSb, and InAs binary materials. While the epitaxial deposition of these materials on GaSb substrates has enabled high performance devices, key limitations still exist. The lack of a large diameter, semi-insulating substrate; a mature, ohmic n-contact to GaSb; and a low k, large bandgap material for avalanche multiplication are all key weaknesses of this material system that further limit device development.These challenges can be met by the introduction of a new epitaxial growth mode. The growth mode, an interfacial misfit array (IMF), enables the epitaxial deposition of a high quality, relaxed GaSb epilayer on a GaAs substrate without the creation of residual threading dislocations. The IMF achieves this feat through the creation of a 90� dislocation network at the GaSb/GaAs interface, i.e. a gallium dangling bond every 14 GaAs lattice sites.In this dissertation, the structural, electrical, and optical characterization of IMF-based material and devices are all described. X-ray diffraction experiments are used to show that the dislocation network is nearly perfectly correlated, i.e. there is a 99% correlation between the location of one Lomer dislocation in the IMF network and its adjacent dislocations. Further evidence is given that the material is over 99.5% relaxed after 250 nm of growth, and continues to relax as the GaSb epilayer becomes thicker. Optical RF measurements of GaSb p-i-n homojunctions on GaAs semi-insulating substrates show that the IMF is capable of passing high frequency signals, and that the background acceptor concentration can be reduced to approximately 2 x 1016 cm-3 using Tellurium compensation doping. C-V profiles of one-sided GaAs junctions indicate that the gallium dangling bonds at the IMF interface do behave as acceptors, but that the interface charge density is 1.8E12 per sq. cm, as opposed to the Lomer dislocation density of 3E12 per sq. cm. And finally, avalanche photodiodes using the IMF interface charge are utilized to create gain in 1.55 um detectors, with both GaAs and AlGaAs multiplication regions. Low ionization coefficient ratios between holes and electrons (k values) of 0.1-0.4 are measured, indicating that the ultimate gain bandwidth product for IMF-based devices is several hundred GHz. Delta-doping is also shown to improve the optical response of the devices, without impacting the breakdown voltage or creating a commensurate increase in dark current. In short, IMF-based materials can meet the next challenges awaiting the 6.1 � material system

GaSb-based Infrared Detectors on GaAs Substrates using an Interfacial Misfit Array

Infrared detectors based on compound semiconductor technology are on the verge of outperforming HgCdTe, the leading infrared material for the past 50 years. The driving force behind this change has been the development of new detector designs based on the 6.1 � lattice constant, which includes GaSb, AlSb, and InAs binary materials. While the epitaxial deposition of these materials on GaSb substrates has enabled high performance devices, key limitations still exist. The lack of a large diameter, semi-insulating substrate; a mature, ohmic n-contact to GaSb; and a low k, large bandgap material for avalanche multiplication are all key weaknesses of this material system that further limit device development.These challenges can be met by the introduction of a new epitaxial growth mode. The growth mode, an interfacial misfit array (IMF), enables the epitaxial deposition of a high quality, relaxed GaSb epilayer on a GaAs substrate without the creation of residual threading dislocations. The IMF achieves this feat through the creation of a 90� dislocation network at the GaSb/GaAs interface, i.e. a gallium dangling bond every 14 GaAs lattice sites.In this dissertation, the structural, electrical, and optical characterization of IMF-based material and devices are all described. X-ray diffraction experiments are used to show that the dislocation network is nearly perfectly correlated, i.e. there is a 99% correlation between the location of one Lomer dislocation in the IMF network and its adjacent dislocations. Further evidence is given that the material is over 99.5% relaxed after 250 nm of growth, and continues to relax as the GaSb epilayer becomes thicker. Optical RF measurements of GaSb p-i-n homojunctions on GaAs semi-insulating substrates show that the IMF is capable of passing high frequency signals, and that the background acceptor concentration can be reduced to approximately 2 x 1016 cm-3 using Tellurium compensation doping. C-V profiles of one-sided GaAs junctions indicate that the gallium dangling bonds at the IMF interface do behave as acceptors, but that the interface charge density is 1.8E12 per sq. cm, as opposed to the Lomer dislocation density of 3E12 per sq. cm. And finally, avalanche photodiodes using the IMF interface charge are utilized to create gain in 1.55 um detectors, with both GaAs and AlGaAs multiplication regions. Low ionization coefficient ratios between holes and electrons (k values) of 0.1-0.4 are measured, indicating that the ultimate gain bandwidth product for IMF-based devices is several hundred GHz. Delta-doping is also shown to improve the optical response of the devices, without impacting the breakdown voltage or creating a commensurate increase in dark current. In short, IMF-based materials can meet the next challenges awaiting the 6.1 � material system

GaAs and AlGaAs APDs with GaSb absorption regions in a separate absorption and multiplication structure using a hetero-lattice interface

Interfacial misfit (IMF) arrays were used to create two APD structures, allowing GaSb absorption layers to be combined with wide-gap multiplication regions, grown using GaAs and Al0.8Ga0.2As, respectively. The GaAs APD represents a proof-of-principle, which is developed in the Al0.8Ga0.2As APD to achieve reduced dark currents, of 5.07 μA cm−2 at 90% of the breakdown voltage, and values for effective k = β/α below 0.2. A random-path-length (RPL) simulation was used to model the excess noise in both structures, taking into account the effects of dead space. It is envisaged that the GaSb absorption regions could be replaced with other materials from the 6.1 Å family, allowing for long-wavelength APDs with reduced dark currents and excess noise

Temperature-Dependent X-ray Diffraction Measurements of Infrared Superlattices Grown by MBE

Strained-layer superlattices (SLSs) are an active research topic in the molecular beam epitaxy (MBE) and infrared focal plane array communities. These structures undergo a &gt;500 K temperature change between deposition and operation. As a result, the lattice constants of the substrate and superlattice are expected to change by approximately 0.3%, and at approximately the same rate. However, we present the first temperature-dependent X-ray diffraction (XRD) measurements of SLS material on GaSb and show that the superlattice does not contract in the same manner as the substrate. In both InAs/InAs0.65Sb0.35 and In0.8Ga0.2As/InAs0.65Sb0.35 SLS structures, the apparent out-of-plane strain states of the superlattices switch from tensile at deposition to compressive at operation. These changes have ramifications for material characterization, defect generation, carrier lifetime, and overall device performance of superlattices grown by MBE

Absorption dynamics of type-II GaSb/GaAs quantum dots

In this paper room temperature pump-probe spectroscopy is employed to study ultrafast absorption dynamics in type-II GaSb/GaAs quantum dots (QDs). Our results identify a strong 3-5 ps timescale which is reproduced using a rate equation model and thereby associated with hole recapture by the QD following higher order absorption of part of the pump pulse into barrier layers. The strength of the component is attributed to cancelling effects in the gain and phase dynamics as a result of the carrier dependence of emission frequency that is characteristic of type-II structures.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Richard Hamilton at the Ideal Home Exhibition of 1958: gallery for a collector of brutalist and tachiste art

This essay develops a close reading of Richard Hamilton's Gallery for a Collector of Brutalist and Tachiste Art, his contribution to the Daily Mail's Ideal Home Exhibition of 1958. Included in the Gallery for a Collector was Hamilton's 1957 painting Hommage à Chrysler Corp. The essay treats both the gallery and the painting as `meta-aesthetic¿ practices that register something of the aesthetic historicity of their social and cultural moment. To demonstrate how the work relates to the historicity of perception (sensorial, social and political perception) and to the material culture of the time, the essay sets out a number of possible contexts for attending to the painting and the Ideal Home installation