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This paper reports on laser excitation power dependent photoluminescence (PL) studies on epitaxial GaAs1−xBix (2.3% < x < 10.4%) layers with thicknesses of 30–40 nm which are compressively strained onto GaAs substrates. Such materials when used as optical active regions in semiconductor lasers offer the possibility of suppressing the efficiency-limiting Auger recombination losses and improving laser performance in the telecommunication range (1.3–1.5 μm). These experimental investigations on GaAsBi allow us to verify the extent to which GaAs1−xBix provides the optimised band structure as predicted, and secondly to provide the first evidence of the influence of this band structure on optical efficiency and carrier recombination processes. An analysis of the dependence of PL intensity on excitation power was employed to identify the recombination mechanisms in GaAs1−xBix alloys. Temperature tuning the samples with bismuth concentration ~ 8.5% and 1.4% provides tentative evidence for the suppression of Auger recombination losses in this material system highlighting its potential for efficient telecoms laser applications. [ABSTRACT FROM AUTHOR]

We report angle dependent and temperature dependent (9 K-300 K) photo-modulated reflectance (PR) studies on vertical-cavity surface-emitting laser (VCSEL) structures, designed for 2.3 µm mid-infrared gas sensing applications. Changing the temperature allows us to tune the energies of the quantum well (QW) transitions relative to the VCSEL cavity mode (CM) energy. These studies show that this VCSEL structure has a QW-CM offset of 21meV at room temperature. Consequently the QW ground-state transition comes into resonance with the CM at 220 ± 2 K. The results from these PR studies are closely compared with those obtained in a separate study of actual operating devices and show how the PR technique may be useful for device optimisation without the necessity of having first to process the wafers into working devices. [ABSTRACT FROM AUTHOR]

The GaBixAs1-x bismide III-V semiconductor system remains a relatively underexplored alloy particularly with regards to its detailed electronic band structure. Of particular importance to understanding the physics of this system is how the bandgap energy Eg and spin-orbit splitting energy Δo vary relative to one another as a function of Bi content, since in this alloy it becomes possible for Δo to exceed Eg for higher Bi fractions, which occurrence would have important implications for minimising non-radiative Auger recombination losses in such structures. However, this situation had not so far been realised in this system. Here, we study a set of epitaxial layers of GaBixAs1-x (2.3% ≤ x ≤ 10.4%), of thickness 30-40 nm, grown compressively strained onto GaAs (100) substrates. Using room temperature photomodulated reflectance, we observe a reduction in Eg, together with an increase in Δo, with increasing Bi content. In these strained samples, it is found that the transition energy between the conduction and heavy-hole valence band edges is equal with that between the heavy-hole and spin-orbit split-off valence band edges at ∼9.0 ± 0.2% Bi. Furthermore, we observe that the strained valence band heavy-hole/light-hole splitting increases with Bi fraction at a rate of ∼15 (±1) meV/Bi%, from which we are able to deduce the shear deformation potential. By application of an iterative strain theory, we decouple the strain effects from our experimental measurements and deduce Eg and Δo of free standing GaBiAs; we find that Δo indeed does come into resonance with Eg at ∼10.5 ± 0.2% Bi. We also conclude that the conduction/valence band alignment of dilute-Bi GaBiAs on GaAs is most likely to be type-I. [ABSTRACT FROM AUTHOR]

In this report, we provide an x-ray magnetic circular dichroism (XMCD) study for 100 nm thick epitaxial magnetite (Fe3O4) films on MgO (001) and Al2O3 (0001) substrates. For XMCD, we recorded the surface sensitive total electron yield and the bulk sensitive transmission spectra. From the analysis of the XMCD data, we find an increased Fe spin moment (10% larger) at the surface of the film on MgO (100) with respect to the corresponding bulk value of the film. Surface and bulk spin moments of the film on Al2O3(0001) are almost equal. For both films, the bulk orbital to spin moments ratio increases from zero at 70 K to 0.03–0.04 at 300 K. For Fe3O4/MgO (001), the surface orbital to spin moment ratio behaves similarly to the bulk value, while the orbital to spin moments ratio is increased at the Fe3O4/Al2O3 (0001) surface to 0.06. The observed differences between films grown on MgO and Al2O3 are explained within the framework of differences in mismatch strain experienced by the films. [ABSTRACT FROM AUTHOR]

The article examines modulation speed and leakage current in 650 nm resonant-cavity light emitting diodes (RCLED). It discusses how the RCLED bandwidth varies with device size and investigates the influence of different carrier recombination processes on the modulation rate. In particular, using bandwidth measurements in conjunction with a drift-diffusion model, the article quantifies the influence of the mono-molecular and radiative recombination processes in terms of their contribution to the total injected current.

The Ga(AsBi) material system opens opportunities in the field of high efficiency infrared laser diodes. We report on the growth, structural investigations, and lasing properties of dilute bismide Ga(AsBi)/(AlGa)As single quantum well lasers with 2.2% Bi grown by metal organic vapor phase epitaxy on GaAs (001) substrates. Electrically injected laser operation at room temperature is achieved with a threshold current density of 1.56 kA/cm2 at an emission wavelength of ∼947 nm. These results from broad area devices show great promise for developing efficient IR laser diodes based on this emerging materials system. [ABSTRACT FROM AUTHOR]

We investigate the temperature and pressure dependence of the light-current characteristics and electroluminescence spectra of GaAs1-xBix/GaAs light emitting diodes. The temperature dependence of the emission wavelength shows a relatively low temperature coefficient of emission peak shift of 0.19 ± 0.01 nm/K. A strong decrease in emission efficiency with increasing temperature implies that non-radiative recombination plays an important role on the performance of these devices. The pressure coefficient of the GaAs0.986Bi0.014 bandgap is measured to be 11.8 ± 0.3 meV/kbar. The electroluminescence intensity from GaAsBi is found to decrease with increasing pressure accompanied by an increase in luminescence from the GaAs cladding layers suggesting the presence of carrier leakage in the devices. [ABSTRACT FROM AUTHOR]

We have investigated the solid state reaction at the interface of Co2Cr0.6Fe0.4Al, Co2FeSi, and Ni2MnGa Heusler alloy films and Al cap layers using x-ray absorption spectroscopy in transmission and total electron yield mode. At elevated temperatures and at rough surfaces the deposited Al severely reacts with the surface of a Heusler alloy indicated by changes of the absorption spectra. Microspectroscopy using photoemission electron microscopy reveals that the reaction proceeds inhomogeneously with reaction nuclei separated on a micron length scale. [ABSTRACT FROM AUTHOR]

In this letter the authors present a comprehensive study of the threshold current and its temperature dependence in GaAsSb-based quantum well edge-emitting lasers for emission at 1.3 μm. It is found that at room temperature, the threshold current is dominated by nonradiative recombination accounting for more than 90% of the total threshold current density. From high hydrostatic pressure dependence measurements, a strong increase in threshold current with pressure is observed, suggesting that the nonradiative recombination process may be attributed to electron overflow into the GaAs/GaAsP barrier layers and, to a lesser extent, to Auger recombination. [ABSTRACT FROM AUTHOR]

We present a combination of spectroscopy and device measurements on GaAsSb/GaAs vertical-cavity surface-emitting laser (VCSEL) structures to determine the temperature at which the wavelength of the VCSEL cavity mode (CM) aligns with that of the quantum well (QW) ground-state transition (GST), and therefore the gain peak. We find that, despite the achievement of room temperature (RT) continuous wave lasing in VCSEL devices, the QW transition and the CM are actually slightly misaligned at this temperature; room temperature electroluminescence measurements from a cleaved edge of the VCSEL wafer indicate that the 300 K QW GST energy is at 0.975 ± 0.005 eV, while the CM measured in the VCSEL surface reflectivity spectra is at 0.9805 ± 0.0002 eV. When the wafer sample is cooled, the CM and QW GST can be brought into alignment at 270 ± 10 K, as confirmed by temperature-dependent electro-modulated reflectance (ER) and edge-electroluminescence spectroscopic studies. This alignment temperature is further confirmed by comparing the temperature dependence of the emission energy of a fabricated VCSEL device with that of an edge-emitting laser structure with a nominally identical active region. The study suggests that for further device improvement, the room temperature CM and QW GST energies should be more closely matched and both designed to a smaller energy of about 0.95 eV, somewhat closer to the 1.31 μm target. The study amply demonstrates the usefulness of non-destructive ER characterisation techniques in VCSEL manufacturing with GaAsSb-based QWs. [ABSTRACT FROM AUTHOR]

This paper reports on progress in the development of GaAsBi/(Al)GaAs based lasers grown using metal-organic vapour phase epitaxy and focuses on the underlying processes governing their efficiency and temperature dependence. Room temperature lasing has been achieved in devices with 2.2% Bi and lasing in devices with 4.4% Bi was observed up to 180 K. We show that the device performance can be improved by optimizing both electrical and optical confinement in the laser structures. Analysis of the temperature dependence of the threshold current together with pure spontaneous emission and high hydrostatic pressure measurements indicate that device performance is currently dominated by non-radiative recombination through defects (>80% of the threshold current at room temperature in 2.2% Bi samples) and that to further improve the device performance and move towards longer wavelengths for optical telecommunications (1.3–1.5 µm) further effort is required to improve and optimize material quality. [ABSTRACT FROM AUTHOR]

We investigate the temperature and pressure dependence of the threshold current density of edge-emitting GaAsSb/GaAs quantum well (QW) lasers with different device characteristics. Thermally activated carrier leakage via defects is found to be very sensitive to the growth conditions of GaAsSb QWs. An optimization of the growth conditions reduces the nonradiative recombination mechanisms from 93% to 76% at room temperature. This improvement in carrier recombination mechanisms leads to a large improvement in the threshold current density from 533 Acm-2/QW to 138 Acm-2/QW and the characteristic temperature, T0 (T1), from 51 ± 5 K (104 ± 16 K) to 62 ± 2 K (138 ± 7 K) near room temperature. [ABSTRACT FROM AUTHOR]

Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, Eg, and spin-orbit splitting, ΔSO, respectively. The possibility of achieving ΔSO > Eg and a reduced temperature (T) dependence for Eg are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure Eg(x, T) and ΔSO (x, T) in In0.53Ga0.47BixAs1-x/InP samples for 0 ≤ x ≤ 0.039 by various complementary optical spectroscopic techniques. While we find no clear evidence of a decreased dEg/dT (≈0.34 ± 0.06 meV/K in all samples) we find ΔSO > Eg for x > 3.3-4.3%. The predictions of a valence band anti-crossing model agree well with the measurements. [ABSTRACT FROM AUTHOR]

An abstract of the article "A machine classification measure of meditation ability," by A. McCollough, K. Hild, H. Wabeh, and B. Oken is presented.