Growth and characterization of dilute bismide GaAs based alloys for high efficiency infra red laser diodes

A lot of energy in today's optical communication is wasted due to the inefficiency of optoelectronic devices operating at the telecommunication wavelength of 1.55 µm. The novel Ga(AsBi) material system is very promising to address this as it could enable the fabrication of high efficiency IR photonic devices such as laser diodes and EAM. In this work the growth of Ga(AsBi) and Ga(NAsBi) on GaAs substrates using MOVPE was investigated, and thereby MQW as well as bulk-like structures were deposited. Several growth parameters were varied systematically applying pulsed as well as continuous precursor flows. Structural analysis such as HR-XRD, AFM, SEM, (S)TEM of the crystals were performed and PL spectroscopy has been carried out. Furthermore, the first electrically pumped Ga(AsBi) containing laser diode was demonstrated. The surface of the first Ga(AsBi) samples were covered by metallic droplets consisting either of Ga, Bi or both in phase separated droplets. Drastically reducing the amounts of TMBi offer and carefully adjusting the TBAs/TEGa ratio enabled the growth of droplet free samples with measurable Bi fractions applying pulsed as well as continuous precursor flow. Bi segregates to the surface and it was found that the Bi incorporation depends on the Bi surface coverage during growth. In the case the coverage is too small, Bi only floats at the surface and does not get incorporated. At higher amounts the Bi fraction scales with the surface coverage up to a certain maximum and when it becomes too high Bi droplets begin to form. The maximum Bi fraction was found to increase with decreasing growth temperature that was varied in the range of 350 °C to 475 °C. However, at lower temperatures more defects occur and the precursor decomposition is reduced. Thus, 375 °C and 400 °C were stated to be most suitable for the MOVPE growth of Ga(AsBi) so far and maximum Bi fractions of about 7% and 5% were realized, respectively. The incorporation efficiency also increases with the growth rate and is inversely proportional to the TBAs/TEGa ratio within a range around unity were droplet free growth of Ga(AsBi) is possible. What makes the optimization and investigation of the growth conditions more complicated is that the before mentioned parameters are not independent. For example, the presence of Bi or the not fully decomposed TMBi at the surface reduces the growth rate, which is a hint that it hinders either the decomposition of the TEGa or its approach to the surface. Furthermore, lowering the growth temperature reduces the decomposition of the precursors and, hence, has an impact on the optimum TBAs/TEGa and TMBi/V ratios and reduces the growth rate. However, chemically homogenous Ga(AsBi) samples were realized and, if the subsequent layer was grown at temperatures as high as 625 °C, sharp hetero interfaces were found. The Bi floating at the surface acts as surfactant that quenches the unintentional C incorporation that usually occurs at the low applied temperatures in MOVPE and it reduces the point defect density. Hence, strong bandgap PL was found for samples that are grown in the regime at which the Bi saturation sets in. The PL peak fits perfectly to the prediction from theory with linewidths (FWHM) of about 80 to 90 meV that are related to the disorder in dilute bismides. To investigate whether the dilute bismides are suitable for optoelectronic devices, broad area Ga(AsBi) QW lasers were fabricated with Bi fractions of 2.2% and 4.4%. Electrical injection lasing of dilute bismides was demonstrated for the first time on a Ga(AsBi0.022) SQW laser with (AlGa)As barriers and cladding layers that showed room temperature lasing operation. The lowest achieved threshold current density of Ith=1.0 kA/cm² at pulsed current injection is very promising for such a new material system, however about 80% of Ith is lost by non-radiative recombination through defects. For devices with 4.4% Bi lasing was only found at low temperatures up to 180 K showing the necessity of further improving the growth of Ga(AsBi), especially when increasing the Bi fraction. For the growth of Ga(NAsBi) it was stated that at constant Bi fraction the N fraction can easily be controlled by the UDMHy supply. Samples containing up to 4% Bi and N were realized, however, it was not possible to observe room temperature PL from those structures. Hence, photo reflection measurements were carried out, showing that at constant Bi fraction the bandgap reduction due to N is about 140 meV/%N confirming that N and Bi act independently on the band structure of GaAs

Motor control retraining exercises for shoulder impingement: effects on function, muscle activation, and biomechanics in young adults

Objective: Evidence for effective management of shoulder impingement is limited. The present study aimed to quantify the clinical, neurophysiological, and biomechanical effects of a scapular motor control retraining for young individuals with shoulder impingement signs.Method: Sixteen adults with shoulder impingement signs (mean age 22 ? 1.6 years) underwent the intervention and 16 healthy participants (24.8 ? 3.1years) provided reference data. Shoulder function and pain were assessed using the Shoulder Pain and Disability Index (SPADI) and other questionnaires. Electromyography (EMG) and 3 dimensional motion analysis was used to record muscle activation and kinematic data during arm elevation to 90? and lowering in 3 planes. Patients were assessed pre and post a 10-week motor control based intervention, utilizing scapular orientation retraining.Results: Pre-intervention, patients reported pain and reduced function compared to the healthy participants (SPADI in patients 20 ? 9.2; healthy 0 ? 0). Post intervention, the SPADI scores reduced significantly (P < .001) by a mean of 10 points (?4). EMG showed delayed onset and early termination of serratus anterior and lower trapezius muscle activity pre-intervention, which improved significantly post-intervention (P < .05). Pre intervention, patients exhibited on average 4.6-7.4? less posterior tilt, which was significantly lower in 2 arm elevation planes (P < .05) than healthy participants. Postintervention, upward rotation and posterior tilt increased significantly (P <.05) during 2 arm movements, approaching the healthy values.Conclusion: A 10-week motor control intervention for shoulder impingement increased function and reduced pain. Recovery mechanisms were indicated by changes in muscle recruitment andscapular kinematics. The efficacy of the intervention requires further examined in a randomizedcontrol trial

High-quality single InGaAs/GaAs quantum dot growth on a CMOS-compatible silicon substrate for quantum photonic applications

We present the direct heteroepitaxial growth of high-quality InGaAs quantum dots on silicon, enabling scalable, cost-effective quantum photonics devices compatible with CMOS technology. GaAs heterostructures are grown on silicon via a GaP buffer and defect-reducing layers. These epitaxial quantum dots exhibit optical properties akin to those on traditional GaAs substrates, promising vast potential for the heteroepitaxy approach. They demonstrate strong multi-photon suppression with $g^{(2)}(\tau)=(3.7\pm 0.2) \times 10^{-2}$ and high photon indistinguishability $V=(66\pm 19)$% under non-resonance excitation. We achieve up to ($18\pm 1$)% photon extraction efficiency with a backside distributed Bragg mirror, marking a crucial step toward silicon-based quantum nanophotonics

Myocardial infarction primes autoreactive T cells through activation of dendritic cells

Peripheral tolerance is crucial for avoiding activation of self-reactive T cells to tissue-restricted antigens. Sterile tissue injury can break peripheral tolerance, but it is unclear how autoreactive T cells get activated in response to self. An example of a sterile injury is myocardial infarction (MI). We hypothesized that tissue necrosis is an activator of dendritic cells (DCs), which control tolerance to self-antigens. DC subsets of a murine healthy heart consisted of IRF8-dependent conventional (c) DC1, IRF4-dependent cDC2, and monocyte-derived DCs. In steady state, cardiac self-antigen alpha-myosin was presented in the heart-draining mediastinal lymph node (mLN) by cDC1s, driving the proliferation of antigen-specific CD4(+) TCR-M T cells and their differentiation into regulatory cells (Tregs). Following MI, all DC subsets infiltrated the heart, whereas only cDCs migrated to the mLN. Here, cDC2s induced TCR-M proliferation and differentiation into interleukin-(IL)-17/interferon-(IFN) gamma-producing effector cells. Thus, cardiac-specific autoreactive T cells get activated by mature DCs following myocardial infarction

Organ Specific Head Coil for High Resolution Mouse Brain Perfusion Imaging using Magnetic Particle Imaging

Magnetic Particle Imaging (MPI) is a novel and versatile imaging modality developing towards human application. When up-scaling to human size, the sensitivity of the systems naturally drops as the coil sensitivity depends on the bore diameter. Thus, new methods to push the sensitivity limit further have to be investigated to cope for this loss. In this paper a dedicated surface coil improving the sensitvity in cerebral imaging applications was developed. Similar to MRI the developed surface coil improves the sensitivity due to the closer vicinity to the region of interest. With the developed surface coil presented in this work, it is possible to image tracer samples containing only 896 pg iron and detect even small vessels and anatomical structures within a wild type mouse model. As current sensitivity measures are dependent on the tracer system a new method for determining a sensitivity measure without this dependence on the tracer is presented and verified to enable comparison between MPI receiver systems.Comment: 9 pages 7 figures original articl

Optical gain in GaAsBi/GaAs quantum well diode lasers

Electrically pumped GaAsBi/GaAs quantum well lasers are a promising new class of near-infrared devices where, by use of the unusual band structure properties of GaAsBi alloys, it is possible to suppress the dominant energy-consuming Auger recombination and inter-valence band absorption loss mechanisms, which greatly impact upon the device performance. Suppression of these loss mechanisms promises to lead to highly efficient, uncooled operation of telecommunications lasers, making GaAsBi system a strong candidate for the development of next-generation semiconductor lasers. In this report we present the first experimentally measured optical gain, absorption and spontaneous emission spectra for GaAsBi-based quantum well laser structures. We determine internal optical losses of 10–15 cm−1 and a peak modal gain of 24 cm−1, corresponding to a material gain of approximately 1500 cm−1 at a current density of 2 kA cm−2. To complement the experimental studies, a theoretical analysis of the spontaneous emission and optical gain spectra is presented, using a model based upon a 12-band k.p Hamiltonian for GaAsBi alloys. The results of our theoretical calculations are in excellent quantitative agreement with the experimental data, and together provide a powerful predictive capability for use in the design and optimisation of high efficiency lasers in the infrared