Strain Engineered Electrically Pumped SiGeSn Microring Lasers on Si

SiGeSn holds great promise for enabling fully group-IV integrated photonics operating at wavelengths extending in the mid-infrared range. Here, we demonstrate an electrically pumped GeSn microring laser based on SiGeSn/GeSn heterostructures. The ring shape allows for enhanced strain relaxation, leading to enhanced optical properties, and better guiding of the carriers into the optically active region. We have engineered a partial undercut of the ring to further promote strain relaxation while maintaining adequate heat sinking. Lasing is measured up to 90 K, with a 75 K T0. Scaling of the threshold current density as the inverse of the outer circumference is linked to optical losses at the etched surface, limiting device performance. Modeling is consistent with experiments across the range of explored inner and outer radii. These results will guide additional device optimization, aiming at improving electrical injection and using stressors to increase the bandgap directness of the active material

Positive Psychology in Cancer Care: Bad Science, Exaggerated Claims, and Unproven Medicine

Claims of positive psychology about people with cancer enjoy great popularity because they seem to offer scientific confirmation of strongly held cultural beliefs and values. Our goal is to examine critically four widely accepted claims in the positive psychology literature regarding adaptational outcomes among individuals living with cancer. We examine: (1) the role of positive factors, such as a "fighting spirit" in extending the life of persons with cancer; (2) effects of interventions cultivating positive psychological states on immune functioning and cancer progression and mortality; and evidence concerning (3) benefit finding and (4) post-traumatic growth following serious illness such as cancer and other highly threatening experiences. Claims about these areas of research routinely made in the positive psychology literature do not fit with available evidence. We note in particular the incoherence of claims about the adaptational value of benefit finding and post-traumatic growth among cancer patients, and the implausibility of claims that interventions that enhance benefit finding improve the prognosis of cancer patients by strengthening the immune system. We urge positive psychologists to rededicate themselves to a positive psychology based on scientific evidence rather than wishful thinking

International meta-analysis of PTSD genome-wide association studies identifies sex- and ancestry-specific genetic risk loci

The risk of posttraumatic stress disorder (PTSD) following trauma is heritable, but robust common variants have yet to be identified. In a multi-ethnic cohort including over 30,000 PTSD cases and 170,000 controls we conduct a genome-wide association study of PTSD. We demonstrate SNP-based heritability estimates of 5–20%, varying by sex. Three genome-wide significant loci are identified, 2 in European and 1 in African-ancestry analyses. Analyses stratified by sex implicate 3 additional loci in men. Along with other novel genes and non-coding RNAs, a Parkinson’s disease gene involved in dopamine regulation, PARK2, is associated with PTSD. Finally, we demonstrate that polygenic risk for PTSD is significantly predictive of re-experiencing symptoms in the Million Veteran Program dataset, although specific loci did not replicate. These results demonstrate the role of genetic variation in the biology of risk for PTSD and highlight the necessity of conducting sex-stratified analyses and expanding GWAS beyond European ancestry populations. © 2019, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply

Tailoring the strain in Si nano-structures for defect-free epitaxial Ge over growth

We investigate the structural properties and strain state of Ge nano-structures selectively grown on Si pillars of about 60 nm diameter with different SiGe buffer layers. A matrix of TEOS SiO2 surrounding the Si nano-pillars causes a tensile strain in the top part at growth temperature of the buffer that reduces the misfit and supports a defect-free initial growth. Elastic relaxation plays the dominating role in the further increase of buffer thickness and following Ge deposition. This method leads to Ge nanostructures on Si that are free of misfit dislocations and other structural defects, which is not the case for direct Ge deposition on these pillar structures. The Ge content of the SiGe buffer is thereby not a critical parameter; it may vary over a relatively wide range

Strain and Lattice Orientation Distribution in SiN/Ge CMOS Compatible Light Emitting Microstructures by Quick X-ray Nano-diffraction Microscopy

This paper presents a study of the spatial distribution of strain and lattice orientation in CMOS-fabricated strained Ge microstripes using high resolution x-ray micro-diffraction (µ-HRXRD). The recently developed model-free characterization tool, based on a quick scanning x-ray diffraction microscopy technique can image strain down to levels of 10-5 (Δa/a)with a spatial resolution of ~0.5 µm. Strain and lattice tilt are extracted using the strain and orientation calculation software package X-SOCS. The obtained results are compared with the biaxial strain distribution obtained by lattice parameter-sensitive µ-Raman and µ-photoluminescence measurements. The experimental data are interpreted with the help of finite element modeling (FEM) of the strain relaxation dynamics in the investigated structures

Zero lattice mismatch and twin-free single crystalline ScN buffer layers for GaN growth on silicon

We report the growth of thin ScN layers deposited by plasma-assisted molecular beam epitaxy on Sc2O3/Y2O3/Si(111) substrates. Using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, we find that ScN films grown at 600 degrees C are single crystalline, twin-free with rock-salt crystal structure, and exhibit a direct optical band gap of 2.2 eV. A high degree of crystalline perfection and a very good lattice matching between ScN and GaN (misfit < 0.1%) makes the ScN/Sc2O3/Y2O3 buffer system a very promising template for the growth of high quality GaN layers on silicon

Thermoelectric Efficiency of Epitaxial GeSn Alloys for Integrated Si-Based Applications: Assessing the Lattice Thermal Conductivity by Raman Thermometry

Energy harvesting for Internet of Things applications, comprising sensing, life sciences, wearables, and communications, requires efficient thermoelectric (TE) materials, ideally semiconductors compatible with Si technology. In this work, we investigate the potential of GeSn/Ge layers, a group IV material system, as TE material for low-grade heat conversion. We extract the lattice thermal conductivity, by developing an analytical model based on Raman thermometry and heat transport model, and use it to predict thermoelectric performances. The lattice thermal conductivity decreases from 56 W/(m·K) for Ge to 4 W/(m·K) by increasing the Sn atomic composition to 14%. The bulk cubic Ge0.86Sn0.14 alloy features a TE figure of merit of ZT ∼ 0.4 at 300 K and an impressive 1.04 at 600 K. These values are extremely promising in view of the use of GeSn/Ge layers operating in the typical on-chip temperature range

Imaging structure and composition homogeneity of 300 mm SiGe virtual substrates for advanced CMOS applications by scanning X-ray diffraction microscopy

Advanced semiconductor heterostructures are at the very heart of many modern technologies, including aggressively scaled complementary metal oxide semiconductor transistors for high performance computing and laser diodes for low power solid state lighting applications. The control of structural and compositional homogeneity of these semiconductor heterostructures is the key to success to further develop these state-of-the-art technologies. In this article, we report on the lateral distribution of tilt, composition, and strain across step-graded SiGe strain relaxed buffer layers on 300 mm Si(001) wafers treated with and without chemical−mechanical polishing. By using the advanced synchrotron based scanning X-ray diffraction microscopy technique K-Map together with micro-Raman spectroscopyand Atomic Force Microscopy, we are able to establish a partial correlation between real space morphology and structuralproperties of the sample resolved at the micrometer scale. In particular, we demonstrate that the lattice plane bending of thecommonly observed cross-hatch pattern is caused by dislocations. Our results show a strong local correlation between the strain field and composition distribution, indicating that the adatom surface diffusion during growth is driven by strain field fluctuations induced by the underlying dislocation network. Finally, it is revealed that a superficial chemical mechanical polishing of cross-hatched surfaces does not lead to any significant change of tilt, composition, and strain variation compared to that of as-grown complementary metal oxide semiconductor transistors for high performance computing and laser diodes for low power solid state lighting applications. The control of structural and compositional homogeneity of these semiconductor heterostructures is the key to success to further develop these state-of-the-art technologies. In this article, we report on the lateral distribution of tilt, composition, and strain across step-graded SiGe strain relaxed bu ff er layers on 300 mm Si(001) wafers treated with and without chemical − mechanical polishing. By using the advanced synchrotron based scanning X-ray di ff raction microscopy technique K-Map together with micro-Raman spectroscopy and Atomic Force Microscopy, we are able to establish a partial correlation between real space morphology and structural properties of the sample resolved at the micrometer scale. In particular, we demonstrate that the lattice plane bending of the commonly observed cross-hatch pattern is caused by dislocations. Our results show a strong local correlation between the strain fi eld and composition distribution, indicating that the adatom surface di ff usion during growth is driven by strain fi eld fl uctuations induced by the underlying dislocation network. Finally, it is revealed that a super fi cial chemical − mechanical polishing of cross- hatched surfaces does not lead to any significant change of tilt, composition, and strain variation compared to that of as-grown sample