Low‐loss optical waveguides made with molecular beam epitaxial In0.012Ga0.988As and In0.2Ga0.8As‐GaAs superlattices

We demonstrate for the first time low‐loss optical guiding in In‐doped GaAs. Ridge waveguides are made with single In0.012Ga0.988As ternary layers and In0.2Ga0.8As‐GaAs superlattices. Attenuation constants of ∼1.3 dB/cm are measured and the principal loss mechanism is identified to be scattering at the ridge walls. It is expected that improved fabrication techniques will lead to guides with attenuation ≤0.5 dB/cm.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70130/2/APPLAB-48-22-1507-1.pd

Low defect densities in molecular beam epitaxial GaAs achieved by isoelectronic In doping

We have studied the effects of adding small amounts of In (0.2–1.2%) to GaAs grown by molecular beam epitaxy. The density of four electron traps decreases in concentration by an order of magnitude, and the peak intensities of prominent emissions in the excitonic spectra are reduced with increase in In content. Based on the higher surface migration rate of In, compared to Ga, at the growth temperatures it is apparent that the traps and the excitonic transitions are related to point defects. This agrees with earlier observations by F. Briones and D. M. Collins [J. Electron. Mater. 11, 847 (1982)] and B. J. Skromme, S. S. Bose, B. Lee, T. S. Low, T. R. Lepkowski, R‐Y. DeJule, G. E. Stillman, and J. C. M. Hwang [J. Appl. Phys. 58, 4702 (1985)].Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69821/2/APPLAB-49-8-470-1.pd

Material properties and optical guiding in InGaAs-GaAs strained layer superlattices--a brief review

Due to the absence of lattice-matching requirements, strained-layer superlattices offer a large tunability in bandgap and other material properties suitable for device applications. Encouraging progress has been made in the molecular-beam epitaxial and metalorganic-vapor-phase-epitaxial growth of strained-layer superlattices and in their characterization. These have been briefly reviewed here. Since a strained-layer superlattice allows the use of InxGa1-xAs layers with x-values up to ~ 1.0, a large variation of the refractive index from that in GaAs occurs due to mismatch strain and alloying. This variation in refractive index has been calculated. The increase in refractive index can be used to form optical guides in the SLS and such guides with good vertical confinement is demonstrated. Preliminary measurements of the impact-ionization parameters and deep-level traps in these materials are also reported. [alpha]/[beta] values close to and slightly greater than unity are measured. A single electron trap with thermal activation energy equal to 0.16 eV is identified.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26280/1/0000365.pd

The Repertoire of Serous Ovarian Cancer Non-genetic Heterogeneity Revealed by Single-Cell Sequencing of Normal Fallopian Tube Epithelial Cells

The inter-differentiation between cell states promotes cancer cell survival under stress and fosters non-genetic heterogeneity (NGH). NGH is, therefore, a surrogate of tumor resilience but its quantification is confounded by genetic heterogeneity. Here we show that NGH in serous ovarian cancer (SOC) can be accurately measured when informed by the molecular signatures of the normal fallopian tube epithelium (FTE) cells, the cells of origin of SOC. Surveying the transcriptomes of ∼6,000 FTE cells, predominantly from non-ovarian cancer patients, identified 6 FTE subtypes. We used subtype signatures to deconvolute SOC expression data and found substantial intra-tumor NGH. Importantly, NGH-based stratification of ∼1,700 tumors robustly correlated with survival. Our findings lay the foundation for accurate prognostic and therapeutic stratification of SOC. Using single-cell RNA sequencing, Hu et al. identify six subtypes of fallopian tube epithelium (FTE) cells in normal human fallopian tube tissues. The FTE cellular subtypes reveal intra-tumoral heterogeneity in serous ovarian cancer (SOC) and define SOC subtypes that correlate with patient prognosis.</p

Tuning microtubule dynamics to enhance cancer therapy by modulating FER-mediated CRMP2 phosphorylation

Though used widely in cancer therapy, paclitaxel only elicits a response in a fraction of patients. A strong determinant of paclitaxel tumor response is the state of microtubule dynamic instability. However, whether the manipulation of this physiological process can be controlled to enhance paclitaxel response has not been tested. Here, we show a previously unrecognized role of the microtubule-associated protein CRMP2 in inducing microtubule bundling through its carboxy terminus. This activity is significantly decreased when the FER tyrosine kinase phosphorylates CRMP2 at Y479 and Y499. The crystal structures of wild-type CRMP2 and CRMP2-Y479E reveal how mimicking phosphorylation prevents tetramerization of CRMP2. Depletion of FER or reducing its catalytic activity using sub-therapeutic doses of inhibitors increases paclitaxel-induced microtubule stability and cytotoxicity in ovarian cancer cells and in vivo. This work provides a rationale for inhibiting FER-mediated CRMP2 phosphorylation to enhance paclitaxel on-target activity for cancer therapy

Seven cases of histoplasmosis: Cutaneous and extracutaneous involvements

Seven cases of histoplasmosis have been reported, 6 males and one female. Their ages ranged from 40 to 78 years. Of 7 patients, 5 had skin lesions, 4 with palatal ulcer, one with papules and nodules. None of the patients were HIV positive. In all patients either cytology, or skin biopsy or both revealed Histoplasma. Culture was positive in two patients

Deep levels in as‐grown and Si‐implanted In0.2Ga0.8As–GaAs strained‐layer superlattice optical guiding structures

Trap levels in ∼2‐μm In0.2Ga0.8As (94 Å)/GaAs(25 Å) strained‐layer superlattices, suitable for optical waveguides, have been identified and characterized by deep‐level transient spectroscopy and optical deep‐level transient spectroscopy measurements. Several dominant electron and hole traps with concentrations ∼1014 cm−3, and thermal ionization energies ΔET varying from 0.20 to 0.75 eV have been detected. Except a 0.20‐eV electron trap, which might be present in the In0.2Ga0.8As well regions, all the other traps have characteristics similar to those identified in molecular‐beam epitaxial GaAs. Of these, a 0.42‐eV hole trap is believed to originate from Cu impurities and the others are probably related to native defects. Upon Si implantation and halogen lamp annealing, new deep centers are created. These are electron traps with ΔET=0.81 eV and hole traps with ΔET=0.46 eV. Traps occurring at room temperature may present limitations for optical devices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70879/2/JAPIAU-60-2-639-1.pd

High‐quality Si‐implanted GaAs activated by a two‐step rapid thermal annealing technique

The properties of Si‐implanted GaAs activated by halogen lamp annealing have been studied. It is found that consistently better results can be obtained by a two‐step annealing technique in which the high‐temperature main anneal step is followed by a second anneal at a lower temperature. Mobilities and activations of 4000–4600 cm2/Vs and 50–65%, respectively, are obtained for (3.0–6.5)×1012 cm−2/100 keV 29Si+ implants. These values are among the best reported for lamp‐annealed GaAs. Raman spectra confirm the high quality of the annealed crystals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71162/2/APPLAB-47-5-500-1.pd

Nature and distribution of electrically active defects in Si‐implanted and lamp‐annealed GaAs

The nature and spatial distribution of deep levels arising from defects in device‐quality, Si‐implanted, and lamp‐annealed liquid encapsulated Czochralski GaAs have been investigated. The best activation and mobility values are obtained for annealing times and temperatures of 3–5 s and 900–950 °C, respectively. Further improvements are obtained for a two‐step annealing in which a second step at 840–850 °C for 15–40 s follows the main anneal step. From Hall measurements, average layer mobilities of 4000 cm2/V s and activation of 55–65% are obtained for a Si+ dose of 6.5×1012 cm−2 at 100 keV. Electrically active deep‐level traps were studied by sensitive deep‐level transient spectroscopy (DLTS) and optical DLTS techniques. A dominant 0.57‐eV electron trap, which is also present in furnace‐annealed GaAs, originates from implantation damage and is possibly related to VGa. Additional electron traps with activation energies of 0.35 and 0.40 eV are present only in lamp‐annealed GaAs. Commonly observed hole traps have activation energies of 0.27–1.1 eV. The origins of these centers are discussed. Trap densities in single‐step lamp‐annealed samples are extremely low in comparison with furnace‐annealed samples. Typical values of NT/n are 10−2–10−4. Concentrations are even lower in samples undergoing two‐step annealing. The spatial variation of trap density seems to be principally determined by the variation of defect density in the substrate. It is apparent that high‐quality implanted and annealed GaAs can be obtained by the two‐step lamp annealing procedure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71025/2/JAPIAU-58-11-4216-1.pd