Sharp line emission spectra from GaAs FET like structures

Magneto-optical analysis of prominent photoluminescence lines from GaAs FET structures has been performed. Fifteen samples were investigated. Each consisted of a sulfur doped active layer on a high resistivity buffer layer (both epitaxially grown films) on a chromium doped GaAs substrate. The active layers were generally 2μm thick or less, except for two thicker layers (4 and 5μm) grown especially for this study. Buffer layer thicknesses ranged from 1.5 to 26μm. A model based on carrier diffusion through the active layer has been used to interpret the spectra as originating from the active-buffer interface region. All spectra contain strong-evidence of two donorbound exciton complexes associated with sulfur (1.51417eV) and silicon (1.51412eV). Other sharp spectral features included up to six lines associated with more complicated complexes. Linear Zeeman and quadratic diamagnetic behavior of the lines in applied magnetic fields are discussed. Supported under AF Contract F33615-77-C-5003 Supported under AF Contract F33615-76-C-1207     

Ten-inch molecular beam epitaxy production system for HgCdTe growth

Growth of Hg_1−xCd_xTe by molecular beam epitaxy (MBE) has been under development since the early 1980s at Rockwell Scientific Company (RSC), formerly the Rockwell Science Center; and we have shown that high-performance and highly reproducible MBE HgCdTe double heterostructure planar p-on-n devices can be produced with high throughput for various single- and multiplecolor infrared applications. In this paper, we present data on Hg_1−xCd_xTe epitaxial layers grown in a ten-inch production MBE system. For growth of HgCdTe, standard effusion cells containing CdTe and Te were used, in addition to a Hg source. The system is equipped with reflection high energy electron diffraction (RHEED) and spectral ellipsometry in addition to other fully automated electrical and optical monitoring systems. The HgCdTe heterostructures grown in our large ten-inch Riber 49 MBE system have outstanding structural characteristics with etch-pit densities (EPDs) in the low 10⁴ cm⁻² range, Hall carrier concentration in low 10¹⁴ cm⁻³, and void density <1000 cm². The epilayers were grown on near lattice-matched (211)B Cd_0.96Zn_0.04Te substrates. High-performance mid wavelength infrared (MWIR) devices were fabricated with R₀A values of 7.2×10⁶ Ω-cm² at 110 K, and the quantum efficiency without an antireflection coating was 71.5% for cutoff wavelength of 5.21 μm at 37 K. For short wavelength infrared (SWIR) devices, an R₀A value of 9.4×10⁵ Ω-cm² at 200 K was obtained and quantum efficiency without an antireflection coating was 64% for cutoff wavelength of 2.61 μm at 37 K. These R₀A values are comparable to our trend line values in this temperature range.     

Defect clusters in neutron-irradiated vanadium containing oxygen

Single crystal samples of high-purity vanadium containing 95, 300, and 500 wt ppm oxygen were irradiated at 95°C in the Ames Laboratory Research Reactor to a dose of 1.4 x 10¹⁹ neutrons/cm² (E > 1 MeV). The density and size distribution of radiation-produced defect clusters were analyzed by transmission electron microscopy in as-irradiated and post-irradiation-annealed material. The defect cluster density was observed to increase with increasing oxygen concentration and the average defect cluster size to decrease. Upon post-irradiation annealing the density decreased and the average size increased, but higher annealing temperatures were required for higher oxygen material. The results are discussed in terms of the nucleation of defect clusters at oxygen atoms and small oxygen-atom aggregates. The increased stability against annealing of higher oxygen vanadium is believed to be due to the greater segregation of oxygen at the defect clusters.     

Colorimetric determination of sterols in vegetable oils with chloramine T and sulfuric acid reagent

A new colorimetric method for determination of sterols in vegetable oils using chloramine T and conc sulfuric acid reagent is described. After saponification of oils, the sterols present in the unsaponifiable matter are separated by thin layer chromatography (TLC) on Silica Gel G plates in the solvent system ethyl ether/petroleum ether (40–60 C) (1:1). The sterols are treated with 1% chloramine T in cone H₂SO₄ at 100 C for 12 min to develop the yellowish-brown color which is read at 400 nm. Sterol content is calculated against a cholesterol standard. The method is at least 5 times more sensitive than that which uses Liebermann-Burchard reagent; color formed is stable for 48 hr.     

Structure and properties of acrylonitrile-[(2-methacryloyloxy)alkoxy]trimethyl silane copolymers

Dielectric, x-ray diffraction, density, thermomechanical, and thermogravimetric studies on polyacrylonitrile (PAN), poly[acrylonitrile-(2 methacryloyloxy)ethoxytrimethylsilane] [poly(AN-2MAETMS)], and poly[acrylonitrile-(2 methacryloyloxy)propoxytrimethylsilene] [poly(AN-2MAPTMS)] copolymers have been carried out for investigating their structure. The glass transition temperature as indicated from the dielectric and thermomechanical analysis data are lower for the copolymers as compared to PAN. Crystallinity is influenced by the introduction of the silylated acrylic comonomer units but the crystalline lattice remains similar to that of PAN. The changes obseved in the various properties of these coplymers clearly suggest a more closely packed structure of poly(AN-2MAETMS) than poly(AN-2MAPTMS), and the uninterrupted PAN sequences are longer in the former. Thermal stability of copolymers has also been investigated.     

Plasma insulin and growth hormone during antarctic residence

A 50-year-old female developed a swelling in the epigastrium which later ruptured to form a sinus. A diagnosis of primary cutaneous cryptococcosis was made with the help of histopathology and microbiological studies. Treatment with amphotericin-B and 5-flucytosine gave a good therapeutic response and the sinus healed within 2 months.     

A new N-type doping precursor for MOCVD-IMP growth of detector quality MCT

A new indium precursor, triisopropyl indium (TIPIn), has been used for doping MCT at low carrier concentrations. Previous attempts using indium organometallics resulted in a strong memory effect where residual doping would persist for many growth runs. Introducing TIPIn on the tellurium inject line resulted in a similarly strong memory doping but this was not observed when feeding the dopant in on the cadmium injection line. The TIPIn is believed to have been forming a low volatility adduct with diisopropyl tellurium (DIPTe) in the feed line and to have continued to evaporate at a low but significant rate. By keeping the TIPIn and DIPTe precursors separate until they entered the reactor, the desired low 10¹⁵ cm⁻³ carrier concentration and flat indium profiles could be achieved with good reproducibility. Good electrical characteristics were measured for these layers with Auger limited lifetime >1 μs at 77K.