Design and process development of a novel multi-wafer OMVPE reactor for growing very uniform GaAs and AlGaAs epitaxial layers

A unique multi-wafer OMVPE reactor with capability to produce atomic-layer abrupt-ness is demonstrated. Uniform GaAs and AlGaAs epitaxial layers were grown on four two-inch wafers or one three- or four-inch wafer. Thickness variation across a three-inch wafer was less than ±2%, while the variation of Al solid composition was less than ±1%. Multiple AlGaAs/GaAs quantum wells ranging in size from 10Å to 140Å were grown with heterointerface roughness less than one monolayer. The electrical properties of HEMT device were studied. Variations of sheet carrier concentration and electron mobility were ±6% and ±5% respectively across a three-inch wafer. The carrier con-centration profile, mobility spectrum and device characteristics of DH-HEMT are also presented. These results indicate that this OMVPE reactor can grow good device struc-tures for microwave and millimeter-wave power device applications.     

Liquid phase epitaxy of pbtese lattice-matched to pbsnte

The conditions for liquid phase epitaxial growth of lead telluride selenide on lead tin telluride are presented, and some physical and electrical properties of the epilayers grown are described. The composition and energy gap of the quaternary lead salt compound, lead tin telluride selenide, lattice-matched to lead selenide and to lead-tin telluiride, as determined from published data, is also presented. The growth of PbSnTeSe on PbSnTe is demonstrated.     

Comparison between microwave and thermal curing of glass fiber–epoxy composites: Effect of microwave‐heating cycle on mechanical properties

The objective of this study was to compare the mechanical properties between epoxy composites cured by thermal heating and microwave heating. Epoxy‐anhydride resins reinforced with glass fiber were cured in a domestic microwave oven and in a thermal oven. Hardening agents included methyl tetrahydrophthalic anhydride and methyl hexahydrophthalic anhydride. Microwave curing was carried out at various conditions, including 1‐, 2‐, and 3‐step heating cycle, whereby each cycle employed different power level and time. Mechanical properties were tested according to ASTM standards. It is found that the microwave‐cured composites produced mechanical properties as good as the thermally cured composites. The 2‐ and 3‐step heating cycle used in the microwave curing process produced better mechanical properties higher than those obtained from the microwaved 1‐step and thermally curing process. This is attributed to the slow increase in temperature during the beginning of the microwave curing process whereby the very low power level was applied in the first cycle of the multistep heating process. This affected the slower rate of viscosity increment, resulting in better wettability of the glass fiber with enhanced interfacial adhesion between the fibers and the resins. The viscosity of resins affected the homogeneity of the crosslinked structure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1059–1070, 2006     

Effect of growth temperature on the photoluminescent spectra of undoped AlGaAs grown by metalorganic-chemical vapor deposition

A detailed investigation of the effect of substrate growth temperature on the optical properties of AlGaAs grown by metalorganic-chemical vapor deposition is reported, using room- and low-temperature photoluminescence. A monotonie increase in band-to-band photoluminescence is observed as the growth temperature is increased from 700 to 800°C. At the same time, however, an increase in the incorporation of C and Ge acceptors is observed.     

Duties and Responsibilities of Construction Managers: Perceptions of Parties Involved in Construction

This paper reports the findings of a study conducted by researchers at Illinois Institute of Technology under the direction and supervision of the ASCE Committee on Management Practices in Construction to investigate the expectations of the parties involved in the construction process, including designers, owners, general contractors, subcontractors, construction managers, and educators, relative to construction managers’ duties. The findings suggest that while there is some consensus among parties to a construction project relative to CM duties particularly in the construction phase, there is also some disagreement, most of which appear to be between contractors and designers. Most disagreements are related to CM duties performed in the bidding and postconstruction phases of projects.