A high-gain (Ga,Al)As/GaAs heterostructure bipolar transistor withan equilibrium-depleted spike-doped base

The fabrication is reported of a high-gain (Ga,Al)As/GaAs heterostructure bipolar transistor (HBT) with a p-spike-doped base that is depleted at equilibrium. The device structure, based on that proposed for a bipolar inversion-channel field-effect transistor (BICFET), was grown by molecular-beam epitaxy (MBE). Fabricated transistors, containing an AlAs/n-GaAs superlattice emitter layer, exhibited DC current gains of up to 500. Maximum current gains of tested devices occurred at collector current densities in the mid-10³ A cm ^-2 range. It is postulated that the induced base in these transistors is formed predominantly by the forward-bias action on the base-emitter junction     

Lateral protrusions of ohmic contacts to AlGaAs/GaAs MODFET material

Cross-sectional transmission electron microscopy is used to determine the structure of Au-, Ge- and Ni-based ohmic contacts at the interface with AlGaAs/GaAs modulation-doped field-effect-transistor material. Significant lateral diffusion (?0.12?m) is found to occur at the edge of the contact during alloying. The observed contact structure places a limit on minimum geometries and must be taken into account if accurate device modelling is to be carried out.     

Interaction of Silicon Nitride and Metal Surfaces

An Mn-Fe-rich slag forms near the tips of Si₃N₄-based indexible cutting tools during the machining of cast iron. Manganese and iron were found to react chemically with Si₃N₄ to form a liquid phase in the presence of air, but not in the absence of air, at temperatures comparable to those reached during machining operations. Thus, chemical reactions between Fe, Mn, Si₃N₄, and O₂ may be a factor in the wear of Si₃N₄ tools against cast iron.     

PROCESSING AND PERFORMANCE OF SEVERAL SiC WHISKER-REINFORCED Al2O3 MATRIX COMPOSITES

The influence of different SiC whiskers on the processing and performance of Al₂O₃ matrix composites were investigated. Three types of commercial SiC whiskers produced in the United States were used. The composites contained 30 v/o of SiC whisker and were consolidated by both hot pressing (HP) and hot pressing followed by hot isostatic pressing (HP/HIP) techniques. The microstructure, mechanical properties, fracture behavior and toughening mechanisms of the composites were evaluated. The results show that the whisker types and processing techniques have profound effect on the densification and the properties of the composites.     

Effect of sintering additives on the behaviour of SiC whisker-reinforced Si3N4 composites

The effects of sintering additives on the microstructural development, whisker stability, oxidation resistance and room-temperature mechanical properties of the SiC whisker-reinforced Si₃N₄ matrix composites were investigated. Seven different combinations of Y₂O₃ and Al₂O₃ were used as sintering additives. The composites containing 20 vol % SiC whiskers were densified by hot pressing. The microstructure of the resulting composites was characterized using X-ray diffraction, scanning and transmission electron microscopy. Oxidation testing of the composite at 1400 °C was conducted to investigate the relationship between matrix compositions and oxidation resistance. The flexural strength, fracture toughness and crack propagation patterns were also characterized and correlated with the microstructural features.     

Processing and Microstructural Development of In Situ TiN-Reinforced Silicon Nitride/Silicon Oxynitride Composites

The development of a novel TiN-reinforced silicon nitride/silicon oxynitride composite using an innovative in situ TiN-forming technique was investigated. Silicon powder compacts containing various amounts of TiO₂ (anatase structure) and sintering additives were nitrided under N₂ atmosphere and then further densified by hot pressing. The microstructure of the resultant composite was analyzed by X-ray diffraction, scanning electron microscopy, and solid-state nuclear magnetic resonance spectroscopy. The results of this study show that TiO₂ can be successfully converted to TiN during the nitridation of Si + TiO₂ mixture. The TiO₂ content affects not only the microstructure of the matrix but also the composition of the intergranular phase. The type and amount of sintering additives also show a significant effect on the microstructural development of the composite.     

Displacement reactions in the solid state

Simple displacement reactions in the solid state are considered with the purpose of predict-ing the morphologies and the reaction rates from a knowledge of pertinent thermodynamic and diffusion data. The theoretical predictions are substantiated by experimental observa-tions for four reaction couples [Ni/Cu₂O, Co/Cu₂O, Fe/Cu₂O, and Fe/NiO] reacted at 1000°C. Displacement reactions are classified according to the product morphology; layered and ag-gregate arrangements of the product phases were observed, with two modifications (lamellar and interwoven) occurring within the aggregate morphological class. Parabolic kinetics for the growth of the product phases are observed for each couple. The magnitudes of the para-bolic rate constants for the couples which exhibit the layered arrangement are comparable with calculated values. A technique for controlling the product morphology is discussed, and a process for producing porous metal or oxide screens is introduced.     

Properties of Si3N4 Produced by Nitriding Slip-Cast Si Containing Si3N4 Grog Additions

The properties of Si₃N₄ compositions produced by nitriding slip-cast Si bodies containing up to 16% Si₃N₄ grog were determined. The introduction of grog consistently lowered the densities, the room- and high-temperature strengths, and the resistance to oxidation. The open structure of the grog-containing mixes favored low-temperature gas-phase reactions leading to α-Si₃N₄ formation. In higher-density compositions containing predominantly Si, gas-liquid-solid reactions at higher temperatures produced a relatively greater content of the β phase.     

Effect of ethyl acetate addition on phase stability,octane number and volatility criteria of ethanol-gasoline blends

Blending ethanol in gasoline causes problems related to volatility and phase stability of the fuel blends. Ethanol is completely miscible with water so it has high affinity to water that may be present in storage tanks or that formed due to humidity. Drop in ambient temperature influences the stability of ethanol-gasoline blends and causes phase separation to the blend. This phase separation cause disadvantages like: poor quality fuel, loss in cost, and damage to storage tanks and engine parts due to corrosion. In this work, Ethanol-blended gasolines E5, E10, E15, E20 and ethanol-free gasoline (E0) were formulated to study the effects of ethyl acetate addition on these fuels. The obtained results revealed that the addition of ethyl acetate to ethanol-gasoline blends has many advantages such as enhancing the stability of the fuel blends and improving octane number with no adverse impacts on the volatility criteria of the investigated fuel blends.     

Double heterojunction bipolar transistor in Al/sub x/Ga/sub 1-x/As/GaAs/sub 1-y/Sb/sub y/ system

Double heterojunction bipolar transistors based on the Al/sub x/Ga/sub 1-x/As/GaAs/sub 1-y/Sb/sub y/ system are examined. The base layer consists of narrow band gap GaAs/sub 1-y/Sb/sub y/ and the emitter and collector consist of wider band gap Al/sub x/Ga/sub 1-x/As. Preliminary experimental results show that AlGaAs/GaAsSb/GaAs DHBTs exhibit a current gain of five and a maximum collector current density of 5*10/sup 4/ A/cm/sup 2/.<>