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Notes: We fabricated superlattice modulation-doped field-effect transistors where the doping is concentrated in GaAs narrow quantum wells separated by undoped AlGaAs barriers. As the doped AlGaAs regions are eliminated from such a structure, the concentration of traps generally associated with doping of AlGaAs is low. We observed the threshold voltage shift of only 140 mV with temperature change from 77 to 300 K (which should be compared to the shift of 200–300 mV in conventional modulation-doped field-effect transistors). Peak transconductances of 310 mS/mm at 300 K and 321 mS/mm at 77 K have been obtained. An interesting feature of this device is the complicated dependence of the transconductance on the gate voltage which has two peaks at 77 K and one sharp peak at 300 K. These peaks are caused by the parallel conduction paths in the superlattice at high gate voltages and by the gate leakage current. This parallel conduction in GaAs-doped quantum wells may be used in order to achieve larger voltage swings in superlattice modulation-doped field-effect transistors.

Notes: We propose the mechanism of the mobility enhancement in highly doped semiconductor quantum wells, based on the large increase in the carrier concentration using the field effect and on the corresponding reduction of the ratio of the ionized impurity concentration to the electron concentration. We observe the mobility enhancement in GaAs quantum wells doped at ∼2×1018 cm−3 at 77 K from 572 cm2/V s under the equilibrium conditions to approximately 2500 cm2/V s when a large carrier concentration is induced into the quantum well in a field-effect transistor. This effect can be used to increase the voltage and current swing in modulation-doped structures and may also allow us to achieve the mobility enhancement in new semiconductor materials with inherently large defect densities.

Notes: We have used pulsed laser annealing to promote and characterize highly localized chemical reactions at Al interfaces with III-V compound semiconductors. At successive stages of these laser-induced reactions, we have monitored atomic movement and chemical structure on a microscopic scale using soft x-ray photoemission spectroscopy and Auger electron spectroscopy. For Al on each of the six III-V compound semiconductors investigated, we have found a finite range of energy density above a characteristic threshold energy density such that a chemical reaction is produced without disrupting the surface morphology. The systematic change of threshold with different semiconductors indicates a thermally activated reaction occurring in the molten phase of the Al overlayer and a thin substrate layer. Heat flow calculations, which model the temperature profiles during and after the laser pulse, confirm this model and also account for the highly abrupt interface between the reacted ternary overlayer and the binary substrate. The excellent agreement between experiment and theory demonstrates that thermal properties of the semiconductor have a dominant influence on the interfacial temperature profile and threshold energy density for reaction.

Notes: General computerized control and data-handling support for TFTR diagnostics is presented within the context of the Central Instrumentation, Control and Data Acquisition (CICADA) System. Procedures, hardware, the interactive man–machine interface, event-driven task scheduling, system-wide arming and data acquisition, and a hierarchical data base of raw data and results are described. Similarities in data structures involved in control, monitoring, and data acquisition afford a simplification of the system functions, based on "groups'' of devices. Emphases and optimizations appropriate for fusion diagnostic system designs are provided. An off-line data reduction computer system is under development.

Notes: The patterns of regeneration of Pteridium aquilinum (L.) Kuhn. (bracken) rhizome segments grown in pot culture are described. The overall capacity for regeneration was unaffected by the rhizome type planted, i.e., whether it consisted of only a length of frond-bearing ‘short shoote’ or whether this was attached to part of the main storage and exploratory ‘long shoot’. In all cases rhizomes extended, produced new lateral buds and developed fronds during the first summer. Regenerative capacity was also similar for segments with or without apical buds. Different patterns of growth were observed in plants grown from different types of segment: in particular, more new lateral buds were produced on rhizome segments originally lacking an apex. As rhizomes extended, the distance between successive lateral buds increased. The results are discussed in relation to the possible roles of correlative inhibition and patterns of translocation between fronds and rhizomes and to information on field populations.

Notes: The effects of growing young plants of Pteridium aquilinum (L.) Kuhn (bracken) in shaded and unshaded conditions and with differential applications of nitrogen, phosphate and balanced fertilizer are described. The results are discussed in relation to possible effects on correlative inhibition. Single applications of N and P have little effect, but addition of both together or of NPK fertilizer produces increased frond production and rhizome growth. Shaded plants produce fewer fronds and these are of greater surface area, but thinner than those of unshaded plants. It is suggested that increased frond production resulting from enhanced nitrogen supply and exposure to full light may make bracken more susceptible to herbicide applications. Etudes sur la croissance de Pteridium aquilinum (L.) Kuhn (fougère). 2. Influence de l'ombre et de l'apport d'alimentsLes conséquences pour la culture de jeunes plants de Pteridium aquilinum (L.) Kuhn (fougère) de conditions d'ombre ou de pleine lumiere avec des apports différentiels d'azote, de phosphate et de NPK sont mises en lumière. Les résultats obtenus sont considérés par rapport aux effets éventuels sur l'inhibition correlative. Des apports de N ou de P seuls ont eu peu d'influence mais les deux ensemble, de même qu'un apport NPK, ont amené la production de frondes plus nombreuses ainsi qu'une croissance plus importante des rhizomes. Les plantes cultivées à l'ombre produisent moins de frondes que celles en pleine lumiere; ces frondes ont une superficie plus étendue mais elles sont plus minces. Il se peut que la production de frondes plus nombreuses par des plantes en pleine lumière, et recevant des apports de N plus importants, rendent celles-ci plus sensibles aux applications herbicides. Untersuchungen über das Wachstum von Pteridium aquilinum (L.) Kuhn (Adlerfarn). 2. Effekt von Beschattung und NährstoffzufuhrEs wird das Wachstum junger Pflanzen von Pteridium aquilinum (L.) Kuhn (Adlerfarn) unter beschatteten und unbeschatteten Bedingungen, sowie bei differenenzierter Zufuhr von Stickstoff, Phosphor und ausgewogenen Düngergaben beschrieben. Die Ergebnisse werden unter dem Aspekt möglicher Effekte auf korrelative Hemmungen diskutiert. N und P, einzeln appliziert, haben eine geringe Wirkung; beide zusammen angewandt oder die Verabreichung eines NPK-Düngers stimulieren das Wachstum von Wedeln und Rhizomen. Schattiert wachsende Pflanzen produzieren weniger Wedel. Diese haben jedoch eine grössere Oberfläche und sind dünner als diejenigen unschattierter Pflanzen. Es wird vermutet, dass eine verstärkte Wedelproduktion, unter dem Einfluss erhöhter N-Gaben und voller Lichtexposition, Adlerfarn gegenüber Herbizidapplikationen empfindlicher mechen kann.