Hot Electrons In Delta-doped Gaas(si) Layers

Low temperature (2K) photoluminescence measurements have been performed in delta-doped GaAs(Si) layers, with carrier sheet concentrations Ns ranging from 1012 to 1013cm-2. Under the same excitation intensity, the luminescence spectra of all samples show a high energy tail which becomes more pronounced as Ns increases. Well defined electron temperatures, higher than the lattice temperature, are obtained, characterizing the electron heating effect in this system. The architecture of the delta-doping allows to observe hot electrons even at relatively low laser pumping intensities. © 1990.759707710Shah, Leite, (1969) Phys. Rev. Lett., 22, p. 1304Shah, (1978) Solid State Electron., 21, p. 43Meneses, Jannuzzi, Leite, (1973) Solid State Commun., 13, p. 245Shah, (1989) Superlattices and Microstructures, 6, p. 293. , See for example, and references thereinShah, Pinczuk, Gossard, Wiegmann, (1985) Phys. Rev. Lett., 54, p. 2045Kash, Shah, Block, Gossard, Wiegmann, (1985) Physica, 134 B, p. 189Yang, Carlson-Swindle, Lyon, Worlock, (1985) Phys. Rev. Lett., 55, p. 2359Tatham, Taylor, Ryan, Wang, Foxon, (1988) Solid State Electron., 31, p. 459Oberli̧, Wake, Klein, Henderson, Morkoç, Intersubband relaxation of photoexcited hot carriers in quantum wells (1988) Solid-State Electronics, 31, p. 413Leo, Rühle, Ploog, (1988) Phys. Rev. B, 38, p. 1947Ploog, Hauser, Fischer, Fundamental studies and device application of ?-doping in GaAs Layers and in AlxGa1?xAs/GaAs heterostructures (1988) Applied Physics A Solids and Surfaces, 45 A, p. 233Eisele, (1989) Superlattices and Microstructures, 6, p. 123Zrenner, Reisinger, Koch, Ploog, (1985) Proc. 17th Intern. Conf. on the Physics of Semiconductors, p. 325. , J.P. Chadi, W.A. Harrison, San Francisco, 1984, Springer, New YorkZrenner, Koch, Ploog, (1988) Surf. Sci., 196, p. 671Perry, Lee, Zhou, Worlock, Zrenner, Koch, Ploog, (1988) Surf. Sci., 196, p. 677Schwarz, Müller, Tempel, Koch, Weimann, (1989) Semicond. Sci. Technol., 4, p. 571Scolfaro, Mendonça, Meneses, Martins, Leite, (1990) Int. J. Quant. Chem., , accepted for publication i

Broadening Of The Si Doping Layer In Planar-doped Gaas In The Limit Of High Concentrations

A series of samples of GaAs planar doped with Si, grown by MBE at low substrate temperatures and with different doping concentrations, is investigated. A comparison of Shubnikov-de Haas measurements and self-consistent numerical calculations shows that a broadening of the doped region occurs in spite of the low growth temperature. The broadening occurs via segregation of the Si impurities with the growth surface when the solid solubility limit of Si in GaAs is exceeded. For the growth conditions used this limit is determined to be (2.1 ± 0.2) × 1019 cm-3. At high doping densities an intrinsic compensation mechanism becomes active, limiting the concentration of conduction electrons. © 1991.789793796Zrenner, Reisinger, Koch and K. Ploog, 17th ICPS, Koch and K. Ploog, 17th ICPS,, p. 325. , Springer, New YorkYamada, Makimoto, (1990) Appl. Phys. Lett., 57, p. 1022Santos, Sajoto, Zrenner, Shayegan, (1988) Appl. Phys. Lett., 53, p. 2504Santos, Sajoto, Lanzillotto, Zrenner, Shayegan, Migration of Si IN δ-doped GaAs and AlxGa1 − x As: Effect of substrate temperature (1990) Surface Science, 228, p. 55Zrenner, Koch, (1988) Inst. Phys. Conf. Series, 95, p. 1Gillman, Vinter, Barbier, Tardella, (1988) Appl. Phys. Lett., 52, p. 972Zrenner, Koch, Ploog, (1988) Surface Science, 196, p. 671Sasa, Muto, Kondo, Ishikawa, Hiyamizu, Si Atomic-Planar-Doping in GaAs Made by Molecular Beam Epitaxy (1985) Japanese Journal of Applied Physics, 24, p. L602Maguire, Murray, Newman, Beall, Harris, (1987) Appl. Phys. Lett., 50, p. 51

Heterogeneous contributions of change in population distribution of body mass index to change in obesity and underweight

From 1985 to 2016, the prevalence of underweight decreased, and that of obesity and severe obesity increased, in most regions, with significant variation in the magnitude of these changes across regions. We investigated how much change in mean body mass index (BMI) explains changes in the prevalence of underweight, obesity, and severe obesity in different regions using data from 2896 population-based studies with 187 million participants. Changes in the prevalence of underweight and total obesity, and to a lesser extent severe obesity, are largely driven by shifts in the distribution of BMI, with smaller contributions from changes in the shape of the distribution. In East and Southeast Asia and sub-Saharan Africa, the underweight tail of the BMI distribution was left behind as the distribution shifted. There is a need for policies that address all forms of malnutrition by making healthy foods accessible and affordable, while restricting unhealthy foods through fiscal and regulatory restrictions. © Copyright