Long intersubband relaxation times in n-type germanium quantum wells

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Effective Selection of Quality Literature During a Systematic Literature Review

Aim/Purpose: Although a literature review is the fundamental base for any research, it is often considered tedious and conducted with a lack of methodology and rigor. The paper presents a method for systematically searching and screening literature using modern search technologies. The method focuses on minimizing the amount of manual screening by employing the references among papers. Findings: The selection method was applied to the field of literature review itself and to the field of functional modelling. In both cases, relevant literature was identified within a surprisingly short time

Pump-probe spectroscopy of interminiband relaxation and electron cooling in doped superlattices

The picosecond dynamics of electrons in a doped GaAs/AlGaAs superlattice have been investigated by pump-probe experiments using an infrared free-electron laser. We observe a fast bleaching of the interminiband absorption followed by thermalization and a slower cooling component. The latter can lead to a positive or negative transmission change, resulting from the temperature dependence of the linear absorption spectrum at the respective wavelength. We show that the superlattice in contrast to quantum wells provides a unique picosecond thermometer for the electron temperature based on the dependence of the absorption on the electron distribution function

Terahertz Ionization of Highly Charged Quantum Posts in a Perforated Electron Gas

“Quantum posts” are roughly cylindrical semiconductor nanostructures that are embedded in an energetically shallower “matrix” quantum well of comparable thickness. We report measurements of voltage-controlled charging and terahertz absorption of 30 nm thick InGaAs quantum wells and posts. Under flat-band (zero-electric field) conditions, the quantum posts each contain approximately six electrons, and an additional ∼2.4 × 10¹¹ cm⁻² electrons populate the quantum well matrix. In this regime, absorption spectra show peaks at 3.5 and 4.8 THz (14 and 19 meV) whose relative amplitude depends strongly on temperature. These peaks are assigned to intersubband transitions of electrons in the quantum well matrix. A third, broader feature has a temperature-independent amplitude and is assigned to an absorption involving quantum posts. Eight-band <i>k·p</i> calculations incorporating the effects of strain and Coulomb repulsion predict that the electrons in the posts strongly repel the electrons in the quantum well matrix, “perforating” the electron gas. The strongest calculated transition, which has a frequency close to the center of the quantum post related absorption at 5 THz (20 meV), is an ionizing transition from a filled state to a quasi-bound state that can easily scatter to empty states in the quantum well matrix

Stadtentwicklung

Die Produktpolitik des Stadtmarketings hängt auch von den Zielen, Prozessen und Ergebnissen der Stadtentwicklung ab. Die Veränderungen im Umfeld von Kommunen machen die gezielte Weiterentwicklung von Städten in vielen Feldern wie Wohnen, Demografie, Mobilität und Energie erforderlich. Damit dieser Prozess wirksam werden kann, müssen die zentralen Anspruchsgruppen und Gremien mit einbezogen werden. In diesem Unterkapitel werden einige zentrale Inhalte aufgelistet, die die Interdependenz der unterschiedlichen Entwicklungsfelder verdeutlichen. Es gibt dabei expansiv-offensive oder auch regressiv-defensive Entwicklungssituationen, die beide einer gezielten, kohärenten Steuerung bedürfen