1,721,394 research outputs found
Recensione a: La bellezza dell'invisibile. Creatività e immaginazione nella Fisica / Giovanni Vignale, Zanichelli, 2013
No full text"La bellezza dell’invisibile: creatività e immaginazione nella fisica" è un bel volume della collezione “Saggi” di Zanichelli, traduzione dell’omonimo libro scritto da Giovanni Vignale nel 2011
Valley splitting and optical intersubband transitions at parallel and normal incidence in [001]-Ge/SiGe quantum wells
No full textWe investigate intervalley splitting in the conduction band of strained [001]-Ge quantum well (QW) systems with finite SiGe alloy barriers by means of a sp3d5s∗ tight-binding Hamiltonian. We find that interaction between germanium bulk L minima splits each confined subband into a doublet. We first characterize this splitting as a function of the well width and of the strength of a uniform electric field superimposed along the growth direction. Varying the well width, an oscillating behavior of the splitting magnitude similar to that predicted for Si QW systems is observed and explained. Then we focus on the optical intersubband transitions occurring between states belonging to the fundamental and the first-excited doublets. Selection rules for intersubband transitions at normal and parallel incidence are discussed exploiting the parity character of the involved doublet states. Numerical results for infrared-absorption spectra, evaluated for both symmetric and biased Ge QWs, support our findings
Il modello di Mossotti per la stabilità della materia", in La situazione delle Scienze al tempo della Prima Riunione degli Scienziati Italiani - 1839
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Conduction intersubband transitions at normal incidence in Si1-xGex quantum well devices
No full textWe show theoretically that it is possible to design SiGe-based quantum well structures in which conduction intersubband transitions are induced by normal incidence infrared radiation. A sp3d5s* tight binding model has been adopted to evaluate the electronic states and optical transitions between lowest conduction confined states of a superlattice composed of one pure Ge quantum well separated by SiGe alloys, grown along the [001] direction. We find that significant optical coupling between confined states in the Ge wells is achieved at normal incidence radiation by the off-diagonal elements of the mass tensor. The minimum energy Ge conduction valleys are, in fact, tilted with respect to the [001] growth axis. For comparison we show that no such coupling can be realized for the conduction states confined in a similar structure composed by Si quantum wells because the ellipsoids of the lowest conduction valleys are oriented along the growth direction
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