Physics and Applications of Dilute Nitrides. An Atomistic View of the Electronic Structure of Mixed Anion III–V Nitrides. Band Anticrossing in III-N-V Alloys. Tight-Binding and k·p Theory of Dilute Nitride Alloys. Electronic Properties of (Ga,In)(N,As)-Based Heterostructures. Theory of Defects in Dilute Nitrides. Growth, Characterization, and Band-Gap Engineering of Dilute Nitrides. GaInNAs Long-Wavelength Lasers.
From mobile telecommunications to crime prevention, modern technologies use a wide electromagnetic frequency spectrum. However, for the frequency range 0.3-10 terahertz (THz), referred to as the THz gap, there remains an urgent need for convenient compact solid state devices that emit/detect THz radiation in a selective and tuneable way. Such devices are relevant for many emerging applications, such as THz imaging in biomedicine, and for fundamental studies of excitations in several material systems, such as semiconductors, gaseous plasmas and proteins. The THz gap lies above the frequency range of conventional electronics (transistors) and below the frequency range of traditional optical sources (lasers). To fill this gap, we propose a novel approach to the generation/detection of THz radiation, which exploits the unique electron dynamics occurring in the semiconductor dilute nitride Ga(AsN) alloy. A small concentration of nitrogen (N) atoms has a remarkable effect on the electronic properties of GaAs. The admixing of the N-impurity levels with the extended conduction band states of GaAs leads to the formation of a fully developed energy gap in the conduction band and to subbands with highly non-parabolic energy-wavevector å(k) dispersions. Of particular interest is the form of the lower energy subband in which an inflection point, k*, occurs in the å(k) curve at wavevectors much smaller than the size of the Brillouin zone of GaAs. The electron group velocity in this subband has a maximum at k* and falls off rapidly at higher k-values, Figure a. At large electric fields, electrons can gain sufficient energy to approach k* and the energy level of the N-atoms, at which they become spatially localised, thus causing a negative differential velocity (NDV) effect in which the current flow through the device decreases with increasing applied voltage, Figure b [5-6]. This is an entirely new physical concept of great technological potential. We discovered a strong dependence of the NDV on magnetic field (Figure b), which reveals that the acceleration of electrons towards the Nlevel is a fast (<10-12 s) process of relevance for THz electronics [5]. This is confirmed by model calculations of electron transport, which indicate that the NDV can lead to harmonic generation of ac current and detection/stimulated emission of THz radiation. More importantly, the maximum response frequency associated with the NDV can be tuned by the applied electric field into the THz frequency range of interest for tuneable sources of THz radiation [7]. The development and investigation of this unusual NDV effect in Ga(AsN) will enhance not only our understanding of the fundamental electronic properties of this novel alloy, but also lead to new discoveries in a much wider variety of dilute nitride semiconductors, such as In(PN), In(SbN), In(AsN) …. Novel regimes of electron dynamics could be revealed in these material systems with exciting prospects for applications in innovative technologies.
ALONZO DAVID LINARES MORA COMUNICACIONES DE RADIO FRECUENCIA FUENTE DE ORIGEN:
No hay comentarios:
Publicar un comentario