A strong electric field applied parallel to the superlattice axis leads to Wannier-Stark localization. There are two formally equivalent pictures for the drift velocity and the diffusion coefficient, the hopping model, which is most suitable for localized states, and the band picture, which is applicable to extended states. Complete localization of carriers is achieved by strong electric and magnetic fields. In these molecule-like systems, there is a strong interdependence between the carrier spectrum and its statistical properties, the description of which requires a new approach. The related double-time character of the transport gives rise to interesting quantum effects in the current-voltage characteristics.1 Introduction The physics of carrier transport in solids has attracted a great deal of interest since the development of microstructured devices, which rely on unique transport properties. The character of the transport mechanism depends on the character of the eigenstates. Spatially localized charge carriers, which occur in disordered solids due to deep potential fluctuations, give rise to hopping. On the contrary, extended states in crystalline solids constitute the band-transport regime. Both mechanisms are quite differently affected by inelastic scattering, e.g., on phonons. In the band-transport regime, scattering acts as the mechanism limiting the mobility of the carriers. However, carge carrier motion via hopping requires inelastic scattering. This striking discrepancy between the two regimes appears to require the development of two quite different approaches. The question can be raised: Do we really need two different approaches or can we derive a general theory that is applicable both to disordered and ordered systems? In this contribution, we show that there is one general description of transport, the formulation of which starts either from the hopping or from the band picture.Let us take a closer look at crystalline solids. Even in these ordered systems, there exist various mechanisms that lead to spatially localized carriers, such as the formation of small polarons [1] in crystals with a narrow conduction band and strong interaction with phonons, the impurity hopping conduction and weak localization [2] in doped and compensated semiconductors, and the quantumHall effect [3] in a two-dimensional electron gas subject to a quantizing magnetic field. In the present paper, we focus on the localiztion of originally extended electronic states of a crystal by a strong electric field. Within the one-band approximation, the extended eigenstates of the ordered semiconductor become localized in the direction, in which the strong electric field is applied (Wannier-Stark localization). High-electric-field effects are most pronounced in layered semiconductor structures, which consist of a periodic array of alternating materials so that a one-dimensional superlattice (SL) is formed with a SL period d much larger than the lattice constant a of the constituent materials. Due to this large SL constant, high-fi...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.