Ultrafast high-field transport in semiconductors

• Applicant: Professor Dr. Klaus Reimann
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2012 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 204380117

In most cases charge transport in bulk materials is governed by Ohm’s law, implying that the carrier velocity is proportional to the applied electric field. This is in contrast to Newton’s law, implying that the carrier acceleration is proportional to the field. These two models can be reconciled by scattering events occurring with a high rate. Thus, Ohm’s law cannot be valid on timescales shorter than the interval between two scattering events (about 200 fs in GaAs at room temperature). This project aims at understanding high-field charge transport in semiconductors on ultrafast time scales. Ultrashort coherent electric field transients in the THz range serve for driving carriers under extreme nonequilibrium conditions and the field emitted by the accelerated charges serves as a probe for their time-dependent motion. The main purpose of this project is the study of high-field transport of holes in elemental (silicon, germanium) and zincblende semiconductors (gallium arsenide). The transport of holes is determined by the anisotropic nonparabolic structure of the valence bands, comprising heavy-hole, light-hole, and split-off bands. In contrast to electrons, the transport of holes is influenced by scattering between these valence bands. By varying the separation between the valence bands with uniaxial stress, we will study the influence of inter-valence-band scattering on transport. Furthermore, we will investigate the transport of electrons and holes together and the field-induced tunneling between valence and conduction bands in p-type material.

• DFG Programme: Research Grants
• Major Instrumentation: Pulse shaper
• Instrumentation Group: 5770 Lichtmodulatoren, Elektrooptik, Magnetooptik