Terahertz photonics

Abstract:

The anisotropic complex dielectric properties of materials in the terahertz band is a topic that has attracted considerable attention recently in the fields of physics, chemistry and biochemistry. The mathematical formalism for analysing polarization-resolved terahertz time-domain data is presented, and particular cases including birefringence, optical activity and circular dichroism are discussed. © 2009 IOP Publishing Ltd.

Abstract:

We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.

Abstract:

Using terahertz time-domain spectroscopy we investigate how quantum, magnetic and electrostatic confinement alters the photoconductivity of nanostructured semiconductors. In 2.0 THz and 2.9THz GaAs/AlGaAs quantum cascade structures under a magnetic field we observe transitions from the 1s to 2p- or 2p+ magneto-exciton states. The electron cyclotron resonance is prominent at high excitation fluence. Additionally, we report that the conductivity of photoexcited electrons in nanoporous InP honeycombs obeys the Drude model of free-carrier absorption, while the dark conductivity does not. This finding can be explained as a result of surface band bending spatially separating photoexcited electrons and holes, and also accounts for the long electron recombination lifetime (exceeding 100 ns) at low temperature. © 2009 SPIE.

Abstract:

We report on extrinsic and photoexcited carrier behaviour in porous InP of various porosities and two orientations, studied using terahertz spectroscopy. We observed behaviour indicative of a surface electron depletion layer resulting from bandbending. ©2008 IEEE.

Abstract:

We have investigated the terahertz conductivity of extrinsic and photoexcited electrons in nanoporous indium phosphide (InP) at different pore densities and orientations. The form of electronic transport in the film was found to differ significantly from that for bulk InP. While photo-generated electrons showed Drude-like transport, the behaviour for extrinsic electrons deviated significantly from the Drude model. Time-resolved photoconductivity measurements found that carrier recombination was slow, with lifetimes exceeding 1 ns for all porosities and orientations. When considered together, these findings suggest that the surfaces created by the nanopores strongly alter the dynamics of both extrinsic and photoexcited electrons.