Prof Michael Johnston

Abstract:

The trapped charge density at the polymer-insulator boundary of polymer transistors was monitored by terahertz time-domain spectroscopy. Additionally, the thermal removal of trapped holes and the light-induced transmission change were studied. © 2006 Optical Society of America.

Abstract:

In this contribution a detailed characterisation of the performance of three-contact polarisation-sensitive terahertz detectors will be discussed. Furthermore the appropriate mathematical formalism required for the analysis of polarisation-resolved THz measurements will be presented. In addition, measurements of the polarisation-resolved transmission of quartz and polarisation-resolved emission of (110) ZnTe will be shown in order to illustrate the relevance of polarisation in time domain measurements. Finally perspectives on experiments that require polarisation sensitivity will be discussed.

Abstract:

Terahertz photonics is a rapidly growing field. The ultra-fast dynamics of charge carriers in semiconductors is closely linked to the performance of THz photonic devices. We study a range of ion-implanted and nano-scale semiconductors for application in novel terahertz devices.

Abstract:

We have investigated the conductivity of equilibrium and photoexcited electrons in nanoporous Indium phosphide (InP) of various porosities and of two orientations: (100) and (111). We observed an enhanced transmission through the nanoporous samples compared with bulk InP, resulting from a suppression of the conductivity by the pores. The frequency-dependent conductivity was extracted numerically from the transmission data. We examined the dynamical conductivity of photoexcited carriers using optical-pump THz-probe spectroscopy. After the rapid photoexcitation of electrons, the time-resolved conductivity was observed to decay slowly, with carrier recombination lifetimes exceeding 1ns for all (100)- and (111)-oriented samples.