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We demonstrate that polarization-resolved THz cyclotron spectroscopy enables the transport properties of spin-split 2D heavy-holes in strained Ge quantum wells to be determined. The Rashba spin-orbit interaction strength is found from the magnetic-field dependence of the cyclotron frequencies. In high-mobility samples the optical quantum Hall effect is witnessed, where the transverse magnetoconductivity...
We report the observation of multiple polariton branches in an ultra-strongly coupled system of Landau level transitions in strained Ge quantum wells (sGe QWs) and a THz metamaterial. The sGe QW system shows narrow spin-split heavy-hole cyclotron resonances and thus leads to multiple cyclotrons. The coupled system can be described by an expanded ultra-strong coupling Hamiltonian including all oscillators...
Coherent zone folded acoustic phonons in terahertz quantum cascade laser (QCL) structures [1] are investigated by high-speed asynchronous optical sampling [2]. This method is based on two Ti:sapphire lasers with repetition rates of ∼1 GHz respectively. The time delay between pump and probe pulse is achieved by an offset in repetition rate of 5kHz. This allows for fast scanning times without moving...
We have improved the stability and performance of terahertz photoconductive (Auston) switches using a combination of (NH4)2S surface passivation and silicon nitride (Si3N4) encapsulation. The passivation and encapsulation processes increased the average terahertz power generated four-fold.
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.
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.
We report the complex refractive index of La5/3Sr1/3NiO4 over the terahertz frequency range, obtained using time-domain spectroscopy. Negligible change in the complex refractive index with magnetic flux densities up to 6 T was seen, while changes were observed as the lattice temperature was increased from 1.5 K to the charge-ordering temperature at 220 K. The terahertz frequency response therefore...
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...
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...
Ultrafast charge carrier dynamics in semiconducting materials ultimately determine the performance of photoconductive terahertz (THz) emitters and receivers. Ion implantation of III-V semiconductors allows carrier dynamics to be tailored for a particular application, and thus the technique is increasingly being applied to the development of advanced materials for terahertz photonics. In this talk...
We have used differential terahertz spectroscopy to monitor performance degradation in state-of-the-art polymer field effect transistors (pFETs) based on poly[(9,9-dioctylfluorene-2,7-diyl)-co-(bithiophene)] (F8T2). After extended periods of operation holes are trapped in the polymer, increasing the device's threshold voltage. We monitor the trapped charge density using THz spectroscopy, and investigate...
Research on polymer-based transistors is leading to the development of flexible, printable circuitry, which were extremely cost effective to manufacture. However, the long-term performance of state-of-the-art polymer field effect transistors (pFETs) is limited by device degradation. We show that terahertz spectroscopy is an ideal tool to probe polymer device performance. Specifically we have monitored...
The spectral width of terahertz emission from ion-implanted terahertz emitters increases with ion damage, owing to ultrafast carrier capture. Carrier dynamics simulations reinforce these findings. Optical-pump, terahertz-probe experiments confirm the sub-picosecond lifetimes of these materials.
We present a terahertz radiation detector that measures both transverse components of a terahertz single cyclepsilas electric field, allowing the study of polarization dependent properties of materials. Measurements of birefringence in quartz are presented.
We simulate the terahertz emission from laterally biased InGaAs and InP using a three-dimensional carrier dynamics model in order to optimise the semiconductor material. Incident pump-pulse parameters of current Ti:Sapphire and Er:fibre lasers are chosen, and the simulation models the semiconductor's bandstructure using parabolic Γ, L and X valleys, and heavy holes. The emitted terahertz radiation...
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