Abstract-Ultrafast two-dimensional field spectroscopy of terahertz intersubband saturable absorbers

Jürgen Raab, Christoph Lange, Jessica L. Boland, Ignaz Laepple, Martin Furthmeier, Enrico Dardanis, Nils Dessmann, Lianhe Li, Edmund Linfield, A. Giles Davies, Miriam S. Vitiello, and Rupert Huber

(a) Schematic diagram of the THz saturable absorber structure showing the grating and the MQW stack. 𝛿$\delta$-Si: Silicon delta-doping layers. (b) Electron envelope functions of the first (𝛹1${\Psi }_1$, red) and second (𝛹2${\Psi }_2$, blue) subbands, and the conduction band edge (CB, black), in the MQW structure. (c) Cross section of the sample, showing the simulated field enhancement of the z-component ℰ𝑧${\mathcal{E}}_z$at 2.7 THz underneath one period of the gold grating, normalized to the incident electric field. Dashed horizontal lines indicate a GaAs layer, separating the MQW section from the metal grating. Lower panel: magnified view of the marked part of the upper panel. (d) Electric field waveform of the THz pulses used to excite the ISB system. (e) Amplitude spectrum of the THz transient shown in (d) along with the measured field transmission of the sample. The blue arrow indicates the expected ISB transition frequency. (f) Experimental principle showing the two identical THz pulses with fieldsℰA${\mathcal{E}}_{\text{A}}$andℰB${\mathcal{E}}_{\text{B}}$ delayed by a time 𝜏$\tau$, which prepare and interrogate the structure’s nonlinear response.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-3-2248

Intersubband (ISB) transitions in semiconductor multi-quantum well (MQW) structures are promising candidates for the development of saturable absorbers at terahertz (THz) frequencies. Here, we exploit amplitude and phase-resolved two-dimensional (2D) THz spectroscopy on the sub-cycle time scale to observe directly the saturation dynamics and coherent control of ISB transitions in a metal-insulator MQW structure. Clear signatures of incoherent pump-probe and coherent four-wave mixing signals are recorded as a function of the peak electric field of the single-cycle THz pulses. All nonlinear signals reach a pronounced maximum for a THz electric field amplitude of 11 kV/cm and decrease for higher fields. We demonstrate that this behavior is a fingerprint of THz-driven carrier-wave Rabi flopping. A numerical solution of the Maxwell-Bloch equations reproduces our experimental findings quantitatively and traces the trajectory of the Bloch vector. This microscopic model allows us to design tailored MQW structures with optimized dynamical properties for saturable absorbers that could be used in future compact semiconductor-based single-cycle THz sources.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract-Probing the photophysics of semiconductor nanomaterials using optical pump-terahertz probe spectroscopy: from nanowires to perovskites

Hannah J. Joyce, Lissa Eyre, Stephanie O. Adeyemo, Sarwat A. Baig, Jessica L. Boland, Christopher L. Davies, Michael B. Johnston, Felix Deschler, H. Hoe Tan, C. Jagadish,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10724/107240F/Probing-the-photophysics-of-semiconductor-nanomaterials-using-optical-pump-terahertz/10.1117/12.2320720.short?SSO=1

Optical pump-terahertz probe spectroscopy is a powerful contact-free technique for probing the electronic properties of novel nanomaterials and their response to photoexcitation. This technique can measure charge carrier transport and dynamics with sub-picosecond temporal resolution. Electrical conductivity, charge carrier lifetimes, mobilities, dopant concentrations and surface recombination velocities can be measured with high accuracy and with considerably higher throughput than achievable with traditional contact-based techniques. We describe how terahertz spectroscopy is revealing the fascinating properties and guiding the development of a number of promising semiconductor materials, with particular emphasis on III-V semiconductor nanowires and devices.

© 2018 COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Abstract-Investigations of doping via optical pump terahertz-probe spectroscopy

 Jessica L. Boland,   A. Casadei,   G. Tütüncouglu,  F. Matteini , C. Davies,  F. Gaveen, F. Amaduzzi,   H.J. Joyce,  L.M. Herz,   A. Fontcuberta i Morral,  Michael B. Johnston

http://ieeexplore.ieee.org/document/8066895/

Reliable doping in semiconductor nanowires is essential for the development of novel optoelectronic devices. Dopant incorporation within the nanowire can allow for optimisation of key optoelectronic properties, such as electron mobility and carrier lifetime. Thus, in-depth characterisation of doping mechanisms in semiconductor nanowires and their effect on the nanowire optoelectronics properties is crucial. However, extraction of the dopant concentration by conventional electrical methods remains difficult due to the associated challenges with fabricating lateral contacts onto the nanowire. In this work, we present a non-contact technique based on optical pump terahertz-probe spectroscopy for examining the extrinsic carrier concentration and optoelectronic properties of semiconductor nanowires. By extracting the temperature-dependent charge carrier dynamics, we show for the first time that the dopant activation energy and underlying scattering mechanisms affecting charge carrier mobility in these nanostructures can be determined via terahertz spectroscopy.

Abstract-Broad Band Phase Sensitive Single InP Nanowire Photoconductive Terahertz Detectors

Kun Peng, Patrick Parkinson, Jessica L. Boland, Qian Gao, Yesaya C. Wenas, Christopher Davies, Ziyuan Li, Lan Fu, Michael B Johnston, Hark Hoe Tan, and Chennupati Jagadish

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/acs.nanolett.6b01528

Publication Date (Web): July 14, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.6b01528
Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful tool for materials characterization and imaging. A trend towards size reduction, higher component integration and performance improvement for advanced THz-TDS systems is of increasing interest. The use of single semiconducting nanowires for terahertz (THz) detection is a nascent field that has great potential to realize future highly-integrated THz systems. In order to develop such components, optimized material optoelectronic properties and careful device design are necessary. Here, we present antenna-optimized photoconductive detectors based on single InP nanowires with superior properties of high carrier mobility (∽1260 cm2V-1s-1) and low dark current (∼10 pA), which exhibit excellent sensitivity and broadband performance. We demonstrate that these nanowire THz detectors can provide high quality time-domain spectra for materials characterization in a THz-TDS system, a critical step towards future application in advanced THz-TDS system with high spectral and spatial resolution.