Probing terahertz electron dynamics in semiconductor nanostructures with the UC Santa Barbara FELs (original) (raw)
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Terahertz-induced interband tunneling of electrons in GaAs
Physical Review B, 2010
Ultrafast high-field transport is studied in n-type GaAs with ultrashort terahertz ͑THz͒ pulses of an electric field amplitude of up to 300 kV/cm. At lattice temperatures between T = 300 and 80 K, we observe coherent ballistic transport of electrons over a major part of the first Brillouin zone. At T = 300 K, ballistic transport occurs at a constant electron density whereas at lower temperatures, the THz pulses generate additional electron-hole pairs by field-induced tunneling between valence and conduction bands. We show that the ultrashort decoherence time of superpositions of valence-and conduction-band states plays a crucial role for the efficiency of the tunneling process. The extremely fast interband decoherence at room temperature results in a negligible tunneling rate.
Semiconductor investigation by terahertz radiation pulses
Terahertz Emitters, Receivers, and Applications III, 2012
Several applications of terahertz radiation pulses for characterizing semiconductor bulk materials and structures are described. Terahertz pulses emitted at the surfaces illuminated by femtosecond laser of a tunable wavelength are demonstrated to provide information on the electron energy spectrum in the conduction band as well as on the subsurface band bending. On the other hand, by sampling the conductivity of various structures with short electrical field transient photoexcited electron dynamics can be directly studied at its initial, subpicosecond time scale. Narrow gap semiconductors InSb and InAs as well as novel materials such as GaAsBi or self-assembled InAs quantum dots were characterized by using terahertz radiation pulses. Downloaded From: http://www.spiedl.org/ on 10/23/2012 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8496 84960V-2 Downloaded From: http://www.spiedl.org/ on 10/23/2012 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8496 84960V-8 Downloaded From: http://www.spiedl.org/ on 10/23/2012 Terms of Use: http://spiedl.org/terms
Transition from classical to quantum response in semiconductor superlattices at THz frequencies
Physical Review B, 1996
The response of a sequential resonant tunneling superlattice to intense THz radiation shows a transition from classical rectification at frequencies below 600 GHz to quantum response above 1 THz. In the quantum regime, the dc current-voltage characteristics show distinct peaks due to absorption and stimulated emission of up to three THz photons. For sufficiently high ac field strengths the photon-assisted channels dominate the transport, leading to absolute negative conductance near zero bias, and gain just below the Stark splitting of the ground states in adjacent quantum wells. Quantitative agreement with these observations is obtained by invoking photon-assisted tunneling following Tucker, but with an instantaneous I-V free of domain formation.
Pramana, 2006
By suitable design it is possible to achieve quasi-ballistic transport in semiconductor nanostructures over times up to the ps-range. Monte-Carlo simulations reveal that under these conditions phase-coherent real-space oscillations of an electron ensemble, generated by fs-pulses become possible in wide potential wells. Using a two-color pump-and-probe technique we have been able to observe this new phenomenon in excellent agreement with
Few-cycle THz spectroscopy of nanostructures
Physica E: Low-dimensional Systems and Nanostructures, 2000
Optically excited plasma oscillations in n-doped GaAs epilayers emit intense THz pulses. Using a THz-pump and THz-probe technique we observe the response of the intersubband polarization in semiconductor quantum structures. THz Cross-correlation measurements of modulation doped semiconductor quantum structures allow to determine the absorption, the dispersion, and the dephasing times of the quantized electrons. ?
Ultrafast semiconductor spectroscopy using terahertz electromagnetic pulses
Science and Technology of Advanced Materials, 2005
Terahertz electromagnetic pulses can serve as a new and unique tool for various types of spectroscopy. We first characterized the temporal and spatial properties of THz pulses generated from a large-aperture photoconductive antena, and then used them for the study of the ultrafast dynamics of electrons in semiconductros. We studied the dynamics of electrons generated by femtosecond optical pulses with positive and negative excess energies in GaAs and InP by observing the waveform of the emitted THz radiation. Subpicosecond intraband relaxation was observed with positive excess energies. With negative excess energies, a picosecond transition from the Urbach state to free carrier states was observed.
Few-cycle THZ spectroscopy of semiconductor quantum structures
Physica E: Low-dimensional Systems and Nanostructures, 2001
Optically excited plasma oscillations in n-doped GaAs epilayers emit intense THz pulses. From THz emission experiments in doped superlattices the miniband properties can be revealed. Using a THz-pump and THz-probe technique we observe the response of the intersubband polarization in semiconductor quantum structures. THz cross-correlation measurements of modulation doped semiconductor quantum structures allow to determine the absorption, the dispersion, and the dephasing times of the quantized electrons. ?
Ultrafast Electron Dynamics in GaAs and InP Studied by Time-Resolved Terahertz Emission Spectroscopy
Japanese Journal of Applied Physics, 2004
We studied the ultrafast dynamics of electrons generated by tunable femtosecond optical pulses having positive and negative excess energies in GaAs and InP by observing the temporal waveform of THz radiation emitted from biased photoconductive antennas. Sub-picosecond intraband relaxation was observed when the excess energy was positive. When excited by optical pulses having negative excess energies, it was observed that the THz waveform had a picosecond decay, which was attributed to the transition from the Urbach state to the free carrier state of electrons on the picosecond time scale. This dynamical behavior was found to be very sensitive to the applied electric field in the range of several kV/cm. The largest THz signal was obtained by pumping the emitter at the band-gap energy.
Optical generation of terahertz pulses in quantum wells
1993
This volume is comprised of papers that were presented at the Fifth Topical Meeting on Ultrafast Electronics and Optoelectronics (formerly Picosecond Electronics and Optoelectronics), held in San Francisco, January 23-25, 1993. The purpose of this topical meeting, since its inception in 1985, has been to foster greater interaction between researchers in the electronics and optoelectronics communities who share a common interest in the physics and technology of ultrafast electronics and optoelectronics devices, their multigigahertz applications, and ultrafast measurement techniques. The number of abstracts submitted to this meeting was considerably larger than for the previous meetings, indicating the appeal of this interdisciplinary approach and the growing importance of this field. This preface serves as a summary and a guide to these Proceedings. Ultrafast Optoelectronic Devices is concerned with high speed electronic devices and presents a discussion of the state-of-the-art devices such as resonant tunneling transistors, bipolar transistors and high electron-mobility transistors, and >100 GHz Si MOSFETs. High Speed Electronic Devices discusses state-of-the-art optoelectronic devices such as lasers and detectors. Gain dynamics and carrier transport in semiconductor lasers, mode-locking of lasers, integrated laser-modulators, vertical cavity lasers, metal-semiconductor-metal photodetectors, HBT photodetectors, and photovoltaic photodetectors are some of the topics discussed in this section. Terahertz Transients is concerned with the physics and technology of generation and detection of terahertz transients from semiconductors, and applications of terahertz transients generated by high power femtosecond lasers. Physics of Semiconductors covers physics of semiconductors. This part includes a discussion of photonic bandgap, high field transport, Bloch oscillations, and coherent effects in semiconductor nanostructures. Novel Sources and Techniques covers a discussion of novel sources, such as mode-locked diode-pumped solid-state lasers, as well as novel techniques such as high spatial and temporal resolution probes using scanning force microscopes, and time-reversal using a temporal imaging system. (Sub)Millimeter Wave Devices covers generation, and control of millimeterand submillimeter-wave radiation from solid state sources using picosecond lasers, and applications of such sources for circuit characterization. Photoconductive and Electro-Optic Sampling covers recent advances in the field of photoconductive and electro-optic sampling techniques and materials; Transmission Lines covers recent advances in generation and propagation of sub-picosecond pulses using transmission lines; and xii1 Ultrafast Probes of Materials/Devices/Circuits covers recent advances in ultrafast probes of materials, devices, and circuits. The final section, Superconductors, covers the interaction of ultrashort pulses with superconductors, and its application in the optical control of an electrical circuit.