scispace - formally typeset
Search or ask a question

Showing papers in "Journal of Nanoelectronics and Optoelectronics in 2007"


Journal ArticleDOI
TL;DR: In this paper, a review of the development of the nanoscale phonon engineering concept and possible device applications is presented, where the focus is on tuning the phonon spectrum in the acoustically mismatched nanoand heterostructures in order to change the ability of semiconductors to conduct heat or electric current.
Abstract: Phonons, i.e., quanta of lattice vibrations, manifest themselves practically in all electrical, thermal, optical, and noise phenomena in semiconductors and other material systems. Reduction of the size of electronic devices below the acoustic phonon mean free path creates a new situation for the phonons propagation and interaction. From one side, it may complicate heat removal from the downscaled devices. From the other side, it opens up an opportunity for engineering phonon spectrum in nanostructured materials, and achieving enhanced operation of nanoscale devices. This chapter reviews the development of the nanoscale phonon engineering concept and discusses possible device applications. The focus of this review is on tuning the phonon spectrum in the acoustically mismatched nanoand heterostructures in order to change the ability of semiconductors to conduct heat or electric current. New approaches for the electron–phonon scattering rates suppression and improvement of the carrier mobility as well as for formation of the phonon stop-bands are discussed. The phonon engineering concept can be potentially as powerful as the band gap engineering, which led to some ground-breaking developments in the electronics.

113 citations


Journal ArticleDOI
TL;DR: In this paper, a spectral gap-free broadband terahertz radiation (0.3 THz−30 THz) generation and detection system using amorphous electrooptic polymers is presented.
Abstract: We review recent research using organic materials for generation and detection of broadband terahertz radiation (0.3 THz−30 THz). The main focus is on amorphous electrooptic (EO) polymers, with semiconducting polymers, molecular salt EO crystals, and molecular solutions briefly discussed. The advantages of amorphous EO polymers over other materials for broadband THz generation (via optical rectification) and detection (via EO sampling) include a lack of phonon absorption (good transparency) in the THz regime, high EO coefficient and good phase-matching properties, and, of course, easy fabrication (low cost). Our ∼12-THz, spectral gap-free THz system based on a polymer emitter-sensor pair is an excellent demonstration of the advantages using of EO polymers. We also present a model that can predict the performance of a polymer-based THz system. Both the dielectric properties of an EO polymer and laser pulse related parameters are included in the model, making the simulations close to real conditions. From our modeling work, the roles the dielectric properties play in the THz generation and detection are clearly seen, providing us with a good guide to select and design suitable EO polymers in the future.

82 citations



Journal ArticleDOI
TL;DR: In this paper, planar electric metamaterials are experimentally studied in transmission and reflection utilizing terahertz time-domain spectroscopy and the authors provide an estimate of the frequency-dependent transmissivity, reflectivity, and absorptivity of metammaterial composites.
Abstract: Planar electric metamaterials are experimentally studied in transmission and reflection utilizing terahertz time-domain spectroscopy. Electrically resonant behavior is observed and provides an estimate of the frequency-dependent transmissivity, reflectivity, and absorptivity of metamaterial composites. Numerical simulations are in good agreement with the measured results and provide additional information helpful in understanding their electromagnetic response. Our results and approach help define the boundaries of a metamaterials-based design paradigm and should prove beneficial in future terahertz applications, particularly with respect to novel filtering, modulation, and switching devices. In addition, this work clarifies some of the mechanisms that limit efficient metamaterials operation at higher-frequencies.

34 citations


Journal ArticleDOI
TL;DR: In this article, a review of far-infrared properties of popular bulk and nanostructured wide-bandgap semiconductors in the broadband terahertz region is presented.
Abstract: A review of far-infrared properties of popular bulk and nanostructured wide-bandgap semiconductors in the broadband terahertz region is presented. Such wide-bandgap semiconductor materials have shown promising applications in terahertz optoelectronics. The optical, dielectric or electric properties of bulk crystalline GaN, ZnO, and ZnS, and nanostructured ZnO and ZnS were characterized by terahertz time-domain spectroscopy measurements. Theoretical fitting based on dielectric models and effective medium models have shown good agreement with the measured results. The investigation reveals that the free-standing GaN exhibits a Drude-like behavior in the terahertz region, while the dielectric response of crystalline ZnO and ZnS is dominated by low-frequency transverse optical phonon modes. The ZnO tetrapod nanostructures exhibit very similar phonon resonances with that of single-crystal ZnO, whereas the phonon confinement in ZnS nanoparticles gave rise to a difference photon response compared to the bulk ZnS.

32 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discuss the potential for creating a room-temperature tunable continuous-wave terahertz source based on nonlinear mixing within the active medium of either a dual-color high-power semiconductor laser or a laser amplifier, preferably operating at telecom wavelengths.
Abstract: We discuss the potential for creating a room-temperature tunable continuous-wave terahertz source based on nonlinear mixing within the active medium of either a dual-color high-power semiconductor laser or a laser amplifier, preferably operating at telecom wavelengths. By minimization of the terahertz waveguide losses and by enhancement of the second-order nonlinearity of the active media, our simulations indicate that one can expect the output power to reach at least 20 muW at an infrared radiation power of 100 mW per color.

15 citations





Journal ArticleDOI
TL;DR: In this paper, the authors have implemented quantum cascade lasers (QCLs) operating at about 2.5 THz in a spectrometer for high resolution molecular spectroscopy, and the absolute frequency was determined simultaneously with the absorption signal by mixing a small part of the radiation from the QCL with that from a gas laser.
Abstract: We have implemented quantum cascade lasers (QCLs) operating at about 2.5 THz in a spectrometer for high resolution molecular spectroscopy. One QCL has a Fabry-Perot resonator while the other is a distributed feedback laser. Linewidth and frequency tunability of both QCLs were investigated by mixing the radiation from the QCL with that from a 2.5 THz gas laser. Both were found sufficient for Doppler limited spectroscopy. Rotational tranistions of methanol were detected in absorption using a QCL as radiation source. Amplitude as well as frequency modulation of the output power of the QCL were used. The absolute frequency was determined simultaneously with the absorption signal by mixing a small part of the radiation from the QCL with that from a gas laser. The pressure broadening and the pressure shift of a rotational transition of methanol at 2.519 THz were measured in order to demonstrate the performance of the spectrometer.

12 citations





Journal ArticleDOI
TL;DR: In this article, the authors used ultrafast terahertz (THz) pulses for the study of low-energy excitations of photoexcited quasi 2D electron-hole (e-h) gases.
Abstract: Excitons are of fundamental interest and of importance foropto-electronic applications of bulk and nano-structured semiconductors.This paper discusses the utilization of ultrafast terahertz (THz) pulsesfor the study of characteristic low-energy excitations of photoexcitedquasi 2D electron-hole (e-h) gases. Optical-pump THz-probe spectroscopyat 250-kHz repetition rate is employed to detect characteristic THzsignatures of excitons and unbound e-h pairs in GaAs quantum wells.Exciton and free-carrier densities are extracted from the data using atwo-component model. We report the detailed THz response and pairdensities for different photoexcitation energies resonant to heavy-holeexcitons, light-hole excitons, or the continuum of unbound pairs. Suchexperiments can provide quantitative insights into wavelength, time, andtemperature dependence of the low-energy response and composition ofoptically excited e-h gases in low-dimensionalsemiconductors.



Journal ArticleDOI
TL;DR: In this paper, the authors compare and contrast gain calculations for a laser concept in deltadoped p-Ge and p-GaAs and conclude that Ge is the superior material when considering only the factor of optical gain, but the possibility of lasing in GaAs can take advantage of a wider range of growth opportunities.
Abstract: This paper reviews, compares, and contrasts recent gain calculations for a laser concept in deltadoped p-Ge and p-GaAs. Gain is calculated using distribution functions, determined from Monte Carlo simulations, for hot holes in crossed electric and magnetic fields. The results suggest that Ge is the superior material when considering only the factor of optical gain, but the possibility of lasing in GaAs can take advantage of a wider range of growth opportunities.