Population-inversion and gain estimates for a semiconductor TASER

We have investigated a solid-state design advanced (see Soref et al, in SPIE Proceedings, vol. 3795, p, 516, 1999) to achieve a terahertz-amplification-by-the-stimulated-emision-of-radiation (TASER), The original design was based on light-to heavy-hole intersubband transitions in SiGe/Si heterostructures, This work adapts the design to electron intersubband transitions in the more readily available GaAs/Ga1-xAlxAs material system. It is found that the electric-field induced anti-crossings of the states, derived from the first excited state with the ground states of a superlattice in the Stark-ladder regime, offers the possibility of a population inversion and gain at room temperature

Responsivity of quantum well infrared photodetectors at terahertz detection wavelengths

A first-principles model of the photocurrent in quantum well infrared photodetectors (QWIPs) is derived. The model examines the responsivity, carrier capture probability and quantum efficiency. It is found that the QWIP sensitivity reaches a plateau below the 10 µm detection wavelength and remains nearly constant from 10 to 50 µm. © 2002 American Institute of Physics

Design of a tunable, room temperature, continuous-wave terahertz source and detector using silicon waveguides

We describe the design of a silicon-based source for radiation in the 0.5-14 THz regime. This new class of devices will permit continuously tunable, milliwatt scale, cw, room temperature operation, a substantial advance over currently available technologies. Our silicon terahertz generator consists of a silicon waveguide for near-infrared radiation, contained within a metal waveguide for terahertz radiation. A nonlinear polymer cladding permits two near-infrared lasers to mix, and through difference-frequency generation produces terahertz output. The small dimensions of the design greatly increase the optical fields, enhancing the nonlinear effect. The design can also be used to detect terahertz radiation

Designing strain-balanced GaN/AlGaN quantum well structures: Application to intersubband devices at 1.3 and 1.55 mu m wavelengths

A criterion for strain balancing of wurtzite group-III nitride-based multilayer heterostructures is presented. Single and double strain-balanced GaN/AlGaN quantum well structures are considered with regard to their potential application in optoelectronic devices working at communication wavelengths. The results for realizable, strain-balanced structures are presented in the form of design diagrams that give both the intersubband transition energies and the dipole matrix elements in terms of the structural parameters. The optimal parameters for structures operating at lambda ~1.3 and 1.55 µm were extracted and a basic proposal is given for a three level intersubband laser system emitting at 1.55µm and depopulating via resonant longitudinal optical(LO)phonons (h omega(LO)approximate to 90 meV). © 2003 American Institute of Physics

Mid-Infrared Silicon Photonics

A mid-infrared silicon nanophotonic integrated circuit platform can have broad impact upon environmental monitoring, personalized healthcare, and public safety applications. Development of various mid-IR components, including optical parametric amplifiers, sources, modulators, and detectors, is reviewed

Terahertz gain in a SiGe/Si quantum staircase utilizing the heavy-hole inverted effective mass

Modeling and design studies show that a strain-balanced Si1−xGex/Si superlattice onSi1−yGey-buffered Si can be engineered to give an inverted effective mass HH2 subband adjacent to HH1, thereby enabling a 77 K edge-emitting electrically pumped p–i–pquantum staircase laser for THz emission at energies below the 37 meV Ge–Ge optical phonon energy. Analysis of hole-phonon scattering, lifetimes, matrix elements, and hole populations indicates that a gain of 450 cm−1 will be feasible at f = 7.3 THz during 1.7 kA/cm2 current injection

Direction-dependent Optical Modes in Nanoscale Silicon Waveguides

On-chip photonic networks have the potential to transmit and route information more efficiently than electronic circuits. Recently, a number of silicon-based optical devices including modulators, buffers, and wavelength converts have been reported. However, a number of technical challenges need to be overcome before these devices can be combined into network-level architectures. In particular, due to the high refractive index contrast between the core and cladding of semiconductor waveguides, nanoscale defects along the waveguide often scatter light into the backward-propagating mode. These reflections could result in unwanted feedback to optical sources or crosstalk in bidirectional interconnects such as those employed in fiber-optic networks. It is often assumed that these reflected waves spatially overlap the forward-propagating waves making it difficult to implement optical circulators or isolators which separate or attenuate light based on its propagation direction. Here, we individually identify and map the near-field mode profiles of forward-propagating and reflected light in a single-mode silicon waveguide using Transmission-based near-field scanning optical microscopy (TraNSOM). We show that unlike fiber-optic waveguides, the high-index-contrast and nanoscale dimensions of semiconductor waveguides create counter propagating waves with distinct spatial near-field profiles. These near-field differences are a previously-unobserved consequence of nanoscale light confinement and could provide a basis for novel elements to filter forward-propagating from reflected light

Phonon-pumped terahertz gain in n-type GaAs/AlGaAs superlattices

Local population inversion and far-IR gain are proposed and theoretically analyzed for an unbiased n-doped GaAs/Al0.15Ga0.85As superlattice pumped solely by phonons. The lasing transition occurs at the Brillouin zone boundary of the superlattice wave vector kzbetween the two conduction minibands CB1 and CB2 of the opposite curvature in kzspace. The proposed waveguided structure is contacted above and below by heat sinks at 300 K and 77 K, respectively. Atop the superlattice, a heat buffer layer confines longitudinal optical phonons for enhanced optical-phonon pumping of CB1 electrons. A gain of 345 cm−1 at 4.5 THz is predicted for a doping density of 2.8×1016 cm−3