The main aim of this paper is to analyze the propagation and attenuation in PIR fibers. The thermal change of these
parameters for different mode structures will be done due to propagation of high optical power witch cases fiber
We study theoretically a heterostructure device with the structure akin to a high-electron mobility transistor which can be
used to generate electro-magnetic radiation in the terahertz range of frequencies. The gated electron channel is supplied
with a lateral Schottky contact serving as the source. The operation of the device is associated with photomixing of
optical signals in high-electric-field depletion region of the Schottky junction. The electrons and holes photogenerated in
the Schottky junction depletion region and propagating across it induce the ac current in the quasi-neutral electron channel
which, in turn, excites the plasma oscillations in this channel. Fast electron transport in the Schottky junction depletion
region and resonant properties of the electron channel provide an enhanced response of the photomixer to optical signals
at the plasma frequencies.
We develop device models of a terahertz (THz) photomixer based on
a high-electron mobility transistor (HEMT) structure utilizing
the excitation of electron plasma oscillations in the HEMT channel by the electrons and holes photogenerated by optical signals.
We use hydrodynamic equations both for electrons in the channel and
for photoelectrons and photoholes in the absorption layer, or hydrodynamic equations for electrons in the channel combined with
a kinetic description of the photogenerated carriers, and the Poisson equation for the self-consistent electric field. The models are used for an analytical as well as numerical (based on an ensemble Monte Carlo particle technique) analysis of the HEMT-photomixer operation in the THz frequency range.
We review recent studies of physical phenomena in quantum well infrared photodetectors (QWIPs), and some other QW and QD infrared devices and discuss their features. We show that the optimization of QWIPs, improvement of QDIPs, and creation of novel QWIP- and QDIP-based devices still requires an in-depth understanding of underlying physical effects.
This paper deals with a physical analysis of the factors determining the operation of the quantum dot and quantum wire infrared photodetectors and their features focusing on semi-qualitative approach and comparison with quantum well infrared photodetectors. We address also the problems of computer modeling of these photodetectors.
We present a device model for a lateral p-n junction quantum-well edge-emitting laser-transistor with an extra gate contact. Such a contact provides an opportunity to control the confinement conditions of the electrons injected into the active region and, as a consequence, the threshold current and output optical power by the
gate voltage. Using the proposed model, we calculate the laser dc characteristics and estimate its modulation performance. We show that the application of negative gate voltages can lead to a substantial decrease in the threshold current. The estimated cutoff modulation frequency associated with the gate recharging can be much higher than those associated with the photon and electron lifetimes.
Mixing of two optical beams with close frequencies in photoconductive structures or their response to ultrashort optical pulses are widely used for the generation of terahertz (THz) electromagnetic radiation.
The THz radiation produced by optically excited plasma oscillations
in p-i-n structures has been observed by some teams. In this communication, we consider a heterostructure akin to a field-effect transistor with high electron mobility in its two-dimensional channel and report on the modeling of THz oscillations caused by optical signals in this heterostructure. The features of such a heterostructure are associated with the existence of weakly damped electron plasma oscillations and possibility of their resonant excitation, so that the two-dimensional electron channel serves as
a resonant cavity with rather high quality factor. A conception of THz photomixing using the excitation of standing plasma waves (plasma oscillations) in the heterostructure under consideration has recently been proposed by the authors. We demostrate that due to the excitation of the electron plasma oscillations in the channel by the photogenerated electrons and holes, the heterostructure in question
exhibits a pronounced resonant response leading to high amplitudes
of the ac photocurrent oscillations. As shown, this can result in substantially higher efficiency of the THz radiation generation by optical signals than that in p-i-n structures.
As predicted theoretically, quantum dot infrared photodetectors (QDIPs) can substantially surpass quantum well infrared photodetectors (QWIPs). Recently, a number of research groups reported fabrication and extensive experimental investigation of various InAs/GaAs, InGaAs/GaAs, and InGaAs/InGaP QDIPs. However, most of the fabricated QDIPs have worse performance than QWIPs. To answer the questions why QDIPs are still inferior to QWIPs and how to improve them, we analyze the QDIP operation using the developed device model of QDIPs with realistic parameters. The model takes into account the main physical factors determining the operation of QDIPs. We calculate the dark current and the responsivity of QDIPs as functions of their structural parameters, the applied voltage, and temperature. The calculated characteristics are in agreement with those of realistic QDIPs studied experimentally. The revealed relations between the QDIP operation characteristics and structural parameters explain the main features of QDIPs observed in experiments. We estimate the QDIP detectivity and find the conditions for its maximum value. We compare the QDIP characteristics with those of QWIPs.
This paper presents the recent developments of device models for quantum dot IR photodetectors (QDIPs) and for imagers based on the integration of these photodetectors with light emitting diodes (LEDs). We derive analytical formulas for the dark current and the responsivity in QDIPs based on different QD structures and the QDIP-LED contrast transfer characteristic as functions of the structural parameters and the bias voltage. It is shown that the characteristics of QDIPs are strongly affected by the effect of electron accumulation in QDs close to the emitter contact. The main effect limiting QDIP-LED imager resolution is associated with the processes of photon reabsorption and reemission in the device LED part.
In this paper a two-dimensional ensemble Monte Carlo particle method is used to simulate the metal-semiconductor-metal (MSM) photodetector response in the terahertz range of signal frequencies. We consider planar MSM photodetectors consisting of a GaAs absorbing layer with a system of Schottky contacts made 'back-to-back' on the above layer. The model takes into account the features of the carrier energy spectra, mechanisms of their scattering and a self-consistent electric field. The intrinsic transient response triggered by an ultra-short light pulse is calculated. The MSM frequency response is calculated using the Fourier transform of the obtained temporal dependences. It is shown that due to velocity overshoot effect exhibited by the photoelectrons, the MSM photodetector reveals rather high response to terahertz signals even if the contact spacing is relatively large. The frequency response of the MSM photodetectors utilizing the photoelectron velocity overshoot effect is compared with that of the MSM photodetectors with ultra-short carrier lifetime.