Irina Khmyrova

Dark Current in Quantum Dot Infrared Photodetectors

We present the results of a new analytical model for the analysis of the dark current in realistic quantum dot infrared photodetectors (QDIPs). This model includes the effect of the space charge formed by electrons captured in QDs and donors, the self-consistent electric potential in the QDIP active region, the activation character of the electron capture and its limitation by the Pauli principle, the thermionic electron emission from QDs and thermionic injection of electrons from the emitter contact into the QDIP active region, and the existence of the punctures between QDs. The developed model yields the dark current as a function of the QDIP structural parameters, applied voltage, and temperature. It explains some features of the dark current characteristics observed experimentally.

Analysis of integrated quantum-well infrared photodetector and light-emitting diode for implementing pixelless imaging devices

The conversion of images into nonuniform distribution of the output current density in a multiple-quantum-well structure for an infrared pixelless imaging system is considered using an analytical device model. The nonuniform current, which reproduces the incident image, is converted back to a light-emitting diode emission image by the device considered here. The developed model takes into account transport processes responsible for the device operation. An explicit expression for the contrast transfer characteristic is derived as a function of the number of quantum wells (QWs) and the electron capture parameter. It is shown that the quality of the up-converted images (contrast and resolution) is improved with increasing number of QWs. The pixelless imaging devices under consideration can effectively convert long-wavelength infrared images into short-wavelength infrared or visible images with contrast transfer ratio close to unity.

Impact of transit-time and capture effects on high-frequency performance of multiple quantum-well infrared photodetectors

An analytical model of multiple quantum-well photodetectors (QWIPs) is proposed and used to evaluate their high-frequency performance. The model accounts for the electron photoexcitation from the QWs, capture into them and drift of the photoexcited electrons across the barriers. The frequency-dependent responsivity and the gain-bandwidth efficiency are derived as functions of the QWIP parameters. It is shown that the responsivity roll-off and 3 dB bandwidth are determined by the electron transit-time and capture effects, so that the main factors limiting the QWIP high-frequency performance are the number of the QWs and the rate of the electron capture into them. It is predicted that the gain-bandwidth efficiency weakly depends on the number of the QWs and capture parameter.

Analysis of Fringing Effect on Resonant Plasma Frequency in Plasma Wave Devices

The effect of fringing electric field due to the nonideality of the gate two-dimensional electron gas (2DEG) channel capacitance on the fundamental resonant frequency of plasma waves in a high-electron-mobility transistor (HEMT) channel was investigated. The spatial distribution of sheet electron density in the fringed region of the 2DEG channel and the expression for the fundamental resonant frequency of plasma oscillation were obtained. A cascaded transmission line (TL) equivalent circuit model was developed to represent the gated and ungated fringed regions of the HEMT 2DEG channel. Results of calculation and IsSpice simulation show that fringing effects can be the cause of the fundamental plasma frequency reduction. Thus, the developed fringing effect model improves the deviation between theoretical and experimental data.

Quantum Well Infrared Photodetector with Optical Output

A quantum well infrared photodetector which converts long-wavelength infrared radiation into short-wavelength infrared (or visible) radiation is considered. The quantum well infrared photodetector utilizes an intraband absorbtion of radiation in a quantum well in the emitter and interband emission in either classical or quantum well in the collector. It is shown that the efficiency of energy conversion of short-wavelength radiation into long-wavelength radiation can be about unity.

Photon mechanism of image smearing in integrated QWIP-LED pixelless devices

An analytical model of an integrated quantum-well infrared photodetector (QWIP) and light-emitting diode (LED) operating as a pixelless image up-converter is developed and used to estimate the device performance. It is shown that the reabsorption of the near-infrared photons trapped in the LED due to total internal reflection and their reemission can significantly influence the quality of the output image.

Characteristics of integrated QWIP-HBT-LED up-converter

In this paper, we evaluate characteristics of a novel device based on the integration of a quantum well IR photodetector (QWIP), a heterostructure bipolar transistor (HBT), and a light-emitting diode (LED) for up-conversion of middle infrared (IR) into near IR (visible) radiation. Its operation is associated with intersubband absorption of middle IR radiation in the QWIP, amplification of the QWIP output electric signal in the HBT, and emission of near IR or visible radiation from the LED fed by the current injected from the HBT. This device allows us to use Si sensors for IR and thermal imaging and significantly surpass the one based on integration of a QWIP and a LED. If the HBT current gain is high enough, the total noise of the IR camera with the up-converter can be comparable to that of the QWIP electrically connected to a read-out circuit. The major sources of the excess noise are shot noise and 1/f noise of the HBT and shot noise of the charge coupled device (CCD) sensor. The criteria to reduce their influence are established. The QWIP-HBT-LED up-converter becomes most advantageous for megapixel focal plane arrays and high read-out rate cameras.

PLASMA WAVES IN TWO-DIMENSION AL ELECTRON SYSTEMS AND THEIR APPLICATIONS

We overview the plasma properties of a two-dimensional electron gas in semiconductor heterostructures as well as new concepts and proposals of novel terahertz devices (detectors, sources utilizing plasma instabilities, and photomixers) based on these heterostructures.

High-frequency performance of lateral p-n junction photodiodes

We developed an analytical device model for quantum well lateral p-n junction photodiodes (LJPDs). The model takes into account the features of the carrier transport in LJPDs and their geometry, which ensure short transit times and a low capacitance. This model is used for calculating the LJPDs characteristics as functions of the signal frequency, bias voltage, and structural parameters and for the estimation of the LJPD ultimate performance.

Heterostructure laser-transistors controlled by resonant-tunnelling electron extraction

Three-terminal laser-transistors with a quantum well active region and a resonant-tunnelling collector are proposed and considered. It is shown that the laser-transistor is controlled by the collector voltage due to electron extraction via the resonant-tunnelling structure. The current - voltage and light - voltage characteristics are calculated. Both of them reflect effective voltage control and possible bistable behaviour of the laser-transistor in a certain range of the collector voltage. The electron heating due to electron injection and extraction can significantly affect the controllability and bistability of the laser-transistor.