/ Takashi Iizuka / Professor
/ Victor I. Ryzhii / Professor
/ Irina I. Khmyrova / Assistant
Professor
/ Leonid E. Fedichkin /
Visiting Researcher
/ Maxim V. Ryzhii / Research Associate
The research activity of the Computer Solid State Physics Laboratory is aimed at investigation of semiconductor quantum functional electronic and optoelectronic devices as a base for prospective computer hardware, intercomputer links and future communication systems. It is expected that by the end of the decade about 20 percent of the components in high performance computer systems will utilize quantum electron and photonic phenomena and this could progress further.
The efforts of the members of the laboratory are focused on
The results of the research were published in 12 refereed articles in the following journals: Semiconductor Science and Technology - 1, Journal of Applied Physics - 1, Applied Physics Letters - 1, IEEE Journal of Quantum Electronics - 1, Japanese Journal of Applied Physics - 5, IEEE Transactions on Electron Devices - 1, IEE Proceedings - Optoelectronis - 2.
The results also have been presented at the following conferences: 2nd International Conference on Low Dimensional Structures and Devices (LDSD'97, Portugal) - 1, Pacific Rim Conferense on Lasers and Electro-Optics (CLEO/Pacific Rim'97, Japan) - 1, 10th International Conference on Superlattices, Microstructures and Microdevices (ICSMM-10, USA) - 2, 8th Annual Conference on Modulated Semiconductor Structures (MSS-8, USA) - 1, 1997 Joint International Meeting (France) - 2, International Topical Meeting on Microwave Photonics (MWP'97, Germany) - 1, Second International Symposium on Silicon Heterostructures: from Physics to Devices (Italy) - 1, 27th European Solid State Device Research Conference (ESSDERC'97, Germany) - - 1, International Workshop on Nano-Physics and Electronics (Japan) - 1, International Workshop on Intersubband Transitions in Quantum Well: Physics and Devices (ITQW'97, Taiwan) - 2, 2nd International Workshop on Physics and Modeling of Devices Based on Low-Dimensional Structures (Japan) - 2, Annual Meeting of American Physical Society (USA) - 1, 2nd International Conference on Mid-Infrared Optoelectronics (MIOMD'97, Czech Republic) - 1.
Refereed Journal Papers
A novel unipolar infrared photodetector - the Darlington infrared phototransistor (DIPT) - is proposed and evaluated. The DIPT is the integration of a quantum-well infrared photodetector, utilizing the electron intersubband transitions, and a hot-electron transistor. The operation principle of the DIPT is considered. Its performance is estimated using an analytical model. It is shown that the DIPT can exhibit very large responsivity. DIPTs may be useful for new detectors of infrared radiation of wavelength longer than 2 um.
A model is presented for the performance of quantum well infrared photodetectors (QWIPs) utilizing intersubband electron transitions and tunneling injection electrons. The dark current and the responsivity are derived as functions of the QWIP parameters, including the number of the QWs, in an analytical form. Nonlinear effects in the QWIP operation at high infrared power are considered and the threshold value of power density is estimated.
The excitation of the standing plasma waves in induced-base hot-electron transistors (IBHETs) and its impact on the IBHET high-frequency operation are considered for the first time. It is shown that the plasma waves result in resonant behaviour of the IBHET performance at high-frequencies. The frequency dependent small-signal transconductance of the IBHET is calculated using an analytical model. The resonant frequencies and the sharpness of the resonant peaks are found as functions of structural parameters and bias voltage. The resonant frequencies can correspond to the terahertz range. The resonant transconductance can significantly exceed the steady-state transconductances of the IBHET.
Bistable Quantum-Well Infrared Phototransistors (BQWIPs) utilizing intersubband electron phototransitions and a resonant-tunneling injection are considered. The mechanisms of the bistability effect are discussed. An analytical model of the BQWIP operation is proposed and used to derive its characteristics. To optimize the BQWIP performance the parameters of the hysteresis loops in the BQWIP characteristic are obtained as functions of its physical parameters.
A simple analytical model of quantum-well infrared photodetectors (QWIPs) utilizing intersubband electron transitions and tunneling injection of electrons is developed. It is shown that the dark current and the responsivity as functions of the QWIP parameters, including the number of the QWs, are expressed by means of solutions of a transcendent equation. This equation is valid in a wide range of parameters and conditions where QWIPs can exhibit an effective operation. Explicit formulae for the dark current and the responsivity are obtained in some important cases. Nonlinear effects in the QWIP operation are considered and threshold values of bias voltage and intensity of infrared radiation are estimated.
We study theoretically the influence of the optical generation of electrons and holes in the base of an induced-base hot-electron transistor (IBHET) on its high-frequency operation. High electron mobility is assumed in the IBHET base, so that the standing plasma waves in the base can substantially affect the induced-base IBHET performance. It is shown that the photogeneration leads to marked transformation of the resonant peaks in the IBHET frequency-dependent transconductance. This is due to the dependence of the resonant frequencies and the electron scattering time on the concentration of the photogenerated electrons and holes. The latter results in the shift of the resonant peaks to higher frequencies and their broadening. This effect can be used for an effective optical control of IBHETs operation in the terahertz range of signal frequencies.
The conversion of images into nonuniform distribution of the output current density in a multiple quantum well structure for 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 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 quantum wells. 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.
We have theoretically studied the response of quantum well intersubband photodetectors to high-frequency modulated infrared radiation. The small-signal responsivity dependent on the modulation frequency of infrared radiation and device parameters has been derived using the proposed analytical model. It has been shown that with increasing modulation frequency the roll-off of the small-signal responsivity is associated with the electron transit and capture effects which limit the device bandwidth.
Three-terminal laser-transistors with a quantum well active region and a resonant-tunneling collector are proposed and considered. It is shown that the laser-transistor is controlled by the collector voltage due to the electron extraction via the resonant-tunneling 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 the electron injection and extraction can significantly affect the laser-transistor controllability and bistability.
An analytical model of multiple-quantum well photodetectors (QWIPs) is proposed and used to evaluate their high-frequency performance. The model accounts the electron photoexcitation from the QWs, capture into them and drift of the photoexcited electrons across the barriers. The periodicity of the QW structure is assumed. The frequency-dependent responsivity is derived as a function of the QWIP parameters. It is shown that the responsivity rolloff and 3dB 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 in them. It is predicted that the bandwidth can be expanded by using the QW structures with an effective capture of electrons in the QWs.
We have studied the transient response of AlGaAs/GaAs quantum well infrared photodetectors (QWIPs) and their high-frequency performance using a self consistent ensemble Monte Carlo particle method. It has been shown that the photocurrent caused by the electron intersubband transitions under the influence of an ultra-short pulse of infrared radiation reveals a sharp peak followed by relatively slow decay. This is associated with the electron velocity overshoot and the and the electron transit time and capture effects.
Transient behavior of bipolar transistors with a quantum-well base and a resonant-tunneling structure in the collector is studied using the ensemble Monte Carlo particle method. The switch on/off processes as a response to trigger pulses of the collector voltage and the base current are simulated. The amplitudes and duration of the pulses providing reliable switching are obtained.
An analytical model of multiple quantum well photodetectors (QWIPs) is used to calculate their frequency-dependent responsivity and bandwidth. The device model takes into account all electron processes important for the QWIP high-frequency operation. It is shown that the roll-off of the frequency-dependent responsivity and, consequently, the bandwidth are determined by the electron transit time across the inter-QW barrier, the capture probability of electrons in the QWs and the number of the latters. The bandwidth can be expanded by using the QW structures specially designed to have large electron capture probability.
The conversion of infrared images in multiple quantum well infrared photodetector (QWIP) structure into nonuniform distribution of the current driving a light-emitting diode (LED) is considered using an analytical model. The developed model of pixelless QWIP-LED imagers takes into account transport processes determining the device operation. The contrast transfer characteristic is derived as a function of the number of quantum wells and the electron capture parameter. It is shown that the quality of the up-converted images is improved with increasing number of quantum wells. The pixelless imaging devices under consideration can effectively convert long-wavelength infrared images into short-wavelength infrared or visible images.
The paper deals with a theoretical study of the high-frequency resonant effects in induced-base hot-elecron transistors (IBHETs) associated with the excitation of standing plasma waves with a linear dispersion law. Under AC voltage applied between the emitter and base contacts with a frequency close to one of resonant frequencies the plasma waves in the base channel can lead to relatively large periodic oscillations of the barrier controlling the electron injection from the IBHET emitter to collector. As a result, the IBHET transconductance at the resonant frequencies can significantly exceed its value in low frequency limit. It is shown that the transconductance reveals gigantic resonances in the terahertz range. Due to dependence of the resonant frequencies on the biasing voltages the peak positions can be voltage tunable.
The paper deals with a theoretical study of physical phenomena limiting the high-frequency performance of QWIPs. The proposed analytical device model accounts the electron photoexcitation from QWs and capture processes, tunneling of the electrons through the emitter barrier and their drift over the barriers. The QWIP responsivity is derived in explicit analytical form as a function of the modulation frequency and structure parameters.
Ultrahigh-speed effects in quantum-well infrared photodetectors utilizing intersubband electron transitions are studied theoretically. It is shown that their ultrahigh-speed operation is limited by the electron transit-time and capture effects.
Optically controlled hot-electron transistors operating in the terahertz range of signal frequencies are studied theoretically. It is shown that the photogeneration of electrons in the transistor base tunes the plasma resonances strongly affecting the frequency-dependent transconductance.
This paper is concerned with an in-depth study of the high-frequency performance of quantum well infrared photodetectors (QWIPs) with different number of quantum wells (QWs) using the developed original analytical self-consistent model. We are able to derive for the first time the expression for the small-signal frequency dependent responsivity of the QWIPs in an explicit analytical form as functions of device structural parameters including the number of the QWs, intensity of the steady-state component of the incident infrared radiation, capture parameter, and electron transit time.
This paper deals with a theoretical analysis of the electron effects in pixelless imaging devices limiting their image transformation performance. The obtained results indicate that the quality of the up-converted images is improved with increasing number of the quantum wells having a tendency to saturation. The pixelless imagers based on integrated quantum well infrared photodetectors (QWIPs) and light-emitting diodes (LEDs) can provide the up-conversion of infrared images with contrast transfer ratio close to unity.
Lateral base resistance in bipolar transistors is one of the factors substantially limiting their potentials as ultrafast devices. The implementation of the base channel with carriers (electrons or holes) induced by a dopant layer located at some distance from the channel promotes lowering of the lateral resistance of the latter. This is due to the enhancement of the electron or hole mobility associated with the exclusion of their scattering on impurities. In this paper we show that high mobility of the carriers in induced-base heterostructure bipolar transistors (IBHBTs) can account for resonant effects caused by the excitation of standing plasma waves in the base channel.
This paper deals with a theoretical consideration of the steady-state characteristics of multiple QWIPs with a tunneling emitter, taking into account random fluctuations of the dopant and carrier distributions in QWs. An analytical model of QWIPs with randomly distributed dopants is developed and used to calculate the temperature and field dependences of the dark current and the QWIP responsivity.
We present a numerical study of metal-semiconductor-metal (MSM) photodiodes based on a planar structure composed of interdigitated Schottky contacts on top of a thin GaAs absorbing layer with lateral light input. A self-consistent ensemble Monte Carlo (MC) particle method with the Fourier transform of the calculated transient photocurrent is used to obtain the frequency dependent responsivity. It is shown that the MSM photodiodes can exhibit marked responsivity in terahertz range of signal frequencies even for contact spacing about few tenth of micrometer. The results of the MC simulation are discussed invoking proposed analytical model.
The response of n-type quantum well infrared photodetectors to incident radiation arisen due to electron transtions from bound zero-dimensional impurity states to three-dimensional (unlocalized) states is derived. The obtained hydrogenic impurity photoionization cross-section in quantum well is comparable with that of states unlocalized in the quantum well plane.
The mechanism of the quanrum well infared photodetectors operation under normal incidence condition associated with electron photoionization from the donor states in quantum wells is considered. This effect can result in a marked photoionization of the electrons under the influence of radiation polarized in the quanrum well plane.
A self-consistent ensemble Monte Carlo simulation is used to study ultra-fast electron transport in quantum well infrared photodetectors (QWIPs). It is shown that transient photocurrent triggered by a short infrared radiation pulse reveals a sharp peakfollowed by a relatively slow decay. The photocurrent peak is associated with the electron velocity overshoot effect while the slow component of the photocurrent is determined by the electron transit time and capture effects.