/ Takashi Iizuka / Professor
/ Victor I. Ryzhii / Professor
/ Irina I. Khmyrova / Assistant Professor
/ G. Y. Khrenov / Assistant Professor
/ Maxim Yu. Ershov / Research Associate
/ 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 research results have been published in 12 refereed articles in the following journals: Semiconductor Science and Technology - 4, Journal of Applied Physics - 1, Applied Physics Letters - 1, COMPEL - 1, IEEE Transactions on Electron Devices - 1, Journal of Physics D: Applied Physics - 1, Physica B - 1, Japanese Journal of Applied Physics - 1, Journal de Physique III - 1.
The results also have been presented at the following conferences:
Refereed Journal Papers
In this paper we present the physical effects in quantum well infrared photodetectors (QWIPs) utilizing intersubband electron transitions. We show, using numerical modeling, that the operation of QWIP is associated with the nonuniform distribution of the electric field and other physical quantities due to the recharging of the QWs near the emitter contact. The high electric field in the emitter barrier which provides tunneling electron injection is controlled by applied voltage and infrared radiation. The transient photoelectric effects in QWIPs are determined by three time constants - electron capture time to the QWs, transit time through the QWIP structure, and recharging time of the QWs. The transient photocurrent in QWIPs with high photocurrent gain is composed of two components. The fast transient is limited by the carrier transit time, and the slow transient, exhibiting the multiplication of photocurrent, is governed by the QW recharging time. This ! study shows that contact and dstributed effects play an important role in determining both thesteady-state and transient QWIP characteristics.
The effect of the nonuniformity of the dopant density in the quantum well of an intersubband single quantum-well infrared phototransistor (QWIPT) with triangular emitter and collector barriers is studied theoretically. It is shown that the nonuniformity of the dopant distribution in the plane of the QW, in particular, its random fluctuations, can significantly increase the dark current. However, the nonuniformity does not affect the photocurrent.
A monolithic wavelength converter of long-wavelength infrared radiation to short wavelength infrared or visible radiation based on a quantum-well structure has been proposed and considered theoretically. The quantum-well converter utilizes intersubband electron transitions in the emitter quantum well. The threshold intensity of long-wavelength infrared radiation necessary for the laser generation is evaluated as a function of the device structural and physical parameters.
Infrared phototransistors based respectively on a quantum-well and a quantum-wire structures, utilizing intersubband electron transitions, are considered using developed analytical model. The dark currents and responsivities of the phototransistors in question are compared. It is shown that the quantum-wire infrared phototransistor can surpass the infrared phototransistor with a quantum well in performance especially at low temperatures. This is due to the one-dimensional nature of the electrons in the quantum-wires providing higher energy of thermal excitation, leading to low dark current and sensitivity to normal incident radiation.
A novel infrared photodetector -- the quantum-dot infrared phototransistor -- based on a multiple quantum dot structure is considered theoretically. An analytical model of the device is developed to evaluate its performance. The dark current and sensitivity are calculated. It is shown that the quantum-dot infrared phototransistor performance can surpass that of the quantum-well photodetectors.
The electrical and optical properties of quantum-well infrared phototransistors (QWIPTs) utilizing intersubband electron transitions from a single quantum well (QW) are studied theoretically. The dependences of the electron concentration in the QW, the dark current, the photocurrent and the responsivity on applied bias voltage are evaluated. The results obtained can be used for the optimization of the QWIPT performance.
Effect of the modulation of the electron density in the quantum well (QW) of intersubband single quantum-well infrared phototransistor (QWIPT) on its performance is considered theoretically. We show that the sheet electron concentration can significantly differ from the sheet concentration of the donors in the QW. The sheet electron concentration can increase with applied bias, which leads to an increase of the dark current, photocurrent, responsivity and detectivity of the QWIPT. The effect of the electron tunneling from the QW is also discussed.
We propose a simple distributed model for intersubband quantum well infrared photodetectors IQWIPs), which explicitly takes into account the injecting properties of the contacts. We show that the QWIP operation with multiple QWs involves the formation of a high-field domain near the emitter, caused by the modulation of the bound electron density in the QWs by applied voltage and infrared radiation. The external characteristics of the QWIP (total current, differential resistance, and quasistatic capacitance) are strong functions of the voltage and radiation intensity.
We study a small-signal performance of a quantum well (QW) diode with triangular emitter and collector barriers providing thermionic electron transport. Analytical expression for the QW doide admittance is obtained from the rigorous self-cinsistent small-signal analysis. Frequency dependence of the admittance is determined by a characteristic time of recharging of the QW, which is a stromg function of temperature and parameters of the QW diode. Conductance as a function of temperature shows a local maximum corresponding to a resonance between a probe signal and recharging processes. Capacitance of the QW diode depends critically on the efficiency of the electron transport through the QW, and can significantly exceed all geometric capacitances associated with the device structure. Experimental data on conductance and capacitance of the QW diode as functions of temperature and frequency can be used to extract the parameters of the QW, such as QW recombinati! on velocity, ionization energy, etc. Analytical analysis of transient currents in the QW diode allows a transparent explanation why an incremental charge-partitioning technique fails to calculate the capacitance even in the low-frequency limit.
The capacitance-voltage characteristics (C-V) of multiple-quantum-well (MQW) semiconductor heterostructures are studied using a proposed numerical model. The MQW structures with a schottky emitter contact exhibit stepwise C-V characteristics, with constant jumping of the inverse capacitance and with the distance between steps increasing with applied bias. The structures with a tunneling emitter barrier show a strong variation of capacitance, starting from large values, corresponding to the emitter barrier width at low bias, and saturating at low values, corresponding to the length of the MQW structure at high bias. These features of the C-V characteristics are associated with the re-charging of the quantum wells with applied voltage. In turn, the re-charging effects are closely related to the electron injection and transport propertryies of the MQW structures.
A novel device - the quantum-dot infrared phototransistor (QDIP) - is proposed and considered theoretically. The QDIP utilizes intersubband electron transitions from the bound states. The dark current and sensitivity are calculated using a proposed analytical model of the QDIP. It is shown that the QDIP can exhibit low dark current, high photoelectric gain and sensitivity surpassing the characteristics of other intersubband photodetectors.
An integrated wavelength converter of long-wavelength infrared radiation to short-wavelength infrared or visible radiation based on a quantum-well structure has been proposed and considered theoretically.
A monolithic wavelength converter of long-wavelength infrared radiation to short wavelength infrared or visible radiation based on a quantum-well structure has been proposed and considered theoretically. The quantum-well converter utilizes intersubband electron transitions in the emitter quantum well. The threshold intensity of long-wavelength infrared radiation necessary for the laser generation is evaluated as a function of the device structural and physical parameters.
A novel device -- the quantum-wire infrared phototransistor -- is proposed and evaluated. It is shown that this device can surpass in the performance the quantum-well phototransistor.
The purpose of the present work is to propose and evaluate two-terminal and three-terminal QW laser-phototransistor structures, which can generate a laser radiation in short-wavelength infrared range of spectrum modulated by long-wavelength infrared radiation. The analytical model of the two-terminal and three-terminal QW laser phototransistors is developed. The estimates show that the proposed QW laser-phototransistor can effectively operate in the range of modulation frequencies $f \geq 10$ GHz.
In this paper we present the picture of the physical effects in the quantum well infrared photodetectors (QWIPs) utilizing intersubband electron transitions. Our study is based on the numerical model, which allows one to find the distributions of the physical quantities in the QWIP structure and to calculate the external device characteristics. The operation of QWIP is associated with the nonuniform distribution of the potential and other related physical quantities. We show that contact and distributed effects play an important role in determining the operation and characteristics of the QWIPs.
Intersubband quantum-well infrared phototransistors (QWIPTs) based on Si/SiGe QW heterostructure of $p$-type are considered theoretically. An intentional nonuniformity of the QW doping, random fluctuations of acceptors in the QW and features of the hole spectrum are taken into account.
The effect of random fluctuations of the donor density in the quantum well of an intersubband single quantum-well infrared phototransistor (QWIPT) with triangular emitter and collector barriers is studied theoretically. It is shown that the fluctuations of the donor distribution in the plane of the QW can significantly increase the dark current. It reduces the photocurrent--to--dark ratio and detectivity.
This work deals with novel two-terminal and three-terminal QW laser-phototransistors, which can generate a laser radiation in short-wavelength infrared range of spectrum modulated by long-wavelength infrared radiation. The operation of the laser-transistors in question is connected with the injection of hot electrons into a laser active region or their extraction from it controlled by the potential of the QW specially inserted in the emitter or collector region. The mechanism of the modulation under consideration is compared with that associated with the heating of the electrons by infrared radiation.
In this paper we present the results of theoretical study of static and dynamic properties of multiple quantum well infrared photodetectors (QWIPs). This study is based on the original model of the QWIPs describing the electron injection from the emitter, transport in the QW structure, and capture (emission) in the QWs in a self-consistent manner. Both static and transient characteristics of the QWIPs are dominated by the contact effects associated with the recharging of the QWs under the applied voltage or infrared radiation.
Semiconductor quantum-well (QW) heterstructure can serve as a sensitive element in intersubband infrared photodetectors. In this work a novel infrared photodetector - quantum-dot (QD) infrared phototransistor - is proposed and evaluated. It is shown that the QD infrared phototransistors can surpass the phototransistors based on the QW structure due to their sensitivity to normal-incident radiation, low dark current and high photoelectric gain.
In this work we propose and evaluate novel infrared photodetectors -- the multiple quantum-dot (QD) infrared phototransistors. An analytical model of the QD infrared phototransistors is developed and implemented to evaluate their performance. The effects of the electron density fluctuations and electron crystal formation in the case of weak filling of the QD base are also discussed.
A novel infrared photodetector utilizing intersubband electron transitions - the superlattice infrared phototransistor (SLIPT) - is proposed and considered. The SLIPT comprises a two-dimensional SL inserted into undoped region sandwiched by doped layers playing a role of the emitter and collector. The SL services as the SLIPT base which replaces a quantum-well structure in a conventional quantum-well infrared phototransistor (QWIPT). It is supposed that the SL is formed by a two-dimensional array of weakly coupled quantum dots. The performance of the SLIPT is evaluated and the optimized version of the latter is compared with the QWIPT. It is shown that the SLIPT can significantly surpass the QWIPT in performance.
An injection heterostructure laser incorporated a resonant-tunneling structure (RTS) is studied theoretically. The laser under consideration consists of a heterostructure with vertical electron and lateral hole injection. The RTS is intended for the extraction of the electrons from the active region of the laser and it is controlled by an additional (third) terminal. The electron extraction through the RTS results in the decrease of the electron density and increase of their effective temperature. This effect is proposed to use for fast modulation of laser radiation. The modulation efficiency and maximum frequency of modulation are evaluated. The bistability effect associated with a mobile electron space charge behind the RTS and its influence on the laser controllability are also considered.
We report the theoretical study of high-frequency performance of single quantum well (QW) infrared phototransistor. The structure of the phototransistor comprises a floating base formed by a single QW, which is separated from the emitter and collector contacts by triangular barriers providing thermionic electron transport. The current is modulated by infrared radiation through intersubband absorption and resulting variation of the QW base potential. We obtain analytical expressions for the modulation efficiency as a function of infrared radiation intensity and frequency. The modulation by infrared radiation can be very fast, with maximum modulation frequency exceeding 10 GHz. Integration of infrared phototransistor with light emitting devices allows an efficient method of modulation of output radiation by long-wavelength infrared radiation.
A three-terminal semiconductor laser incorporated a resonant-tunneling structure which serves for the electron extraction from the laser active region is studied theoretically. Both electron concentration and heating effects in the active region are taken into account. It is shown that the laser can exhibit the voltage-controlled bistability.
The purpose of this paper is theoretical and experimental study of effects responsible for nonlinearity of quantum well infrared photodetectors (QWIP) photoresponse. Influence of QWIP structural parameters on nonlinear effects are discussed and design solutions to prevent the degradation of responsivity are proposed.
The modulation of laser radiation in a three-terminal laser incorporated a resonant-tunneling controlling structure is studied using an analytical model. It is shown that the modulation method under consideration can be very efficient and fast, in particular, due to the electron heating effects and high sensitivity of the resonant-tunneling current to the controlling voltage.
Three-terminal injection lasers with a resonant-tunneling structure are considered theoretically. It is shown that the lasers can be effectively controlled by voltage due to electron heating and cooling by electron extraction via resonant-tunneling structure.
High-speed performance of quantumwell infrared photodetectors (QWIPPs) are studied using numerical modeling. QWIP's response consists of two transients; a fast transient is due to combination of carrier transit and capture effects, and a slow transient is governed by QW's recharging processes.
Electron extraction and injection can provide a fast heating of the electron gas in the active region of three-terminal semiconductor lasers with a resonant-tunneling structure (RTS). Due to strong dependence of the optical gain on the electron temperature this mechanism can be used for a high-speed control of laser generation.
In this paper we evaluate novel infrared phototransistors - the quantum-wire infrared phototransistor (QRIP) and the quantum-dot infrared phototransistor (QDIP). Their performances are compared with that of the QWIP.
A nonstationary response of the multiple quantum-well infrared photodetectors is investigated using a computer simulation based on previously developed physical and numerical models. It is shown that there are two specific frequency ranges of interest, the first one is related to the carrier transit and capture processes, the second one - to the recharging of the quantum wells.
High-frequency characteristics of a quantum well (QW) diode with thermionic electron transport are reported in this paper. The frequency -dependent admittance of the QW diode is obtained in an analytical using the rigirous self-consistent small-signal analysis. The frequency dependences of the QW diode capacitance and conductance are governed by a characteristic time of the recharging of the QW, which depends strongly on temperature and device structural parameters. Experimental data on conductance and capacitance of the QW diode as functions of temperature and frequency can be used to extract the parameters of the QW, such as QW recombination velocity and ionization energy.