Resonant Tunneling Hot Electron Transistors Research Articles

High Magnetic Field Study of Ballistic Transport in a Resonant-Tunneling Hot-Electron Transistor (RHET)

Base and collector currents have been studied in an InAlAs/InGaAs resonant-tunneling hot electron transistor at 4.2 K in pulsed magnetic fields up to 42.5 T. Base and collector currents have been found to depend strongly on the field and its orientation. For fields perpendicular to the current direction, the base/emitter current ratio increases initially with an approximate parabolic dependence and then saturates at high fields. From this magnetic field dependence, scattering processes in the InGaAs base region are discussed. Using a classical model for electron transport under a magnetic field perpendicular to the current, values for the mean free path and scattering time in the base are obtained that agree well with theoretical values for electron-electron scattering. It is shown that the magnetic field dependence of the collector current at high perpendicular fields can be explained by single barrier tunneling. A model in WKB approximation allows to determine the electron energy. Moreover, by extrapola...

Compact multiple-valued multiplexers using negative differential resistance devices

Quantum electronic devices with negative differential resistance (NDR) characteristics have been used to design compact multiplexers. These multiplexers may be used either as analog multiplexers where the signal on a single select line selects one out of four analog inputs, or as four-valued logic multiplexers where the select line and the input lines represent one of four quantized signal values and the output line corresponds to the selected input. Any four-valued logic function can be implemented using only four-valued multiplexers (also known as T-gates), and this T-gate uses just 13 devices (transistors) as compared to 44 devices in CMOS. The design of the T-gate was done using a combination of resonant tunneling diodes (RTD's) and heterojunction bipolar transistors (HBT's) with the folded I-V characteristic (NDR characteristic) of the RTD's providing the compact logic implementation and the HBT's providing the gain and isolation. The application of the same design principles to the design of T-gates using other NDR devices such as resonant tunneling hot electron transistors (RHET's) and resonant tunneling bipolar transistors (RTBT's) is also demonstrated.

Multiple Negative Differential Resistance due to Quantum Interference of Hot Electron Waves in Metal (CoSi 2)/Insulator (CaF 2) Heterostructures and Influence of Parasitic Circuit Elements

We report the observation of multiple negative differential resistance (NDR) in a metal (CoSi2)/insulator (CaF2) resonant tunneling hot electron transistor structure. Multiple NDR observed here can be attributed to the modulation of the transmission probability of hot electron waves due to quantum interference in the conduction band of the insulator (CaF2) collector barrier layer between two metal (CoSi2) layers. By reducing the influence of the Schottky diode at the CoSi2/Si interface, relatively clear and low-voltage NDR is observed. It is found, by a simulation including parasitic elements, that the collector resistance and leakage current greatly influence the current voltage characteristics.

Integration of resonant-tunneling transistors and hot-electron transistors

We have integrated a tunneling hot-electron transfer amplifier (THETA) and a novel resonant-tunneling hot-electron transfer amplifier (RTHETA) within a single epitaxial growth. At room temperature, the THETA exhibits a common-emitter current gain of greater than six and a voltage swing of 800 mV when measured in an inverter configuration. The RTHETA exhibits similar common-emitter current gain and a four-state voltage transfer characteristic with an output voltage swing of 1 V. In contrast to the resonant-tunneling hot-electron transistor (RHET), the RTHETA exhibits current gain both before and after the resonant peak voltage. From on-wafer S-parameter measurements, the current-gain cut-off frequency (f/sub T/) and the maximum frequency of oscillation f/sub max/) for both transistors are approximately 20 GHz and 9 GHz, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Realization of a novel resonant-tunneling hot-electron transistor: Competition of ultrafast resonant-tunneling and energy relaxation

We report a novel three-terminal hot-electron transistor, where at 77 K the transistor output characteristics can display novel features, including the negative differential resistance, extremely large peak-to-valley ratio, and a d.c. current gain. The operation of this novel transistor is based on quantum tunneling. The emitter injects hot-electrons to the second lowest subband of a thin (100 Å) quantum well, and these non-thermalized hot-electrons will then either resonantly tunnel to the collector or relax to the lowest subband and contribute to the base current. The resonant-tunneling probability of hot-electrons between the emitter and the collector can be switched almost completely on and off, when either the base or the collector bias is swept. The new characteristics are shown to have application in dense logic circuits.

The growth of resonant tunneling hot electron transistors using chemical beam epitaxy

A systematic growth study of InGaAs/AlAs/InGaAsP resonant tunneling hot electron transistors (RHETs) was performed using chemical beam epitaxy (CBE). The resonant tunneling hot electron transistors studied consist of a highly strained AlAs/In 0.75Ga 0.25As/AlAs double barrier structure and an undoped InP collector barrier with 1.1 and 1.2 μm InGaAsP graded layers. These quaternaries were lattice matched to InP within 2.6×10 −4 and showed an averaged full width at half-maximum (FWHM) of 6 meV from low temperature photoluminescence (PL) measurement. The effects of growth interrupt were studied using PL, X-ray diffraction and secondary ion mass spectrometry (SIMS) measurements. It was found that excessive growth interrupt induced high oxygen accumulation (8×10 18 cm −3) at the heterojunction and reduced the intensity of PL spectra. Moreover, for the growth of tunneling heterostructures, low substrate temperature, appropriate growth interrupts and use of hydride drying filters and high purity hydrides were helpful to improve device performance. The highest peak-to-valley current ratio (PVR) observed was 12.7, and maximum base transport ratio was 0.98 at 80 K. Furthermore, some digital functions such as flip-flop gate and exclusive NOR were demonstrated using a single RHET.

InGaAs/AlAs/InGaAsP resonant tunneling hot electron transistors grown by chemical beam epitaxy

InP-based resonant tunneling hot electron transistors (RHET's) were studied systematically using chemical beam epitaxy (CBE) for the first time. All the RHET's studied have a highly strained AlAs/In/sub 0.75/Ga/sub 0.25/As/AlAs resonant tunneling double barrier as a hot electron injector, and an InP collector barrier with or without InGaAsP graded layers. The highest transport ratio (/spl alpha/) observed is 0.98, and the highest peak-to-valley current ratios (PVR's) measured are 20 and 200 in the collector current and base current, respectively, at 80 K. A self-consistent simulation is used as a reference to optimize the hot electron injector and to explain the ballistic transport. An energy spectrometer technique was applied to the RHET's for resolving the hot electron energy distribution which showed a full width at half maximum (FWHM) of around 58 meV, indicating ballistic transport of electrons. Finally, room temperature transistor action was also observed with a /spl beta/ of 4 and a cutoff frequency of 31 GHz. >

A Static Random Access Memory Cell Using a Double-Emitter Resonant-Tunneling Hot Electron Transistor for Gigabit-Plus Memory Applications

This paper describes our research on quantum memory devices having a single transistor structure similar to that of a double-emitter resonant-tunneling hot electron transistor (RHET). Its prototype 2×2 bit cell array was fabricated and operated at room temperature. The device used in the prototype cell had no current gain, however, and required other active devices to build static random access memory (SRAM) peripheral circuits such as a decoder and senseamplifier. We also report recent advances in the memory cell made using a double-emitter RHET which has a current gain of 8 at 77 K–suitable for logic circuits peripheral to our memory cell array. The cell's small size shows promise for use in large scale memory application.

Room-temperature operation of InGaAs-based hot-electron transistors

It is demonstrated that 300-K operation of an InGaAs-based HET (hot-electron transistor) can be achieved by further increasing the electron injection energy in combination with the use of a wide-bandgap base-collector isolation barrier. The characteristics of a device consisting of an InAlAs emitter, a 10-AA AlAs tunnel-barrier positioned at the emitter-base heterojunction, a 400-AA n+ InGaAs base region, and a 2500-AA InAlGaAs collector barrier are reported. The injected electrons are transported across the base region with over 80% efficiency, as measured in a common-base configuration. The maximum common-emitter current gain in this nonoptimized transistor is nearly four with an f/sub T/ of over 40 GHz and a base-collector breakdown voltage of 1.5 V. A systematic study of RHET (resonant tunneling HET) injector and collection properties indicates that the HET can operate at room temperature with a current gain on the order of 100. 300-K operation of a single-RHET, exclusive-NOR integrated circuit that is similar in design to the one demonstrated at 77 K by N. Yokoyama et al. (1985) is also shown.

Room-temperature operation of a resonant-tunneling hot-electron transistor based integrated circuit

The first resonant-tunneling hot-electron transistor (RHET) EXCLUSIVE-NOR integrated circuit that operates at room temperature is demonstrated. The XNOR circuit consisting of a single resonant-tunneling transistor and four thin-film resistors, exhibits a 500-mV output voltage swing between the high- and low-logic levels when biased with a 1.8-V supply. The transistor, which features a novel InGaP collector barrier, has a peak current density of 4*10/sup 4/ A-cm/sup -2/, a common-base transfer coefficient of 0.9, and a peak-to-valley current ratio of 10:1 when operated in a common-emitter mode.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-magnetic-field effects on a resonant-tunneling hot-electron transistor measured up to 40 T

Base and collector currents have been measured in a resonant-tunneling hot-electron transistor based on an InAlAs/ InGaAs heterostructure at 4.2 K in pulsed magnetic fields up to 42.5 T. Base and collector current strongly depend on the field and its orientation. Our observations are compared with the field dependence of the tunneling characteristic of double-barrier structures based on GaAs/(Al, Ga)As.

Novel Electronics Enabled by Rare Earth Arsenides Buried in III-V Semiconductors

ABSTRACTHeterostructures consisting of III-V semiconductors and epitaxial layers of the rare earth monoarsenides can be grown by molecular beam epitaxy. By alloying ErAs with ScAs, lattice match can be achieved with (Al,Ga)As. Using magneto-transport measurements, we show that these layers are semi-metallic with equal electron and hole concentrations, 3.0 ×1020 cm−3. Shubnikov-de Haas oscillations are used to confirm the predicted Fermi surface geometry and measure the electron effective mass and the coupling to the 4f spin on the Er3+ ion. Remarkably, the material shows no transition from semimetal to semiconductor as the film thickness is reduced to three monolayers. Below three monolayers the films are not uniform and are believed to consist of islands three monolayers high.This system provides a unique opportunity to explore novel electronics based on controlled transport through semimetal/semiconductor heterostructures. Lateral transport through semimetal islands immersed in a δ-doped layer may provide a fast non-linear material for THz electronics. Vertical transport through thin epitaxial layers may enable resonant tunneling hot electron transistors with a semi-metal base. Preliminary experiments on transistor like test structures measure some transfer through a 10 monolayer thick semimetal base. They also identify overgrowth of the III-V semiconductor on the semimetal layer as the key materials issue.

InGaAs/In(AlGa)As RHET's with InAs pseudomorphic base

An InGaAs/In(AlGa)As resonant-tunneling hot-electron transistor (RHET) with an INAs pseudomorphic base to increase current gain and to reduce base resistance was designed and fabricated. The conduction band discontinuity between the InAs base and the In(AlGa)As collector barrier was estimated from the thermionic current. The band discontinuity was about 0.38 eV, which agrees well with the calculated band discontinuity taking into consideration the effect of strain. The common-emitter current gain doubled and the base resistance decreased 20% compared to InGaAs-base RHETs with the same doping concentration. A current gain cutoff frequency of 65 GHz and a maximum oscillation frequency of 50 GHz at 77 K were measured. >

Logic circuits using resonant-tunneling hot-electron transistors (RHETs)

A full adder and a 1/2 frequency divider using resonant-tunneling hot-electron transistors (RHETs) are proposed. These circuits make the best use of negative differential conductance, a feature of RHETs, and contain much fewer transistors than used in conventional circuits. They were fabricated using self-aligned InGaAs RHETs and WSiN thin film resistors on a single chip. The RHETs have an i-InGaAlAs/i-InGaAs collector barrier that improves the current gain at low collector-based voltages. Circuit operation was confirmed at 77 K with a supply voltage of 3 V.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Room Temperature Hot Electron Transistors with InAs-Notched Resonant-Tunneling-Diode Injector

Room temperature operation is achieved in In(GaAl)As/InGaAs resonant-tunneling hot electron transistors (RHET) grown by molecular beam epitaxy on InP substrates. RHETs with base widths of 10, 40 and 60 nm are fabricated and all exhibit room temperature dc current gain greater than 2, with gain as high as 12 observed at resonance in the 40 nm base device. To our knowledge these are the first In(GaAl)As hot electron transistors to exhibit 300 K gain of this magnitude. In addition, the transistors also exhibit strong negative transconductance and a unique negative peak-to-valley current ratio. S-parameter measurements of the 40(60) nm base RHET give values for fT and fMAX of 67(54) and 41(11) GHz respectively.

Transient analysis of resonant tunneling hot electron transistor (RHET)

We made a transient analysis of an InGaAs/In(AlGa)As resonant tunneling hot electron transistor (RHET) using time-dependent ensemble Monte Carlo simulation. We simulated the transient characteristics of electron transport in the collector barrier region and the collector current of the RHET. We accounted for the hot electron current and displacement current. We found that the collector current delay is about half the transit time due to the displacement current.

Modeling electron transport in InGaAs-based resonant-tunneling hot-electron transistors

The modeling of the resonant-tunneling hot-electron transistor (RHET) is described. In an analysis of the resonant-tunneling barrier, the Schrodinger and Poisson equations are solved self-consistently. The electron transport in the base and the collector barrier region is simulated using the Monte Carlo method, taking account of the space charge in the collector barrier. The model used includes the effect of coupled plasmon-LO phonon scattering and electron-electron scattering in the base region. The transit time is calculated in the base and the collector barrier region. The 50-nm base transient time is 0.059 ps. On the other hand, the 200-nm collector barrier transit time is larger than 1 ps due to intervalley scattering in the collector barrier region. it is shown that the collector barrier transit time can be reduced to 0.089 ps in the 50-nm collector barrier RHET at a collector-base voltage of 0.5 V. >

Experimental analysis of resonant-tunneling hot-electron transistors operated at room temperature

The fabrication of AlAs/InGaAs resonant-tunneling hot-electron transistors (RHETs) operating at room temperature is reported. The device used for this study had a resonant-tunneling barrier consisting of a 26.4-AA InGaAs layer sandwiched by two 23.7-AA AlAs layers and a collector barrier of 2000-AA In/sub 0.52/Al/sub 0.48/As. These were grown on a semi-insulating InP substrate by MBE (molecular-beam epitaxy). The resonant-tunneling barrier exhibited negative differential resistance at room temperature, while the collector barrier was a good electrical isolator at room temperature. The collector current and base current were measured at room temperature as functions of base-emitter voltage with a constant 3 V on the collector in the common-emitter configuration. The current gain (and the differential current gain) increased with the base-emitter voltage, peaking at 0.64 V (0.56 V). As the base emitter voltage increased further, the current gain decreased. This is attributed to the intervalley scattering of electrons from the Gamma -valley to the L-valleys in the InGaAs base. The scattering parameters of the RHET were measured from 0.2 to 20.2 GHz using the collector current density as a parameter and analyzed using an equivalent RHET circuit. The high-frequency capacitance and conductance of the resonant-tunneling-barrier were determined to be 93.0 fF and 1.98 mS/ mu m/sup 2/, respectively, at a collector current density of 3.3*10/sup 4/ A/cm/sup 2/. The resonant-tunneling-barrier response time was 1.56 ps. >

Resonant tunneling hot-electron transistor with current gain of 5

By optimizing its structure, we have improved the current gain and collector-current peak-to-valley ratio of a resonant tunneling hot-electron transistor. The device has an asymmetric resonant tunneling barrier with an optimal well thickness to attain a higher peak-to-valley ratio for the collector current. Also, the device uses a graded collector barrier and decreased base thickness, exhibiting a common emitter current gain of 5.1 (at 77 K), the highest value ever reported for an AlGaAs/GaAs hot-electron transistor.