Resonant Tunneling Bipolar Transistors Research Articles

A comparative study of GaAs- and InP-based superlattice emitter resonant tunneling bipolar transistors (SE-RTBT's)

The InP/InGaAs and InGaP/GaAs superlattice emitter resonant tunneling bipolar transistors (SE-RTBTs) have been fabricated and demonstrated. By the employment of five-period superlattice in the emitter layer, the RT effect in saturation regime is observed at 77 K for InP/InGaAs SE-RTBT. In addition, due to the larger valence band discontinuity ΔE V at InGaP/GaAs heterojunction, the RT effect is observed both in saturation and forward active regimes at 300 K for InGaP/GaAs SE-RTBT. The confinement effect for minority carriers is enhanced due to the insertion of superlattice. The common emitter current gains up to 170 and 220 are observed for InP/InGaAs and InGaP/GaAs SE-RTBTs, respectively. Lower offset voltages of about 125 mV are observed in the studied devices.

MOCVD grown InGaP/GaAs multiple negative-differential-resistance (MNDR) resonant-tunneling bipolar transistors

We propose two InGaP/GaAs resonant tunneling bipolar transistors (RTBT's) with different superlattice (SL) structures in the emitters. Based on the calculations of transmission probability, the ground-state and first excited-state minibands are estimated. The electron transmission through SL structures is significantly determined by the electric field behaviors across the barriers. The specific designs of barrier width in the SL structures are responsible for two electron transport mechanisms of sequential RT conduction associated with the minibands. Experimentally, at higher current levels, the double- and quaternary-negative difference resistance (NDR) phenomena are respectively observed for both devices at 300K. Furthermore, the experimental results are in good agreement with the theoretical prediction.

On the multiple negative-differential-resistance (MNDR) InGaP-GaAs resonant tunneling bipolar transistors

Two InGaP/GaAs resonant tunneling bipolar transistors (RTBTs) with different superlattice (SL) structures in the emitters are fabricated and studied. The uniform and modulated widths of barriers are respectively utilized in the specific SL structures. Based on the calculations, the ground state and first excited state minibands are estimated from the transmission probability. The electron transport of RT through SL structures is significantly determined by the electric field behaviors across the barriers. Experimentally, the excellent transistor characteristics including the small saturation voltage, small offset voltage and high breakdown voltages are obtained due to the insertion of /spl delta/-doping sheet at the base-collector (B-C) heterointerface. Furthermore, at higher current regimes, the double- and quaternary-negative difference resistance (NDR) phenomena are observed in agreement with the theoretical prediction at 300 K.

Observation of the resonant-tunnelling effect andtemperature-dependent characteristics of an InP/InGaAs heterojunctionbipolar transistor

The temperature-dependent characteristics of anInP/InGaAs superlattice-emitter resonant-tunnelling bipolartransistor have been studied and demonstrated. Due to the useof a five-period InP/InGaAs superlattice, the RT effect isobserved at cryogenic temperature. In addition, the temperature-dependent dccharacteristics of the studied device from room temperature to 398 K arereported. Dc current gain remains at an approximately constant value overthe measured temperature range. The temperature coefficients ofbase-emitter and base-collector turn-on voltages are -2and -3 mV K-1, respectively. The ideality factors of base current(nB) and collector current (nC) exhibitnegative temperature coefficients. nB≈1indicates that the bulk base recombination current componentdominates the whole base current as the temperature isincreased.

NAND/NOR logic circuit using single InP-based RTBT

Bias dependent NAND and NOR logic functions using a single InP-based resonant tunnelling bipolar transistor (RTBT) are presented. NAND and NOR functionality is experimentally demonstrated and compared to simulation results using HP-MDS-software for the first time. The circuit benefits from the high breakdown voltage of the fabricated RTBT.

Tunneling devices and applications in high functionality/speed digital circuits

Tunneling phenomena can be used to realize devices with unique I-V characteristics (negative differential resistance) which can be employed to design various types of digital circuits with a significantly lower number of transistors, extremely fast switching speeds, very low power consumption and pipelining capability at the basic gate level (nanopipelining) which results in higher system throughput. In this article, we will present the basic properties of various types of devices which have been proposed for these applications including resonant tunneling diodes (RTDs), Esaki tunnel diodes (ETDs), and various types of transistors including resonant hot electron transistors (RHETs) and tunneling bipolar transistors (TBTs). We will also compare the anticipated performance of various types of logic gates and digital circuit implementations utilizing these devices with conventional CMOS circuits.

A self-consistent model to simulate large-signal electrical characteristics of resonant tunneling bipolar transistors

A model is presented which calculates the collector and base current densities for resonant tunneling bipolar transistors. This method combines the voltage-current relations for a heterojunction bipolar transistor and a resonant tunneling structure in a self-consistent manner to obtain the overall behavior of a resonant tunneling transistor. The model includes space-charge effects in the quantum well and predicts bistability in the current-voltage behavior, and is in good agreement with the experimental data reported on AlGaAsGaAs resonant tunneling transistors.

Resonant-Tunneling Bipolar Transistors with a Quantum-Well Base

Heterostructure bipolar transistors with a quantum-well base incorporated a resonant-tunneling structure in the collector are proposed and studied theoretically. Static characteristics of the transistors are evaluated using the proposed analytical model. It is shown that the current-voltage characteristics and the collector current versus base current dependences can be ambiguous corresponding to bistability operation. The bistability effect is associated with the mobile electron space charge in the collector region. Direct on–off switching by the collector voltage or base current pulses is discussed.

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.

The use of organometallic group-V sources for the metalorganic molecular beam epitaxy growth of In 0.48Ga 0.52P/GaAs and In 0.53Ga 0.47As/InP heterojunction bipolar device structures

This paper describes the use of tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) as replacements for arsine and phosphine in MOMBE/CBE for the production of device structures with state-of-the-art performance. The growth system used for this work is based on the use of elemental group-III and dopant sources, and employs thermal crackers for the low pressure precracking of TBA and TBP. Device structures fabricated in the In 0.48Ga 0.52P/GaAs materials system include single- and double-heterojunction bipolar transistors (SHBTs and DHBTs). Current gains as high as 2690 have been obtained with these transistors. Deep level transient spectroscopy (DLTS) measurements of the emitter-base junctions of these transistors reveals the absence of deep level traps, in contrast to similar devices fabricated using AlGaAs/GaAs. Device structures fabricated in the In 0.53Ga 0.47As/InP materials system include SHBTs, DHBTs, and resonant tunneling bipolar transistors (RTBTs). In 0.53Ga 0.47As/InP SHBTs with record maximum oscillation frequencies (ƒ max) of > 180 GHz have been produced with high breakdown voltages BV CEO and BV CBO of 8.1 and 17 V, respectively. In addition, DHBTs with ƒ T=134 GHz and ƒ max=137 GHz have been fabricated. Resonant tunneling bipolar transistors, consisting of a structured AlAs/In x Ga 1− x As resonant tunneling double barrier vertically integrated into the emitter of an InP/InGaAs double heterojunction bipolar transistor structure, have been demonstrated. These transistors have room temperature peak-to-valley current ratio of approximately 20, current gain of 100, and breakdown voltage exceeding 5 V, allowing the demonstration of the first room temperature resonant tunneling transistor integrated circuits.

Co-integration of resonant tunneling and double heterojunction bipolar transistors on InP

The authors report the first co-integration of resonant tunneling and heterojunction bipolar transistors. Both transistors are produced from a single epitaxial growth by metalorganic molecular beam epitaxy, on InP substrates. The fabrication process yields 9- mu m/sup 2/-emitter resonant tunneling bipolar transistors (RTBTs) operating at room temperature with peak-to-valley current ratios (PVRs) in the common-emitter transistor configuration, exceeding 70, at a resonant peak current density of 10 kA/cm/sup 2/, and a differential current gain at resonance of 19. The breakdown voltage of the In/sub 0.53/Ga/sub 0.47/As-InP base/collector junction, V/sub CBO/, is 4.2 V, which is sufficient for logic function demonstrations. Co-integrated 9- mu m/sup 2/-emitter double heterojunction bipolar transistors (DHBTs) with low collector/emitter offset voltage, 200 mV, and DC current gain as high as 32 are also obtained. On-wafer S-parameter measurements of the current gain cutoff frequency (f/sub T/) and the maximum frequency of oscillation (f/sub max/) yielded f/sub T/ and f/sub max/ values of 11 and 21 GHz for the RTBT and 59 and 43 GHz for the HBT, respectively. >

Room-temperature resonant tunnelling bipolar transistor XNOR and XOR integrated circuits

The first resonant tunnelling bipolar transistor integrated circuits operating at room temperature are demonstrated. The circuits are composed of cointegrated resonant tunnelling bipolar transistors and double heterojunction bipolar transistors based on InP substrates. Both a three-transistor XNOR and a seven-transistor XOR logic gate have been demonstrated using a 3 V power supply.

Resonant Tunnelling Bipolar Transistor (RTBT): New Functional Device for Electronics of the Future

The development of Resonant Tunnelling Bipolar Transistor (RTBT), including multi-state RTBTs and their circuit applications are reviewed in this paper. Multi-state RTBTs, designed using the concept of sequential quenching of resonant tunnelling in a multiple quantum well structure, paved the path for novel circuits, such as the implementation of multiple valued logic. The complexity of conventional logic and signal processing circuits are also reduced by the use of RTBTs. Finally, recent results on superlattice-base transistors and their possible application potentialities are also discussed.

The effect of incident momentum distribution function on the current-voltage characteristic of resonant tunneling double barriers

Resonant tunneling of nonequilibrium electrons through double barriers as obtained by injection with a ballistic launcher is investigated. It is shown that a large peak-to-valley ratio in the tunneling current can be obtained only if the incident electron distribution in momentum space is anisotropic and strongly oriented along the normal to the double barriers with a well defined nonzero lower bound on the associated energy component. An isotropic distribution, on the other hand, will result in no current peak. We also discuss the effect of scattering in the region before the double barrier on broadening the peak and reducing the peak-to-valley ratio. This effect is stronger in the case of resonant tunneling through excited states of the double barriers. These considerations are important for the design of resonant tunneling bipolar transitors with nonequilibrium electron injection. Experimental results on the resonant tunneling bipolar transistors with a tunnel emitter and a double barrier in the base are reported. The collector current exhibits a peak as the emitter-base voltage is varied. The peak position is in agreement with the calculated value and the small peak-to-valley ratio is understood in terms of the effects described above.

Resonant tunneling bipolar transistors using InAlAs/InGaAs heterostructures

Resonant tunneling bipolar transistors (RBTs) using InAlAs/InGaAs heterostructures were fabricated. These devices are bipolar transistors which use a resonant tunneling barrier as a minority-carrier injector. The RBT exhibits a collector current peak as a function of the base-emitter voltage at room temperature. The peak-to-valley ratio of the collector current is 3.5, and the peak collector current density is 5.7×104 A/cm2. The common-emitter current gain reaches a value of 24. These InAlAs/InGaAs RBTs characteristics are much better than those of AlGaAs/GaAs RBTs. We measured the microwave characteristics of the InAlAs/InGaAs RBT at room temperature, and obtained a cutoff frequency of 12.4 GHz. An equivalent circuit analysis and device simulation yielded an estimated resonant tunneling barrier response time of 1.4 ps.

Quantum functional devices: resonant-tunneling transistors, circuits with reduced complexity, and multiple valued logic

Recent advances in the area of quantum functional devices are discussed. After a discussion of the functional device concept, resonant-tunneling bipolar transistors (RTBTs) with a double barrier in the base region are described. Design considerations for RTBTs with ballistic injection and the first observation of minority-electron ballistic RT are presented. RTBTs using thermionic injection and exhibiting a high peak-to-valley ratio at room temperature in the transfer characteristics are also described. Multiple-state RTBTs and their DC and microwave performance are then discussed. Circuit applications of RTBTs also are discussed. It is shown that RTBTs allow the implementation of many analog and digital circuit functions with a greatly reduced number of transistors and show considerable promise for multiple-valued logic. Experimental results on frequency multipliers and parity bit generators are presented. Analog-to-digital converters are memory circuits are also discussed. Two novel superlattice-base transistors are reported. Negative transconductance is achieved by suppression of injection into minibands. Gated quantum-well RT transistors are also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Resonant tunneling through quantum wells: Physics and device applications

Recent results on the physics and device applications of resonant tunneling (RT) are discussed. RT through parabolic quantum wells has been observed for the first time; up to fourteen resonances have been detected in one structure. The first ten correspond to RT through the quasi-bound-states of the parabolic well while the other ones are ascribed to electron interference effects associated with virtual levels in the quasi-continuum energy range above the collector barrier. A new hot-electron spectroscopy technique based on RT has been applied to the study of hot minority-electron injection in GaAs via band discontinuities. These results are important for the design of RT transistors. RT bipolar transistors and RT field effect transistors are discussed in the last section of the paper.

Parity generator circuit using a multistate resonant tunnelling bipolar transistor

A four-bit parity generator circuit using a single resonant tunnelling bipolar transistor (RTBT) exhibiting two negative transconductance regions in the characteristics, is demonstrated. The circuit uses only one transistor as compared to 24 needed in conventional logic. The present circuit also provides significant advantages over previous parity generator circuits using resonant tunnelling diodes. The same circuit, when used with only two input bits, will act as an exclusive-NOR gate.

Physics and New Device Applications of Resonant Tunneling in Quantum Well Heterostructures

Recent advances in quantum well (QW) tunneling devices are discussed. These include resonant tunneling (RT) bipolar and field effect transistors; infrared lasers and detectors based on sequential RT and superlattice effective mass filters.