Real-space Transfer Transistor Research Articles

Monostable–Bistable Transition Logic Element Formed by Tunneling Real-Space Transfer Transistors With Negative Differential Resistance

We demonstrate three-terminal λ-type negative differential resistance (NDR) tunneling real-space transfer transistors (TRSTT) with InGaAs and a δ-doped GaAs dual-channel structure on a (100) GaAs substrate. The NDR mechanism is attributed to the electron tunneling transfer from a high-mobility InGaAs channel to a low-mobility δ-doped GaAs channel, as well as to a gate electrode through a Schottky cap layer. The maximum of the peak-to-valley current ratio and the transconductance of the peak current density (gm = ΔJP/ΔVGS) reach 3.3 and 72 mS/mm, respectively. The invert operation of MOBILE is realized by employing two TRSTTs connected in series at room temperature.

Design, fabrication and characterization of dual-channel real space transfer transistor

In this paper, using a δ-doping dual-channel structure and GaAs substrate, a real space transfer transistor (RSTT) is designed and fabricated successfully. It has the standard Λ-shaped negative resistance I–V characteristics as well as a level and smooth valley region that the conventional RSTT has. The negative resistance parameters can be varied by changing gate voltage (VGS). For example, the PVCR varies from 2.1 to 10.6 while VGS changes from 0.6 V to 1.0 V. The transconductance for IP (ΔIP/ΔVGS) is 0.3 mS. The parameters of VP, VV and threshold gate voltage (VT) for negative resistance characteristics arising are all smaller than the value reported in the literature. Therefore, this device is suitable for low dissipation power application.

Blue sky in SOI: new opportunities for quantum and hot-electron devices

The combination of silicon-on-insulator (SOI) substrates with ultrathin Si and insulator layers opens new opportunities for quantum effect and hot-electron devices. Unlike their III–V predecessors, these devices have the crucial advantage of potential integrability with dominant silicon technology. We discuss three examples of such SOI devices: a three-terminal real-space transfer transistor with a low-barrier dielectric; a vertical tunneling transistor with an ultrathin tunneling gate oxide; and a lateral interband tunneling transistor. None of these devices has progressed beyond a rudimentary proof-of-concept demonstration, but the strong nonlinearities of their characteristics deriving from quantum tunneling or hot-electron injection, as well as their unique scaling behavior, make them an interesting playground for innovative device research.

Voltage-Controlled Small Signal Analysis of Real Space Transfer Transistor

The research of determining the small signal equivalent circuit of the real space transfer (RST) transistor is investigated in this work. We propose a voltage-controlled mode model, called parameter extraction, to describe the performance of RST transistors at high frequency range. Besides, we also employ the value-determined model to simulate the microwave characteristics of RST and the theoretical and experimental results are compared. The influence of variables of RF performance is analyzed and theoretical results show that the cut-off frequency(fT)is mainly affected by the leakage resistances and the dimension of metal contact, but the maximum available gain frequencyfmax, is dependent on contact resistances.

DC and AC Characteristics of GaAs/InGaAs/AIGaAS Real Space Transfer Transistors

DC and AC performances of a GaAs/InGaAs/AIGaAs negative resistance field-effect transistor (NERFET) are demonstrated by molecular beam epitaxy (MBE) for the first time. The negative differential resistance (NDR) resulted from the observation of the hot electron real space transfer effect in InGaAs channel. By Hall measurements, the structure shows carrier mobility as high as 4300 (13500) cm2/v-s at 300 (77)K, which is suitable for high frequency operation. For DC performance, the largest peak-to-valley current ratio of the device is about 5 at room temperature. For AC performance, S-parameter measurements of high frequency and microwave characteristics indicate a projected maximum frequency of oscillation offmax⁡=2.7GHzand a current gain cutoff frequency (fT) occurs at 1.8GHz.

Applications of multi-functional characteristics in GaAs/AlGaAs field effect real space transfer transistors

Electrically alterable functionality, including bi-phase modulation and signal demultiplexing, is demonstrated in a field effect real space transfer transistor. The ability to express widely different functional characteristics as a result of gate modulated real space transfer permits energy multiplexing of device functionality within a single physical structure.

Enhanced real-space transfer in δ-doped GaAs/In0.1Ga0.9As/In0.25Ga0.75As two-step channel heterojunctions

A two-step channel In0.1Ga0.9As/In0.25Ga0.75As heterostructure real-space transfer transistor grown by low-pressure metalorgonic chemical vapor deposition is implemented. By virtue of δ doping, shallow ohmic contacts and two-step channel, a high peak-to-valley current ratio up to 260 000 at 300 K can be obtained at low collector voltage (Vc=3 V). Moreover, from Shubnikov–de Haas (SdH) measurements, we observe a positive persistent-photoconductivity effect and variations of quantum lifetime. The SdH result is in good agreement with the critical drained-to-source onset voltage of negative differential resistance.

Field effect real space transfer transistor

We report demonstration of the first field effect real space transfer transistor (FERST), a gated real space carrier transfer device. It is a dual output, multifunctional device which, depending on region of operation, demonstrates either of three characteristics: traditional FET transconductance, sign reversing transconductance, or dual output with near complimentary transconductances. Additionally, the FERST structure provides a new means for exploring the physics of real space transfer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A novel /spl delta/-doped GaAs/lnGaAs real-space transfer transistor with high peak-to-valley ratio and high current driving capability

A three-terminal /spl delta/-doped GaAs/In/sub 0.25/Ga/sub 0.75/As/GaAs real-space transfer transistor (RSTT) has been implemented by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) for the first time. We carried out an ohmic recess resulting in shallow alloyed contacts, electrically isolated from ohmic electrodes. An undoped low-growth-rate buffer layer was inserted between the collector and barrier to suppress the dopant out-diffusion from the substrate to the barrier. The proposed device with a 5×100 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> emitter channel revealed an extremely sharp charge injection, a broad valley range (>5 V), a high peak-to-valley current ratio up to 430000, and a high current driving capability at room temperature. These characteristics are, to our knowledge, among the highest reported values to date.

High performance three-terminal δ-doped GaAs negative resistance field-effect transistor based on real-space transfer

A three-terminal delta -doped GaAs real-space transfer transistor has been demonstrated by low-pressure metal organic chemical vapour deposition for the first time. The device has the advantages of: ease of growth and fabrication, large and adjustable peak-to-valley current ratio even at room temperature, extremely sharp charge injection, high transconductance, and high-power handling capability.

Microwave performance of top-collector charge injection transistors on InP substrates

Charge injection transistors have been implemented in molecular beam epitaxy grown InGaAs/InAlAs/InGaAs and InGaAs/InP/InGaAs heterostructures using a self-aligned process for the collector stripe definition. Scattering parameters have been measured in the frequency range from 100 MHz to 40 GHz. InP barrier devices show the best microwave performance ever reported for a real-space transfer transistor: at 40 GHz the short circuit current gain mod h21 mod is 8 dB and the power gain is larger than unity. The slope of mod h21(f) mod depends on the bias point and is generally gentler than 20 dB decade-1. Extrapolating at the measured slope, we find mod h21 mod =1 at f=115 GHz. The short circuit current gain cut-off fT, defined by extrapolation at 20 dB decade-1 from the point of least mean square deviation of the measured slope from 20 dB decade-1, is fT=73 GHz. Devices with InA/As barriers show a relatively slower performance (fT=32 GHz). The difference is discussed in terms of the relative rates of intervalley scattering and real-space transfer in the two heterostructures.

Real-space transfer by hot electron resonant tunneling

Demonstrations of real-space transfer transistors have primarily shown real-space transfer current due to thermionic emission of heated channel electrons over low heterostructure barriers. In this paper we demonstrate real-space transfer of hot electrons due to resonant tunneling through multiple AlAs/GaAs/AlAs double barrier structures.

Monte Carlo simulation of real-space transfer transistors: device physics and scaling effects

Monte Carlo simulations of the real-space transfer transistor (RSTT) are carried out for various bias conditions. Detailed analysis of the RSTT, especially in the saturation regime, is performed. The mechanism responsible for the saturation of the source current is explained in terms of reverse real-space transfer. The operation of the RSTT is compared with that of the charge injection transistor and it is pointed out that the difference in geometry of these two devices leads to different physical operation. The effect of reducing the device dimensions on the RSTT performance is discussed. A reduction in the collector length is found to improve the transconductance. Transient analysis of the RSTT shows that the device with a smaller collector length would exhibit higher cutoff frequencies. A reduction in the width of the collector drift region is shown to result in an increased peak-to-valley ratio in the heater current which makes the drive more efficient for microwave generation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Monte Carlo simulation of InGaAs/AlGaAs/GaAs real-space transfer transistors

Three-terminal devices based on real-space transfer (RST) of heated electrons across heterointerfaces, are promising for applications at microwave frequencies. Recently, a real-space transfer transistor (RSTT) similar to the charge injection transistor (CHINT), but with a pseudomorphic InGaAs/AlGaAs/GaAs material system and a collector-up structure has been demonstrated, exhibiting a 60 GHz gain-bandwidth product. The authors analyse the RSTT of Hueschen and coworkers using a self-consistent ensemble Monte Carlo technique. In particular, they focus on the location of RST with respect to the source-to-collector distance. They also propose an RSTT structure with an additional 'gate' electrode for response to changes in the heater voltage.

Symmetry of the real-space transfer and collector-controlled states in charge injection transistors

The charge injection transistor, or CHINT, is a three-terminal semiconductor device based on controlled real-space transfer of hot electrons between two conducting layers separated by a potential barrier. The symmetry of hot-electron injection by real-space transfer with respect to the polarity of the heating field allows the implementation of novel circuit elements. Thus, in the basic CHINT structure, the collector current is an exclusive OR function of voltages applied to the emitter electrodes. Moreover, the authors have proposed and demonstrated a multiterminal device structure with three symmetric logic inputs that performs both the NOR and the AND logic functions, and can be switched between these functions in the course of the circuit operation. Symmetry properties of real-space transfer transistors have been studied theoretically, with the help of continuation modeling and transient device simulation. These studies reveal a variety of instabilities and a striking novelty of multiply connected current-voltage characteristics. The authors have found that the CHINT can support anomalous steady states in which hot-electron injection occurs in the absence of any voltage between the emitter electrodes. In these states, some of which are not only stationary but also stable with respect to small perturbations, the electron heating is due to the fringing field from the collector electrode. Some of the anomalous states break the reflection symmetry in the plane normal to the channel at midpoint. The study elucidates the formation of hot-electron domains.

Ensemble Monte Carlo simulation of real space transfer (NERFET/CHINT) devices

The first self-consistent particle-field ensemble Monte Carlo model for real space transfer (NERFET/CHINT) devices will be presented. The simulations performed are in agreement with experiments and reproduce all prominent features of NERFET/CHINT structures such as, negative differential resistance, saturation of drain and substrate (injection) current at high source-to-drain voltages, and the negative transconductance ( ΔI D, sat / ΔV sub < 0) in the saturated drain current Negative differential resistance (NDR) can be achieved through real-space electron transfer which is based on the emission of electrons from one semiconductor layer into another semiconductor layer in the presence of high electric fields parallel to the layers (Hess, 1979). The major advantage of this mechanism over the Gunn effect is that the material parameters such as mobility ratios of adjacent layers, barrier heights, layer thicknesses can be engineered to control peak-to-valley ratios, device speeds and NDR threshold voltages. Recently a number of devices, namely negative differential resistance field effect transistor (NERFET) and charge injection transistor (CHINT), have been proposed and experimentally verified (Luryi, 1985). The purpose of this paper is to present our Monte Carlo model for the real space transfer transistors (NERFET/CHINT) and summarize our simulations which are in agreement with experiments.

Ensemble Monte Carlo simulation of velocity modulation transistors (VMT) and real space transfer (NERFET, CHINT) devices

Numerical simulation of velocity-modulation field effect transistors and real-space transfer transistors are presented. Using self-consistent particle-field Monte Carlo analyses, we assess possible advantages of these novel device structures with respect to their switching speed. Our study shows that current switching can be achieved by the velocity modulation concept. The simulations performed for real space transfer devices are in agreement with experiments and reproduce all prominent features of real space transfer structures such as, negative differential resistance, saturation of drain and substrate (injection) current at high source-to-drain voltages, and the negative transconductance ( Δ I D,sat Δ V sub <0 ) in the saturated drain current.