Clear negative characteristics observed in coupled-quantum-wellbase resonant tunneling transistors

Clear negative resistance characteristics observed in a resonant tunneling transistor with a coupled-quantum-well (CQW) base are reported. The collector current reveals negative resistance properties with respect not only to the base-emitter voltage but also the base current in the common-emitter configuration. The collector current peak-to-valley ratio is enhanced in the CQW-base transistor compared with a reference transistor with a single-quantum-well (SQW) base     

Picosecond-switching time ofIn0.53Ga0.47As/AlAs resonant-tunneling diodesmeasured by electro-optic sampling technique

To demonstrate picosecond-switching time for In_0.53Ga _0.47As/AlAs resonant-tunneling diodes (RTD's), we fabricated RTD's with various barrier widths and measured their switching times using electro-optic sampling technique specially arranged for RTD's with high current density. For an RTD having the barrier width of 1.4 nm with the peak current density of 4.5×10⁵ A/cm² and peak-to-valley ratio of 3.9, the switching time of 2.2 ps has been observed     

A GaAsMISFET using an MBE-grown CaF2 gate insulatorlayer

The CaF₂ layer and an undoped GaAs channel layer grown by molecular beam epitaxy (MBE) on a semi-insulating GaAs (100) substrate. The two layers are grown sequentially inside the same MBE chamber to form a clean CaF₂-GaAs interface. A self-aligned process using a WSi_x gate metal is used to fabricate the MISFET. A 1- μm gate-length FET exhibiting a transconductance of 64 mS/mm has been achieved     

A novel multiple-valued logic gate using resonant tunneling devices

We demonstrate a novel multiple-valued logic (MVL) gate using series-connected resonant tunneling devices. Logic operation is based on the control of the switching sequence of these devices through the modulation of their peak currents by the input signal. We obtain the literal function, one of fundamental MVL functions, by integrating three InGaAs-based resonant-tunneling diodes with two HEMT's on an InP substrate. The gate configuration is greatly simplified compared with a conventional literal gate employing CMOS circuits     

An exclusive-OR logic circuit based on controlled quenching ofseries-connected negative differential resistance devices

An exclusive-OR (XOR) logic circuit with clocked supply voltage based on the controlled quenching of series-connected negative differential resistance (NDR) devices is demonstrated. This controlled quenching process obeys a simple rule: the NDR device with the smallest peak current is always quenched first. In our present work, resonant-tunneling diodes provide the critical NDR feature, while FET's, which are integrated with RTD's in parallel, modulate the peak currents of NDR devices. The modulation of peak currents in different NDR devices directly controls the quenching sequence, and results in certain logic functions, one of which is XOR     

InGaAs resonant tunneling transistors using a coupled-quantum-wellbase with strained AlAs tunnel barriers

A bipolar-type resonant tunneling transistor is studied of which the base is identical to a coupled quantum well. On the basis of the InGaAs material system strained AlAs tunnel barriers and a graded InGaAlAs emitter are used. Molecular beam epitaxy growth conditions are studied, showing a specific influence of growth temperature and arsenic pressure. We find clear evidence for resonant tunneling: a saturation of the collector current and a maximum of the transconductance with increasing base-emitter bias in a three-terminal transistor structure. A corresponding effect in a phototransistor structure is found as a maximum of differential current gain with increasing incident light intensity. Room temperature and low temperature (80 K) high-frequency properties are determined and are used to estimate the resonant tunneling time     

Resonant-tunneling diode and HEMT logic circuits with multiplethresholds and multilevel output

By using resonant-tunneling diodes (RTDs) and high electron mobility transistors (HEMTs), we implement a new class of logic circuits that operate with multiple thresholds and multilevel output. The basic idea of the circuits is to synthesize transfer characteristics by key logic elements, namely, up and down literals. We first describe two fundamental logic circuits based on this idea: a ternary inverter and a literal gate. Then we present experimental results on these circuits fabricated by integrating InP-based RTDs and HEMTs. It is found that these circuits operate successfully with threshold voltages and output levels that have been predicted from individual device characteristics. Consequently, the validity of the basic idea behind the circuits presented here is proven. The device counts and the number of logic stages required for the present circuits are less than half those for conventional ones. A possible application is finally discussed