H. Ohnishi

Self‐consistent analysis of resonant tunneling current

We investigated the current‐voltage characteristics of the double barrier, resonant tunneling structure, using a self‐consistent method. We note the significance of the effects of band bending and buildup of space charge in the quantum well. For the peak current, our calculated results agree with the measured results very well. However, the measured valley current is much greater than the calculated values.

Excellent Negative Differential Resistance of InAlAs/InGaAs Resonant Tunneling Barrier Structures Grown by MBE

Light electron effective mass was found to be a very important parameter for improving the negative differential resistance (NDR) of a resonant tunneling barrier (RTB) structure. An InAlAs (41 A)/InGaAs (61.5 A)/InAlAs (41 A) RTB structure, lattice-matched to Ink, has been grown for the first time by MBE and dramatically improved NDR has been achieved. Peak current density as high as 2.2×104 A/cm2 with an excellent peak-to-valley current ratio of 11.7 was obtained at 77 K, which is the best data ever reported so far for any RTB structures.

RESONANT-TUNNELING HOT ELECTRON TRANSISTOR (RHET)

Abstract This paper reviews our current activities in hot electron transistors, and then describes recent advances in the RHET technology using InGaAs-based materials. The RHETs emitter common current gain is typically 10 to 17, with a maximum of 25, which is about four times greater than that of a GaAs-based RHET. The collector current peak-to-valley ratio reaches 19.3, with a maximum of 21.7, eight times that of the GaAs-based RHET. These are followed by theoretical and experimental analyses of the RHETs DC performance. It is found that theoretical and experimental results do not agree for the GaAs-based RHET but agree well for the InGaAs-based RHET.

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.

Quantum Well Width Dependence of Negative Differential Resistance of In0.52Al0.48As/In0.53Ga0.47As Resonant Tunneling Barriers Grown by MBE

The effect of quantum well width on the negative differential resistance (NDR) at 77 K of an InAlAs/InGaAs resonant tunneling barrier structure, lattice-matched to InP substrates and grown by MBE, was studied. The best NDR characteristics ever reported (peak-to-valley ratio of 11.4 with peak current density of 5.5×104 A/cm2) have been achieved for a resonant tunneling barrier diode with a thin quantum well width of 44 A. A reduction of electron effective mass in the InAlAs barrier layer was also observed.

A full adder using resonant-tunneling hot electron transistors (RHETs)

Full adders are demonstrated using InGaAs-In(AlGa)As RHETs. The RHETs emitter and base electrodes were self-aligned using a SiO/sub 2/ sidewall and angled beam ion milling. The common-base current gain was about 0.9 and the emitter current peak-to-valley ratio was 10. The RHET full adder was constructed using a three-input exclusive-OR logic gate and a three-input majority logic gate. The authors confirmed normal operation of the full adder at 77 K. Only seven RHETs were needed for the full adder, about one-quarter of bipolar transistors that would have been required. >

3.5 V, 1 W high efficiency AlGaAs/GaAs HBTs with collector launcher structure

AlGaAs/GaAs HBTs with collector launcher structure are developed for the low operation voltage power amplifier. We discuss the relationship between the HBT collector structure and its microwave power performance, demonstrating that the launcher structure suppresses the Kirk effect near the saturation region and increases the current handling capability. A fabricated HBT, which has an emitter size of 2 /spl mu/m/spl times/20 /spl mu/m/spl times/32 fingers, exhibits a power added efficiency, /spl eta/add, of 70% with an output power, Pout, of 30 dBm and a power gain, Ga, of 15.7 dB at a supply voltage of 3.5 V and a frequency of 900 MHz. At 2.5 V, Pout is 26.5 dBm, /spl eta/add is 70% and Ga is 14.7 dB. These results demonstrate that HBTs with a collector launcher structure are appropriate for power applications, especially at low voltage operation.<<ETX>>

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. >

A 3-ns GaAs 4K &#215; 1-bit static RAM

A 3-ns 700-mW GaAs 4K × 1-bit static RAM has been developed using tungsten-silicide-gate self-aligned technology with a minimum design rule of 1.5 µm. A GaAs 1K × 1-bit static RAM, developed using the same technology, affords 1.0-ns minimum address access time and 300-mW power dissipation.

Characterization of GaAs/AlGaAs hot electron transistors using magnetic field effects on launched-electron transport

Magnetic field effects on launched-electron transport in GaAs/AlGaAs hot electron transistors (HETs) were investigated. Using magnetic field effects, the smallest base transit time is estimated to be around 0.1 ps. Electron velocity reaches 1 × 108cm/s. These results are the first evidence of quasi-ballistic transport of electrons.