Kenichi Imamura

A New Functional, Resonant-Tunneling Hot Electron Transistor (RHET)

Abstract-A new functional, resonant-tunneling hot electron transistor (RHET) is demonstrated in which electrons are injected from emitter to base by resonant-tunneling through a quantum well, and are near-ballistically transferred to a collector. The main feature of this device is a peaked collector-current characteristic with respect to the base-emitter voltage. This enables us to build a frequency multiplier or an Exclusive-NOR gate using only one transistor.

New Optical Memory Structure Using Self-Assembled InAs Quantum Dots

We propose a new optical memory structure using self-assembled InAs quantum dots (QDs) for possible applications to wavelength-domain-multiplication memory, which should lead to increase memory density. Data stored in this memory structure can be read using photocurrent and then erased electrically. In a preliminary study, we confirmed the memory effect of photocurrent caused by the InAs QDs for the first time. A retention time of 0.48 ms for the memory was obtained at 300 K.

Stacked InAs Self-Assembled Quantum Dots on (001) GaAs Grown by Molecular Beam Epitaxy

We report stacked InAs self-assembled quantum dot (QD) structures separated by GaAs interval layers grown by molecular beam epitaxy on a (001) GaAs substrate. The InAs QDs were vertically aligned up to the 9th layer. Strain in the interval layer induced by the lower QD strongly influences the upper QD alignment. A large defect due to lateral In segregation was observed with multiple stacked InAs self-assembled QD structures, which suppresses further vertical alignment of QDs in the upper region and decreases photoluminescence intensity drastically. Optical memory effect of InAs QDs buried in Schottky barrier diode was observed with memory retention time of 0.48 ms for the first time.

Tunneling Hot Electron Transistor Using GaAs/AlGaAs Heterojunctions

The first tunneling hot electron transistor (HET) using semiconductor heterojunctions has been achieved. This device uses GaAs/AlGaAs heterojunctions grown by molecular beam epitaxy and sophisticated process technology. Transfer efficiency for hot electrons through 100 nm thick n-GaAs was measured as 0.28.

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 functional devices for advanced electronics

Abstract Recent research in semiconductor device technology seems to be focused on reducing the cost and power dissipation of traditional Si CMOS integrated circuits, rather than developing new and advanced semiconductor devices. We believe however, that devices enter the nanometer-scale regime in the next century, where quantum mechanical effects play an important role in the devices function; therefore, it is important to continue basic research into the physics and technology of nanometer scale structures and device applications in order to cultivate “nanoelectronics”. This paper reviews our research activities on quantum functional devices and discusses our future research direction.

A resonant-tunneling bipolar transistor (RBT)―a new functional device with high current gain

A resonant-tunneling bipolar transistor (RBT) has been proposed and demonstrated. This is a AlGaAs/GaAs hetero-junction bipolar transistor using a AlAs/GaAs/ AlAs quantum well resonator as a minority carrier injector. The RBT exhibits a collector-current peak with respect to the base-emitter voltage, and therefore a negative transconductance, due to resonant-tunneling of electrons. The common-emitter current gain reaches 20 at 77 K. We also observed a base-current peak due to resonant-tunneling of holes.

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. >

A WSi/TiN/Au Gate Self-Aligned GaAs MESFET with Selectively Grown n+-Layer using MOCVD

A WSi/TiN/Au gate self-aligned GaAs MESFET was formed using MOCVD. The WSi/TiN/Au gate acts as a selective growth mask for the n+-layer. This new process is demonstrated to be effective for reducing the gate resistance and source resistance of FETs simultaneously. The gate resistance, Rg, was 3.4 Ω (Lg=1.3 um, Wg=30 um) and was reduced one tenth compared to that of the WSi gate. A high-speed MSI and high performance microwave device can be obtained by using the WSi/TiN/Au gate self-aligned GaAs MESFETs.