Satoshi Hiyamizu

A New Field-Effect Transistor with Selectively Doped GaAs/n-AlxGa1-xAs Heterojunctions

Studies of field-effect control of the high mobility electrons in MBE-grown selectively doped GaAs/n-AlxGa1-x As heterojunctions are described. Successful fabrication of a new field-effect transistor, called a high electron mobility transistor (HEMT), with extremely high-speed microwave capabilities is reported.

Pseudomorphic In/sub 0.52/Al/sub 0.48/As/In/sub 0.7/Ga/sub 0.3/As HEMTs with an ultrahigh f/sub T/ of 562 GHz

We fabricated decananometer-gate pseudomorphic In/sub 0.52/Al/sub 0.48/As/In/sub 0.7/Ga/sub 0.3/As high-electron mobility transistors (HEMTs) with a very short gate-channel distance. We obtained a cutoff frequency f/sub T/ of 562 GHz for a 25-nm-gate HEMT. This f/sub T/ is the highest value ever reported for any transistor. The ultrahigh f/sub T/ of our HEMT can be explained by an enhanced electron velocity under the gate, which was a result of reducing the gate-channel distance.

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.

Improved Electron Mobility Higher than 106 cm2/Vs in Selectively Doped GaAs/N-AlGaAs Heterostructures Grown by MBE

Electron mobility of quasi-two dimensional electron gas (2DEG) in selectively doped GaAs/N-AlxGa1-xAs (x=0.3) heterostructures grown by MBE was investigated as a function of thickness of an undoped AlxGa1-xAs spacer-layer (0–200 A) introduced between a Si-doped AlGaAs layer and an undoped GaAs layer, at 77 K and 5 K. Mobility of 2DEG as high as 2,120,000 cm2/Vs at 5 K was achieved with a spacer-layer thickness of 200 A. This electron mobility is higher than any observed so far in semiconductor materials.

547-GHz f/sub t/ In/sub 0.7/Ga/sub 0.3/As-In/sub 0.52/Al/sub 0.48/As HEMTs with reduced source and drain resistance

We fabricated 30-nm gate pseudomorphic channel In/sub 0.7/Ga/sub 0.3/As-In/sub 0.52/Al/sub 0.48/As high electron mobility transistors (HEMTs) with reduced source and drain parasitic resistances. A multilayer cap structure consisting of Si highly doped n/sup +/-InGaAs and n/sup +/-InP layers was used to reduce these resistances while enabling reproducible 30-nm gate process. The HEMTs also had a laterally scaled gate-recess that effectively enhanced electron velocity, and an adequately long gate-channel distance of 12nm to suppress gate leakage current. The transconductance (g/sub m/) reached 1.5 S/mm, and the off-state breakdown voltage (BV/sub gd/) defined at a gate current of -1 mA/mm was -3.0 V. An extremely high current gain cutoff frequency (f/sub t/) of 547 GHz and a simultaneous maximum oscillation frequency (f/sub max/) of 400 GHz were achieved: the best performance yet reported for any transistor.

High Electron Mobility Transistor Logic

A high electron mobility transistor (HEMT) logic is described. Ring oscillators with enhancement-mode switching and depletion-mode load HEMTs with a 1.7 µm-gate length have been fabricated to assess logic performance capability. Switching delays down to 56.5 ps at room temperature and down to 17.1 ps at liquid nitrogen temperature have been obtained. The switching delay of 17.1 ps is the lowest of all the semiconductor logic technologies reported thus far.

A pseudomorphic In0.53Ga0.47As/AlAs resonant tunneling barrier with a peak-to-valley current ratio of 14 at room temperature

We have studied the effect of barrier height on the negative differential resistance characteristics of In0.53Ga0.47As-based resonant tunneling barriers (RTBs), including In0.53Ga0.47As/(In0.52Al0.48As)x(In0.53Ga0.47As)1-x RTBs, lattice-matched to an InP substrate, and In0.53Ga0.47As/AlAs pseudomorphic RTBs also grown on InP substrates. A peak-to-valley current ratio of 14 (300 K) and 35 (77 K) with a high peak-current density of 2.3×104A/cm2 was achieved for a resonant tunneling barrier structure of In0.53Ga0.47As (15 atomic layers)/AlAs (9 atomic layers).

Ultra-short 25-nm-gate lattice-matched InAlAs/InGaAs HEMTs within the range of 400 GHz cutoff frequency

We have succeeded in fabricating ultra-short 25-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates. The two-step-recessed gate technology and low temperature processing at below 300/spl deg/C allowed the fabrication of such ultra-short gates. DC measurements showed that the 25-nm-gate HEMT had good pinchoff behavior. We obtained a cutoff frequency f/sub T/ of 396 GHz, within the range of 400 GHz f/sub T/, for the 25-nm-gate HEMT. This f/sub T/ is the highest value get reported for any type of transistor, and the gate length of 25 nm is the shortest value ever reported for any compound semiconductor transistor that exhibits device operation.

Conduction band edge discontinuity of In0.52Ga0.48As/In0.52(Ga1−xAlx)0.48As (0≤x≤1) heterostructures

In0.52Ga0.48As/In0.52(Ga1-xAlx)0.48As/In0.52Ga0.48As potential barrier structures (x=0.25, 0.5, 0.75, 1), lattice-matched to InP, were grown by MBE using a pulsed molecular beam method. The conduction band edge discontinuity, ΔEc(x) between In0.52Ga0.48As and In0.52(Ga1-xAlx)0.48As, was obtained for the first time by measuring the current-voltage characteristics through the barrier structure as a function of temperature in the range of 77–300 K. It was confirmed that the conduction band edge discontinuity varies linearly with Al composition, x, (ΔEc(x)=0.53x(eV) for 0x1) and is proportional to the band gap difference, ΔEg(x), (ΔEc(x)=0.72ΔEg(x)(eV) for 0x1).

Ultrahigh-speed pseudomorphic InGaAs/InAlAs HEMTs with 400-GHz cutoff frequency

An excellent cutoff frequency (f/sub t/) as high as 400 GHz was successfully realized in 45-nm-gate pseudomorphic InGaAs/InAlAs high electron mobility transistors (HEMTs). An additional vertical gate-recess suppressed short-channel effects, while keeping good pinchoff characteristics. Gate length (L/sub g/) dependence of electron transit time (/spl tau//sub transit/) implied an increased saturation velocity (/spl upsi//sub s/) of 3.6/spl times/10/sup 7/ cm/s in the developed pseudomorphic HEMTs. This f/sub t/ is the highest value ever reported for any transistors to date.