Tsuguo Inata

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.

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).

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).

Direct observation of picosecond spin relaxation of excitons in GaAs/AlGaAs quantum wells using spin-dependent optical nonlinearity

We have directly observed spin relaxation of excitons in the picosecond region using time‐resolved polarization absorption measurements. With the help of spin‐dependent optical nonlinearity of excitonic absorption, we obtained a fast decay of spin‐up carriers and a fast accumulation of spin‐down carriers with a spin relaxation time of 32 ps for a GaAs/Al0.51Ga0.49As multiple quantum well at room temperature with a time resolution of 1 ps.

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.

MBE growth of InGaAs-InGaAlAs heterostructures for applications to high-speed devices

Abstract InGaAs-In(Ga 1− x Al x )As (0⩽ x ⩽1) multilayer heterostructures, lattice-matched to InP, were grown with good reproducibility by a new MBE technique using a pulsed molecular beam method. Electronic properties of the InGaAs-In(Ga 1− x Al x )As heterostructures, including selectively doped InGaAs/N-InAlAs heterostructures and InGaAs-InAlAs resonant tunneling barrier structures, are described, and their high potential for applications to high-speed devices is discussed.

Near-1.3-μm high-intensity photoluminescence at room temperature by InAs/GaAs multi-coupled quantum dots

We propose a new quantum dot system called multi-coupled quantum dots. In this system, since quantum dots couple with adjacent dots, the photoexcited carriers tunnel into the larger quantum dots which have lower energy states. This energy relaxation results in narrower and stronger photoluminescence than with conventional quantum dots. InAs/GaAs self-organized multi-coupled quantum dots show strong photoluminescence near 1.3 µ m at room temperature, whose intensity is as large as in the well-known highly efficient InGaAs/GaAs quantum wells.

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.

Current‐voltage characteristics of In0.53Ga0.47As/In0.52Al0.48As resonant tunneling barrier structures grown by molecular beam epitaxy

Well width dependence and temperature dependence of negative differential resistance characteristics of InGaAs/InAlAs resonant tunneling barrier diodes were investigated. Peak current density was almost independent of temperature, while the valley current density increased with increasing temperature above 100 K. At room temperature, a peak‐to‐valley current ratio of 5.5 with a peak current density of 4.8×104 A/cm2 was obtained by reducing the quantum well width to a narrow 32.2 A. This is the largest peak‐to‐valley current ratio ever reported for resonant tunneling barrier diodes at room temperature.

Longitudinal-optical-phonon assisted tunneling in tunneling bi-quantum well structures

We discuss the electron tunneling time observed in a new AlGaAs/GaAs superlattice structure, the tunneling bi‐quantum well (TBQ). To calculate the nonresonant tunneling time, we made experiments on resonant tunneling to confirm that the 60% rule of conduction‐band discontinuity accurately evaluates the free tunneling probability of electrons. We found that the observed recovery time agrees quite well with the calculated longitudinal optical phonon emission tunneling time for thin (≤ 10 monolayers) barriers.