T. Futatsugi

Microstructure and electrical properties of Sn nanocrystals in thin, thermally grown SiO2 layers formed via low energy ion implantation

We have developed a simple technique for fabricating Sn nanocrystals in thin thermally grown SiO2 layers using low energy ion implantation followed by thermal annealing. The formed Sn nanocrystals have excellent size and depth uniformity. Their average diameter is 4.2 nm with a standard deviation of 1.0 nm. Our experimental results clearly reveal that a stable depth of Sn exists in the SiO2 layer at about 2 nm from the SiO2/Si interface. Most of the Sn nanocrystals reside near this stable depth. The I–V characteristics of the diode structure show a clear Coulomb blockade region of 0.12 V and a Coulomb staircase at 4.2 K. A Coulomb blockade region around 0 V was observed until reaching a temperature of 77 K. The features of these nanocrystals will open up new possibilities for the creation of novel devices.

Self-assembled structures of closely stacked InAs islands grown on GaAs by molecular beam epitaxy

Abstract Closely stacked Stranski-Krastanow (SK) growth islands were investigated. InAs islands of nominal 1.8 monolayer thickness were grown periodically with GaAs intermediate layers of less than 3 nm by molecular beam epitaxy. Reflection high-energy electron diffraction and atomic force microscopy revealed that SK growth islands were formed even with stacked intervals of 2 nm, but the upper island size expanded slightly as the number of stacked layers increased. Transmission electron microscopy revealed that upper islands grew closely just on the lower islands aligning vertically on the first layer islands. Drastic decrease in photoluminescence full-width at half-maximum less than 30 meV was obtained from this structure.

Si single electron tunneling transistor with nanoscale floating dot stacked on a Coulomb island by self-aligned process

We fabricated a Si single electron tunneling transistor which has a nanoscale floating dot gate stacked on a Coulomb island by a self-aligned process. This device exhibits drain current (Id) oscillations due to the Coulomb blockade effect and quantized threshold voltage (Vth) shifts resulting from a single electron tunneling from the channel to the floating dot gate. The high on/off current ratio of the Id oscillation combined with the quantized Vth shifts leads to the possibility of developing ultralow power consumption memory.

Formation of Sn nanocrystals in thin SiO2 film using low-energy ion implantation

This letter reports on a simple technique for fabricating Sn nanocrystals in thin SiO2 film using low-energy ion implantation followed by thermal annealing. These Sn nanocrystals have excellent size uniformity and position controllability. Their average diameter is 4.8 nm with a standard deviation of 1.0 nm. Most of the Sn nanocrystals reside at the same depth. The lateral edge-to-edge spacing between neighboring Sn nanocrystals is fairly constant: about 3 nm. A narrow as-implanted ion distribution profile and the effect of the SiO2–Si interface are considered to contribute to the size uniformity and position controllability. The features of these nanocrystals will open up new possibilities for novel devices.

Coulomb blockade in Sb nanocrystals formed in thin, thermally grown SiO2 layers by low-energy ion implantation

Sb nanocrystals were formed in thin, thermally grown SiO2 layers using low-energy ion implantation followed by thermal annealing. These Sb nanocrystals have good size and position uniformity. Both the narrow as-implanted profile and the compressive strain that exists near the SiO2/Si interface supposedly contribute to the uniformity. The I–V characteristics of the diode structure show a Coulomb blockade region around 0 V and a Coulomb staircase at 4.2 K. The Coulomb blockade region was observed up to a temperature of 100 K. The technique offers the possibility of developing practical Si-based single-electron devices.

Quantum Dot Infrared Photodetector Using Modulation Doped InAs Self-Assembled Quantum Dots

We report the quantum dot infrared photodetector using the modulation doped InAs self-assembled quantum dots. By modulation doping, it is possible to remove the effect of the dopants on the energy level in InAs dots and to attribute clearly the infrared photocurrent to the carrier excitation in InAs dots. The infrared photocurrent in the detector was clearly observed up to 30 K. The peak energy and the polarization dependence of the infrared photocurrent are comparable to the infrared electron excitation from the ground state in InAs dots to the conduction band edge of GaAs barriers.

V/sub th/ fluctuation induced by statistical variation of pocket dopant profile

This paper studies effect of pocket (halo) profile on V/sub th/ fluctuation due to statistical dopant variation by measurement and simulation. A pocket profile significantly enhances V/sub th/ fluctuation by a factor of >15% at worst even if the implantation process variations would be negligible. This is because pocket dopants shrink the area which controls V/sub th/.

Narrow photoluminescence line width of closely stacked InAs self-assembled quantum dot structures

We report an effect of interval layer thickness in stacked InAs self-assembled quantum dot (QD) structures on photoluminescecnce (PL) characteristics focusing on thicknesses less than 3 nm. A drastic decrease in PL line width as narrow as 21 meV at 4.2 K was obtained with 2-nm interval layers. PL measurements show that the stacked structure forms an equivalent single QD structure which vertical size is extended effectively more than that of single layer QD. This attributes to the decrease of PL line width governed by the fluctuation mainly in the vertical direction. PL from higher order quantized states up to the 4th state are also clearly observed.

ELECTRON TRANSPORT PROPERTIES THROUGH INAS SELF-ASSEMBLED QUANTUM DOTS IN MODULATION DOPED STRUCTURES

We report electron transport properties through InAs self-assembled quantum dots in a modulation-doped structure with split gates. We observed drain current modulation with respect to gate voltage due to electron transport through the quantum level of InAs dots. The energy gaps estimated from the temperature dependence study of valley current and the voltage difference between the drain current peaks were consistent with each other and as large as 14 meV. The energy gaps can be explained by the charging energy of the InAs dots.

Room temperature operation of Si single-electron memory with self-aligned floating dot gate

Reports on a new Si single-electron memory device comprised of a narrow channel field effect transistor (FET) having an ultra-small selfaligned floating dot gate and its ability to exhibit clear, single-electron memory effects at room temperature.