Daihei Hippo

Visible Electroluminescence from Spherical-Shaped Silicon Nanocrystals

We fabricated light emitting diodes (LEDs) using spherically shaped nanocrystalline silicon (nc-Si), which was formed through very high frequency (VHF; 144 MHz) plasma decomposition of SiH4. In addition, we successfully reduced the roughness of the surface and part of the voids separating the dots by finding the adequate annealing conditions. Red electroluminescence was also observed at 12 V with the naked eye at room temperature under forward bias condition. It is suggested that the origin of the electroluminescence (EL) from Si nanocrystals is due to recombination centers in Si nanocrystals by the comparison of EL and photoluminescence spectra.

Characteristics of thermally induced acoustic emission from nanoporous silicon device under full digital operation

The resonance-free frequency response of the thermo-acoustic emission is demonstrated under a full digital drive. The device is composed of a thin-film heater electrode, a nano-porous silicon layer, and a single-crystalline silicon wafer. When sequential electrical pulse trains converted by the density modulation of an analog signal are introduced into the heater electrode, a significant sound pressure is reproduced with a sufficiently low distortion. The characteristic output behaviour in the audible ultrasonic band is clarified in either open- or closed-space. The advantageous features of thermally induced sound emission and its underlying physics have been made clear.

Formation Mechanism of 100 nm-Scale Periodic-Structures in Silicon Using Magnetic-Field-Assisted Anodization

We demonstrate highly directional etching in silicon 100 nm in diameter with an aspect ratio of 160 with no spiking on the pore walls using magnetic-field-assisted anodization. The relationship between the surface geometry of a silicon electrode and its highly directional etching properties have been investigated. Specifically, we show that the pore shape and pore wall orientation are not determined by the surface pattern but by the etching mechanisms specific to the magnetic-field-assisted anodization. These etching mechanisms enable highly directional and high aspect ratio etching at diameters below 100 nm in scale.

New Design Concept and Fabrication Process for Three-Dimensional Silicon Photonic Crystal Structures

We propose a new design concept and a fabrication process for three-dimensional (3D) silicon photonic crystals on a 100 nm scale that does not require any alignment processes. The elemental technique used in this process is two directional electrochemical etching processes at a particular magnetic field. First, we have performed photonic band calculation and estimated device parameters to obtain the maximum photonic band gap in the visible range centered at around 800 nm. Next, we have experimentally observed the formation of a two-dimensional periodic pore with a diameter of 80 nm and an aspect ratio above 80 on an n+ (100) silicon substrate. Finally, we have fabricated 3D microstructures by two directional etching processes. A clear directionality for the pore formation was observed in two directions, showing the possibility of projecting the patterns formed on the slope to the side of the wafer. These fundamental etching processes can be applied to the fabrication of 3D photonic crystals in the visible range without any alignment processes.

A new design of nanocrystalline silicon optical devices based on 3-dimensional photonic crystal structures

We propose a new design of nanocrystalline silicon optical devices which are based on control of electromagnetic fields, electronic states, as well as the phonon dispersion of size-controlled silicon quantum dots.

Laser-induced photoluminescence enhancement in a room-temperature emitting SiGe-based alloy quantum well

An enhancement of photoluminescence (PL) intensity was observed at room temperature in a SiGe/Si quantum well under continuous laser illumination. The laser-induced PL enhancement was found to be an irreversible process characterized by a time constant which decreases with increasing excitation power density. A modified defect reduction model based on recombination-enhanced defect reaction is invoked to interpret the PL enhancement in terms of an improvement in the crystal quality of quantum well layers induced by laser radiation.

Optical Properties of Silicon Three-Dimensional Photonic Crystal Fabricated by Self-Aligned Two-Directional Electrochemical Etching Method

We have developed a new fabrication process of three-dimensional photonic crystal (3DPC) structures using the self-aligned two-directional electrochemical etching method. We performed optical measurements to clarify the properties of the fabricated 3DPC structures and observed a decrease in the reflectance. We also observed for silicon nanocrystals deposited on the 3DPC structures that the photoluminescence (PL) intensity was increased and the PL decay time was reduced at the same wavelength centered around 750 mn. These experimental results are attributed to the cavity modes formed at defects in the 3DPC structures.

Light emission from size reduced nanocrystal silicon quantum dots

We performed HF treatment to silicon quantum dots with diameter of 8 nm plusmn 1 nm fabricated by VHF plasma decomposition process. We observed PL wavelength shift from 750 nm to 620 nm for 8 nm to 2.5 nm diameter nc-Si dots.

Visible electroluminescence from size-controlled silicon quantum dots

We studied visible EL from size-controlled silicon quantum dots with diameter of 8 nmplusmn1 nm fabricated by VHF plasma decomposition process. We observed EL from nc-Si quantum dots with applied voltage above 12 V.

Fabrication of silicon 3D photonic crystal structures in 100nm scale using double directional etchings method

We have reported periodic pore formation with diameter in 80 nm and aspect ratio above 250 on N+(100) silicon substrate and demonstrated the fabrication of silicon 3-dimensional microstructures by applying double directional etchings method.