Yukari Ishikawa

SiGe-on-insulator substrate using SiGe alloy grown Si(001)

Low-energy oxygen ion (25 keV O+) implantation was performed on a pseudomorphic Si1−xGex/Si(001) of uniform composition in an attempt to create a SiGe-on-insulator (SiGe-OI) substrate using the separation-by-implanted-oxygen technique. Choosing a small Ge composition (<0.3) was found to be essential to achieving a SiGe-OI geometry of structural integrity.

SiGe-based semiconductor-on-insulator substrate created by low-energy separation-by-implanted-oxygen

SiGe-based semiconductor-on-insulator (SOI) substrates have been successfully created by the separation-by-implanted-oxygen technique. Low-energy oxygen ion implantation was performed at 25 kV on a strain-relieved Si0.82Ge0.18 virtual substrate grown on Si(001). A good SOI geometry with a 25-nm top SiGe layer was obtained over a dose window of 2–2.5×1017 cm−2, and a flat SiGe surface and sharp SiGe/SiO2 interfaces were achieved at a low substrate temperature of 550°C. Compositional analysis shows that the top SiGe layer nearly conserves the same composition as the underlying alloy substrate.

Color control of white photoluminescence from carbon-incorporated silicon oxide

Color control of the white photoluminescence (PL) from carbon-incorporated silicon oxide is demonstrated. The carbon-incorporated silicon oxide was fabricated by carbonization of porous silicon in acetylene flow (at 650 and 850 °C) followed by wet oxidation (at 650 and 800 °C). It was shown that PL color can be controlled in the range of blue-white and yellow-white by selecting the porosity of starting porous silicon as well as the carbonization and oxidation temperatures. Low-temperature oxidation resulted in bluish light emission in lower porosity series, while high-temperature oxidation promoted yellow-white light emission. The maximal integral intensity of PL was observed after oxidation at 800 °C. It was shown that white PL from carbon-incorporated silicon oxide has blue and yellow-white PL bands originating from different light-emitting centers. The origin of blue PL is attributed to defects in silicon dioxide. Some trap levels at the interface of the carbon clusters and silicon oxide are suggested ...

Growth of Aluminum Nitride Films on Silicon by Electron-Cyclotron-Resonance-Assisted Molecular Beam Epitaxy

Aluminum nitride thin films have been prepared on silicon substrates by electron-cyclotron-resonance plasma-assisted molecular beam epitaxy (ECR-MBE). Epitaxial AlN films have been obtained by Al evaporation and 250 eV nitrogen ion irradiation on a clean Si surface at 700°C. AlN films with two kinds of crystal orientations were grown epitaxially on Si(111). The dominant one is AlN (0001)//Si(111); AlN[010]//Si[11] and the another one is AlN(010)//Si(111); AlN[0001]//Si[11].

Epitaxy‐ready Si/SiO2 Bragg reflectors by multiple separation‐by‐implanted‐oxygen

A Si substrate purposely grown for Si‐based optoelectronic applications is described in this letter. The structure contains a built‐in Si/SiO2 Bragg reflector which is prepared by multiple separation‐by‐implanted‐oxygen technique, where in situ low energy oxygen ion implantation is performed on molecular beam deposited Si to create alternating Si/SiO2 epitaxial bilayers. The quality of the top Si layer was confirmed to be epitaxy‐ready after cross‐sectional transmission electron microscopy. Maximum reflectance at near normal incidence was over 90% for bilayer periods of 4 to 5.

Preparation of Thin Silicon-on-Insulator Films by Low-Energy Oxygen Ion Implantation

Silicon-on-insulator (SOI) structures have been formed by oxygen implantation with the ion energy of 15-30 keV in silicon wafers. The ion implantation conditions which produce the SOI structure have been investigated both by calculation and experiments. As-implanted layers were analyzed by Auger electron spectroscopy and cross-sectional transmission electron microscopy. The thicknesses of the SOI layer and the buried amorphous SiOx layer are 48 and 61 nm, respectively, under the conditions at the O+ ion energy of 25 keV, with the dose of 2×1017 ion/cm2, and at about 450°C. The SOI layers are homogeneous and have sharp Si/SiOx interfaces.

Fabrication of highly oriented Si:SiO2 nanoparticles using low energy oxygen ion implantation during Si molecular beam epitaxy

A novel technique is developed for fabricating highly oriented Si nanoparticles (SNP) embedded in SiO2 using multiple low energy oxygen ion implantation during Si molecular beam epitaxy. The SNPs are of nearly isotropic but faceted morphologies with almost perfect crystallinity as revealed by transmission electron microscopy. The preferred axis of SNP cores is found to be aligned to [100] due to epitaxy on a Si(100) substrate, reflecting the highly oriented character of SNPs. Visible luminescence from SNPs with dimensions approaching the quantum confinement regime is observed at room temperature.

Transmission Electron Microscopy Analysis of a Threading Dislocation with c+a Burgers Vector in 4H-SiC

A threading dislocation (TD) in 4H-SiC, which was interpreted as a right-handed threading screw dislocation (TSD) by synchrotron monochromatic-beam X-ray topography (SMBXT) and molten KOH etching with Na2O2 additive (KN etching), was characterized by large-angle convergent-beam electron diffraction (LACBED) and weak-beam dark-field methods. It was found that this TD was a so-called c+a dislocation with Burgers vector of b=[0001]+(1/3)[2110], which is often misinterpreted as TSD (c-dislocation) by SMBXT and KN etching. The rotation direction of the screw component within the c+a TD determined by LACBED agreed with the SMBXT observation.

Strong white photoluminescence from carbon-incorporated silicon oxide fabricated by preferential oxidation of silicon in nano-structured Si:C layer

A new approach to development of light-emitting SiO2:C layers on Si wafer is demonstrated. Carbon-incorporated silicon oxide was fabricated by three-step procedure: (1) formation of the porous silicon (por-Si) layer by ordinary anodization in HF:ethanol solution; (2) carbonization at 1000 °C in acetylene flow (formation of por-Si:C layer); (3) oxidation in the flow of moisturized argon at 800 °C (formation of SiO2:C layer). Resulting SiO2:C layer exhibited very strong and stable white photoluminescence at room temperature. It is shown that high reactivity of water vapor with nano-crystalline silicon and inertness with amorphous carbon play a key role in the formation of light-emitting SiO2:C layer.

Effects of Surface Oxides of SiC on Carbon Nanotube Formation by Surface Decomposition

The effects of chemical treatment on carbon nanotube (CNT) formation by surface decomposition of 6H–SiC were investigated. In the case of 6H–SiC cleaned with CH2Cl2, CNTs were formed only on the C-(0001) face. On the other hand, in the case of 6H–SiC etched with HF solution, CNTs were formed on both C-(0001) and Si-(0001) faces. X-ray photoelectron spectroscopy (XPS) analysis detected SiOxCy on the C-(0001) face, and SiO2 and SiOvCw on the Si-(0001) face of SiC cleaned with CH2Cl2. The existence of SiO2 on the SiC surface prevented CNT formation. The length of CNTs on the Si-(0001) face was about 65% of that on the C-(0001) face. The length of CNTs on the C-(0001) face was not affected by chemical treatment. The difference of CNT length between the C and the Si faces originated from the anisotropy of thermal oxidation.