Shigeo Fujita

ZnO nanowires with high aspect ratios grown by metalorganic chemical vapor deposition using gold nanoparticles

ZnO nanowires with diameters ranging from 20 to 60 nm and lengths in the range 5–15 μm were synthesized by metalorganic chemical vapor deposition, assisted by colloidal gold nanoparticles with a diameter of 20 nm dispersed on SiO2∕Si substrates. The ZnO nanowires were found to have a high-internal quantum efficiency and negligibly weak deep-level emission, as evidenced by photoluminescence measurements. The clear observation of free-exciton and biexciton emission indicates that the ZnO nanowires prepared by this method are of high quality.

Spatial composition fluctuations in blue-luminescent ZnCdO semiconductor films grown by molecular beam epitaxy

Abstract The optical and structural properties of textured ZnCdO films that exibit a newly found distinct blue luminescence have been investigated. Microscopic compositional fluctuations of Cd, associated with hexagonal grain structures, were observed. Models for the blue-luminescence process are proposed.

Improvements of ZnO qualities grown by metal-organic vapor phase epitaxy using a molecular beam epitaxy grown ZnO layer as a substrate

Zinc oxide (ZnO) of high quality was homoepitaxially grown by metal-organic vapor phase epitaxy (MOVPE) on molecular beam epitaxy (MBE)-grown ZnO layers after the pretreatment of the underlying MBE-ZnO at 1000°C in N2 which resulted in an atomically flat surface. In photoluminescence at 15 K, the 3 meV line width of the emission from donor-bound-excitons (D0X) and the observation of the fourth phonon replica of the emission from free-excitons (EX) have demonstrated the high potential of MOVPE growth of ZnO toward optical applications.

Selective formation of ZnO nanodots on nanopatterned substrates by metalorganic chemical vapor deposition

Selective formation of ZnO nanodots was accomplished by metalorganic chemical vapor deposition on nanopatterned SiO2/Si substrates. Self-organized ZnO nanodots were selectively formed in nanopatterned lines of Si created by etching of SiO2 with focused ion beam (FIB), whereas any nanodots were hardly observed on the SiO2 surface in the vicinity of the FIB-sputtered Si areas. The mechanism of the selective formation of ZnO nanodots on FIB-nanopatterned lines is mainly attributed to the effective migration of Zn adatoms diffusing on the SiO2 surface into the Si lines followed by the nucleation at surface atomic steps and kinks created by Ga+ ion sputtering. Cathodoluminescence measurements confirmed that the emission originated from the selectively grown ZnO nanodots.Selective formation of ZnO nanodots was accomplished by metalorganic chemical vapor deposition on nanopatterned SiO2/Si substrates. Self-organized ZnO nanodots were selectively formed in nanopatterned lines of Si created by etching of SiO2 with focused ion beam (FIB), whereas any nanodots were hardly observed on the SiO2 surface in the vicinity of the FIB-sputtered Si areas. The mechanism of the selective formation of ZnO nanodots on FIB-nanopatterned lines is mainly attributed to the effective migration of Zn adatoms diffusing on the SiO2 surface into the Si lines followed by the nucleation at surface atomic steps and kinks created by Ga+ ion sputtering. Cathodoluminescence measurements confirmed that the emission originated from the selectively grown ZnO nanodots.

Self-Tailored One-Dimensional ZnO Nanodot Arrays Formed by Metalorganic Chemical Vapor Deposition

One-dimensional ZnO nanodot arrays have been realized by metalorganic chemical vapor deposition on SiO2 substrates patterned by focused ion beam (FIB). Especially for the lines with the depth of 5 nm and the length of 0.7, 1.3 or 1.7 µm, one, two or three nanodots, respectively, of fairly uniform size 6-nm height and 80-nm width are symmetrically accommodated in a line. These phenomena are translated as self-tailoring of ZnO nanodots, i.e., where the nanodots will be is predetermined before the growth and is arbitrarily controlled by the nanopatterns. This can be a promising technique to build nanostructure blocks for nanoscale device applications.

Focused Ion Beam Patterning for Fabrication of Periodical Two-Dimensional Zinc Oxide Nanodot Arrays

Widely well-aligned two-dimensional ZnO nanodot arrays (e.g., 40,000 nanodots of 130 nm diameter and 9 nm height over 150 ×150 µm2 with a period of 750 nm) have been fabricated by metalorganic chemical vapor deposition on SiO2/Si substrates patterned by focused ion beam (FIB). A low-magnification FIB patterning mode allowed the periodical nanopatterning of the substrates over a large area in a short time. Cathodoluminescence and photoluminescence were apparently observed from the ZnO nanodots.

Nonradiative recombination processes of carriers in InGaN/GaN probed by the microscopic transient lens spectroscopy

Temporally and spatially resolved observations of the nonradiative recombination (NR) processes of carriers in low dislocated GaN and InGaN/GaN were successfully obtained by using microscopic transient lens spectroscopy. The heat generations and conductivities of NR processes were detected by the signal intensities and the time profiles. We found that the thermal conductivities were not so different at the seed region (threading dislocation density (TDD)=1–2×109u2009cm−2) and the wing region (TDD=1–2×106u2009cm−2) of air-bridged lateral epitaxially grown GaN and InGaN/GaN, but the amount of heat generated at the wing regions was much smaller than that at the seed regions.