Noriko Nitta

Formation of cellular defect structure on GaSb ion-implanted at low temperature

Formation of the anomalous cellular structure in (100) GaSb with Sn ion-implantation at a low temperature is investigated by cross-sectional scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. A fine structure consisting of many cells was formed on GaSb surface implanted by 60 keV Sn. The cell diameter and the thickness of the walls partitioning the cells were about 50 and 10 nm, respectively, which are almost constant in the range of the ion dose 4.0×1014–8.9×1014 ions/cm2. The depth of the cells increased linearly with increasing ion dose, from 100 nm in the sample implanted with a dose of 4.0×1014 ions/cm2 to 220 nm in that implanted with a dose of 8.9×1014 ions/cm2. From the experimental results, it is concluded that the development of the cellular structure originates in formation of the voids. An improved defect formation mechanism based on movement of the implantation-induced point defects is discussed.

Novel nano-fabrication technique utilizing ion beam

Abstract Novel nano-fabrication technique is proposed on the basis of knowledge of anomalous behavior in ion-implanted GaSb and InSb at low temperatures. An initial array of hollows or voids is fabricated precisely on or under the substrate surface by focussed ion beam (FIB) and the structure is developed self-organizationally utilizing movement of point defects induced by ion implantation at relatively low temperatures. The precision in this technique is dominated mainly by extension of irradiation damage. Structure of 20-nm scale is fabricated at present technical level and that of 5-nm scale will be realized by improving the accuracy of FIB.

Analysis of a wafer bonded Ge/Si heterojunction by transmission electron microscopy

A wafer-bonded Ge∕Si heterojunction was observed using transmission electron microscopy to analyze its crystallographic properties and to reveal atomic profiles at the interface by energy dispersive x-ray spectroscopy. There was a 2nm thick transition layer at the heterojunction, where an aligned lattice image from Si to Ge together with a disordered lattice image could be observed. In the Si layer close to the interface, islandlike modified regions were observed to exist, where a large amount of Ge was detected. Oxygen was also detected accumulated at the interface.

Beam flux dependence of ion-irradiation-induced porous structures in III–V compound semiconductors

Beam flux dependence of ion-irradiation-induced porous structures in GaSb and InSb were studied by focused ion beam. The void and elevation structure were formed after irradiation. The average diameter of the void was approximately 42 nm in the sample irradiated to a flux of 4×1017 ions/m2s and 61 nm in the sample irradiated to a flux of 30×1017 ions/m2s in GaSb in a total fluence of 20×1018 ions/m2. It is considered that many vacancies are immediately induced in the sample of high-flux irradiation. Therefore, the diameter of the void in high-flux irradiation is larger than it is in low-flux irradiation.

Photoluminescence, morphology, and structure of hydrothermal ZnO implanted at room temperature with 60 keV Sn+ ions

Hydrothermal ZnO wafers implanted at room temperature with 60 keV Sn+ ions are examined by means of photoluminescence (PL), atomic force spectroscopy (AFM), and X-ray diffractometry techniques. The PL intensity significantly decreases in the wafers implanted to doses of 4.1 × 1013 ions/cm2 and higher. The AFM measurements indicate that surface roughness variation is not the cause of the significant decrease in PL intensity. Furthermore, the PL deep level (DL) band peak blueshifts after illuminating the implanted samples with the He-Cd laser 325 nm line; meanwhile, the DL band intensity first increases and then decreases with illumination time. These abnormal behaviors of the DL band are discussed.

One-step synthesis and near-infrared luminescent properties of Er3+ and Ni2+ doped single-crystalline Al18B4O33 nanorods

Er(3+) and Ni(2+) doped single-crystalline Al(18)B(4)O(33) nanorods were synthesized by a facile one-step toxic-free combustion method. The products were characterized by x-ray diffraction, transmission electron microscopy, selected area electron diffraction, and integrated and time-resolved photoluminescence (PL) measurements. The phase purity, morphology, and PL properties of Er(3+) and Ni(2+) doped Al(18)B(4)O(33) nanorods can be readily controlled by tailoring the annealing temperature. The mechanism for the formation of Al(18)B(4)O(33) nanorods with different aspect ratio is discussed. Er(3+) doped Al(18)B(4)O(33) nanorods show strong PL centered at 1531 nm, while Ni(2+) doped products show superwide PL with a full width at half maximum of up to 250 nm. These aluminum borate nanostructures are promising building blocks for optoelectronics nanodevices.

Nanocell fabrication on GaSb at room temperature and cryogenic temperature

Nanocell fabrication on GaSb (100) is performed at room temperature and 130 K utilizing 30 keV Ga+ in a focused ion beam system. Nanocell lattices with 80 – 300 nm dot intervals were realized at room temperature. It was shown that fabrication at 130 K has some advantages comparing to fabrication at room temperature. At low temperature, nanocell lattices are easily obtained in wider range of dot interval, without secondary void formation.

Characteristics of ZnO Wafers Implanted with 60 keV Sn+ Ions at Room Temperature and at 110 K

ZnO wafers implanted with 60 keV Sn+ ions at room temperature (RT) and at 110 K are investigated by means of X‐ray diffraction (XRD) and photoluminescence (PL) techniques. The effect of implantation temperature is evident in the XRD and PL data. A yellow‐orange (YO) band near 600 nm appears in the PL spectra of the ZnO wafers implanted to the doses of 4×1014 and 8×1014 ions/cm2 at RT. The intensity of this band increases and the peak position blue‐shifts after illumination of the samples with the 325 nm line of a He‐Cd laser. The PL data suggests that the CB (conduction band)→VO+ and Zni+→VZn− transitions contribute to the photoemission of the YO band.

Fabrication of Tetragonal and Close‐Packed Nano‐cell Two‐Dimensional Lattices by Ga+ beam on InSb Surface

In order to develop the novel nano‐fabrication technique utilizing the behavior of the point defects induced by ion implantation, two kinds of nano‐cell two‐dimensional lattices, tetragonal (T) and close‐packed (CP) lattices, are fabricated on InSb surface by focused ion beam (FIB) and the development of the lattices is examined comparing with each other. Lattices consisting of voids were formed by 1.13×105 ions of 50 keV Ga+ per one void in both patterns and developed by ion irradiation using the image scanning mode of FIB. The change of cell in CP pattern with irradiation was similar to that in T pattern; the diameter increased with scan times and was saturated. However the suppression of the secondary void formation was clearly observed in CP pattern. The range of the dot interval and ion dose yielding ordered nano‐cell structures was evaluated.

Nano‐cell Fabrication Using the Behavior of Point Defects Induced by Ion Implantation

The authors’ finding that cellular structure is formed on the GaSb, InSb and Ge surfaces by ion implantation is introduced. A novel nano‐fabrication technique based on the authors’ discovery, which consists of a top‐down process and a bottom‐up process, is performed on a GaSb surface using focused ion beam. In the top‐down procedure, a two‐dimensional lattice of voids (initial structure) is created by irradiation with a focused ion beam. Then, the bottom‐up process for developing the initial structure into nano‐cell structures is performed using the image scanning mode of FIB. The structure is observed by FIB and SEM. The possibilities of the new technique are examined, varying the ion acceleration voltage and the ion dose.