Masafumi Taniwaki

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.

Tip artifact in atomic force microscopy observations of InAs quantum dots grown in Stranski–Krastanow mode

The tip artifact in atomic force microscopy (AFM) observations of InAs islands was evaluated quantitatively. The islands were grown in the Stranski–Krastanow mode of molecular beam epitaxy. The width and height of the islands were determined using transmission electron microscopy (TEM) and AFM. The average [1¯10] in-plane width and height determined using TEM excluding native oxide were 22 and 7nm, respectively; those determined using AFM including the oxide were 35 and 8nm, respectively. The difference in width was due to the oxide and the tip artifact. The sizes including the oxide were deduced from TEM observations to be a width of 27nm and a height of 6nm with correction for the thickness of the oxide. The residual difference of 8nm between the width determined using AFM and that determined using TEM including the oxide was ascribed to the tip artifact. The results enable us to determine the actual size of the islands from their AFM images.

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.

Photoluminescence of an Al0.5Ga0.5As/GaAs multiple quantum well in the temperature range from 5 to 400 K

Photoluminescence (PL) of an unintentionally doped Al0.5Ga0.5As/GaAs multiple quantum well (MQW) has been measured at temperatures from 5 to 400 K. It was found that the ratio of the intensity of the n=1 electron-light hole transition (1e-1lh) to that of the n=1 electron-heavy hole transition (1e-1hh) can be described by an exponential function of reciprocal temperature. The excitation-power dependence of the 1e-1hh transition PL intensity measured at temperatures from 5 to 296 K in steps of 15–20 K showed that the relative contribution of free-carrier recombination gradually increases from 5 to 120 K and then remains constant. This tendency was confirmed by the temperature dependence of the energy difference between the 1e-1hh transition and the bulk GaAs band gap.

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.

Mössbauer Analysis of 57Fe Substituted for Cu in 1212-Phase (Pb,Cu)Sr2(Y,Ca)Cu2Oz Superconductor

57Fe Mossbauer effect in the 1212-phase superconductor is studied by comparison with that in the 123-phase. Spectra at room temperature consist of three doublets (Dl with Δ = 0.56 mm/s, D2 with 1.01 mm/s, D3 with 1.80mm/s), and two antiferromagnetically split sextets (S1 with H i ,= 472 kOe, S2 with 381 kOe) are observed at low temperatures. D3(= S1) attributes to Fe4+ (S = 2) at Cu(1) site and D1(= S2) do to Fe3+ (S=5/2) at Cu(2).