Masafumi Taniwaki

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.

Pulsed laser excitation power dependence of photoluminescence peak energies in bulk ZnO

Photoluminescence (PL) spectra of hydrothermal bulk ZnO were measured in the temperature range from 5 to 298u2009K. The sample was excited by means of the 266-nm line of an Nd3+: YAG Q-switched pulsed laser with numerous average excitation powers in the range from 0.33 to 7.50 mW. At constant temperatures, the most intense PL peak red-shifts with average excitation power, whereas positions of other near-band-edge peaks remain unchanged. It was experimentally proven that the red-shift is not due to local heating at the excited spot. Rather, it is due to relaxation of photoexcited carriers to lower energy transitions as the most intense transition is saturated by high excitation photon density. Furthermore, the temperature dependence of energy of the most intense PL peak was fitted with the Varshni equation. The Varshni coefficients α and β decrease with increasing pulsed laser excitation power.

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 4.1u2009×u20091013 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.

Investigation of Wafer-Bonded InAs/Si Heterojunction by Transmission Electron Microscopy

An InAs/Si heterojunction formed by a wet wafer bonding method with an annealing temperature of 350 °C was investigated by transmission electron microscopy (TEM). InAs and Si were observed to be uniformly bonded without any voids in a 2-µm-long field of view in a bright-field TEM image. A high-resolution TEM image revealed that, between the InAs and Si lattice images, there existed a transition layer having an amorphous-like structure 10–12 nm thick, which had the role of atomically combining the two crystals. The transition layer was separated into two layers of different brightnesses in a high-angle annular dark-field scanning TEM image. The distributions of In, As, Si, and O atoms in the vicinity of the heterointerface were examined by energy dispersive X-ray spectroscopy. The amounts of In, As, and Si atoms gradually changed within a 20-nm-thick intermediate layer including the transition layer. Accumulated O atoms were detected in the transition layer.

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 8×1014u2009ions/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 (conductionu2009band)→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.

Secondary defects induced by ion and electron irradiation of GaSb

Secondary defects induced by ion and electron irradiation up to 6u2009dpa (displacements per atom) at liquid-nitrogen temperature in GaSb thin films are compared. For Sn ion (60u2009keV) irradiation, voids were observed. However, for high-energy electron (2u2009MeV) irradiation, interstitial-type dislocation loops were produced. The densities of voids and interstitial-type dislocation loops were almost equivalent (8u2009×u20091014u2009voids/m2 and 3u2009×u20091014u2009loops/m2) after irradiations at the same damage level of 6u2009dpa. It is concluded that the formation of voids by ion irradiation follows the creation of localised vacancy defects in cascade damage.