[en] Direct deposition of Si by a 200 eV Si²⁺ focused ion beam (FIB) on an Au-evaporated substrate was performed in oxygen atmosphere under a pressure of 10^-5 Torr. From Auger electron spectroscopy (AES) measurement, it was found that a large amount of oxygen was incorporated in the deposited material, but clear chemical shift in Si AES signal was not observed. From Raman scattering measurement, two broad signals, as well as large amorphous-Si (a-Si) signals, were observed at about 1000 and 1600 cm^-1. A small and broad signal was also observed at about 1550 cm^-1, which indicates the existence of oxygen molecules inside the deposited material

[en] Effects of low energy ion beam induced damages on transport properties of a two-dimensional electron gas (2DEG) system in GaAs/AlGaAs heterostructures have been investigated. 1 keV Ar ions were irradiated on the sample surface at several ion doses (10¹¹ - 10¹³ cm^-2). Carrier density and electron mobility of the 2DEG formed at about 90 nm below the GaAs/AlGaAs heterostructure surface were estimated at 1.5 K by Hall resistance and longitudinal resistance measurements before and after annealing at 400 C for 10 min in an Ar gas ambient. The temperature dependence of those values was also measured for as-grown and for 10¹³ cm^-2 ion irradiated and subsequently annealed samples. Typical results show that carrier density and mobility are not degraded severely by Ar ion irradiation at doses of 10¹³ cm^-2 and suggest the possibility to fabricate buried structures in GaAs/AlGaAs heterostructures using low energy Si focused ion beam (FIB) irradiation and subsequent in situ overlayer growth by MBE

[en] Fifteen kiloelectronvolts focused Mn ion beam was implanted on molecular beam epitaxy-grown Si-δ-doped GaAs which was mesa-etched to form Hall-bar geometry and annealed at 840 deg. C for 10 s in hydrogen and argon mixed gas ambient. Au-Si-Mn liquid metal alloy ion source was fabricated to perform both Mn and Si ion implantation. From the Hall resistance measurement at 77 K, non-linear behavior and hysteresis were observed in the Hall resistance in the Mn implanted region. The present result indicates that a ferromagnetic layer is formed in GaAs by the Mn ion implantation

[en] We have investigated room-temperature photoreflectance (PR) spectra in Er-doped InP grown by low-pressure organometallic vapor phase epitaxy. A new feature is clearly observed at 1.31 eV, accompanied with a feature due to the bandgap transition at 1.35 eV. The new feature is attributed to a transition involving an Er trap. The transition energy is independent of both doping processing techniques and concentrations of Er in the layers. The PR spectral width of the trap transition energy described by the broadening parameter, increases linearly with the logarithm of Er concentrations. copyright 1997 American Institute of Physics

[en] We have investigated sub-picosecond-range carrier-transport processes in undoped GaAs/n-type GaAs (i-GaAs/n-GaAs) epitaxial layer structures with various i-GaAs-layer thicknesses d ranging from 200 to 2000 nm, focusing on the relation between carrier-transport processes and terahertz electromagnetic wave frequency. Initially, using numerical simulation and photoreflectance measurement, we confirm that a decrease in d enhances the built-in electric field in the i-GaAs layer. In the time-domain terahertz waveform, it is observed that the intense monocycle oscillation induced by the surge current of photogenerated carriers, the so-called first burst, is followed by the oscillation patterns originating from the coherent GaAs longitudinal optical (LO) phonon. From the Fourier power spectra of the terahertz waveforms, it is clarified that the decrease in d causes a high frequency shift of the band of the first burst. Consequently, we conclude that, in the sub-picosecond time range, the photogenerated carriers are monotonously accelerated by the built-in electric field without being affected by intervalley scattering. The present conclusion signifies that the frequency-tunable terahertz emitters are realized by controlling i-GaAs-layer thickness. We also find the intensity of the coherent LO phonon band is enhanced by a decrease in d.

[en] The formation of porous structures of nanometre size (nanoporous structures) on germanium (Ge) surfaces by focused ion beam (FIB) irradiations was investigated using various FIB conditions such as ion species, irradiation energies, total fluences, fluence rates, and incident angles. FIB-irradiated regions were observed using a scanning electron microscope and an atomic force microscope. It is found that, using a focused Ga ion beam (Ga FIB) at an energy of 100 keV, the irradiated Ge surface swelled up to ion fluence of 2 x 10¹⁷ cm^-2 with nanoporous structures and then was etched for larger fluences. The shape of swollen nanoporous structures depended on the fluence rate and the incident angle of the Ga FIB. However, such porous structures were observed neither for low-energy (15-30 keV) FIB irradiations using Si and Au ions nor for high-energy (200 keV), heavy ion (Au) irradiation. These observations might be helpful in discussing the formation mechanisms of the nanoporous structures on Ge surfaces by ion beam irradiations. Fabrication of patterned structures at selected regions on the Ge surface was demonstrated without using any masks

[en] The possibility of forming GaN layers on Ga-implanted SiN surfaces was investigated using electron cyclotron resonance-assisted molecular beam epitaxy (MBE). It is found that the GaN layer initially formed on the SiN surface by Ga implantation at room temperature was amorphous-like, but become to polycrystalline after annealing at 650 deg. C for 3 min in vacuum. After the MBE growth of GaN, a grain structure of h-GaN was observed on the Ga-implanted SiN surface. The crystallinity of the GaN grown was, however, decreased upon increasing the Ga ion fluence on the SiN surface, which might be due, at least partly, to the formation of Ga clusters by the excess Ga implanted. The present results indicate the possibility of forming patterned GaN layers on SiN by selective Ga implantation on the SiN substrate, using a focused ion beam

[en] Magnetic and chemical properties of Mn-implanted surfaces of a GaAs substrate were investigated using a magnetic force microscope (MFM) and X-ray photoemission spectroscopy (XPS). The Mn implanted region was changed to a grain structure after annealing at 840 deg. C for 10 s, and ferromagnetic characteristics were observed in each grain. From the XPS spectra, it was found that implanted Mn was chemically bonded with other elements, indicating the formation of ferromagnetic materials such as GaMn and MnAs