Kiyoshi Miyake

Photovoltaic properties of ion-beam synthesized β-FeSi2/n-Si heterojunctions

We present the first evident photovoltaic responses from ion-beam synthesized (IBS) polycrystalline p-type β-FeSi2/n-Si(100) heterojunctions. The triple ion implantation and subsequent annealing at 800°C provided polycrystalline continuous layers ∼60-nm thick with large crystalline grains of ∼10 μm. The high temperature and long annealing time were very effective in amplifying the photovoltaic responses from the heterojunctions. We achieved a maximum open-circuit voltage of 0.34 V by 5 mW/cm2 of white light illumination. Furthermore, we confirmed that the annealing procedure at 500°C induced the precipitation of the psuedomorphic metallic γ phase, which is detrimental to both rectification and the photovoltaic voltage at the p–n heterojunction.

Effect of substrate bias voltage on the thermal stability of Cu/Ta/Si structures deposited by ion beam deposition

The interfacial reactions of the Cu (100 nm)/Ta (50 nm)/Si structures and their relationship with the microstructure of Ta diffusion barrier are investigated. Ta films were deposited on Si (100) substrates using a non-mass separated ion beam deposition system at various bias voltages ranging from 0 to -200 V. An optimum applied substrate bias voltage of -125 V was found to yield a dominant α-Ta film with a noncolumnar structure, low electrical resistivity (about 40 µΩcm) and smooth surface. A Ta diffusion barrier which was deposited at the optimum bias voltage prevented Cu–Si interaction up to 600°C for 60 min in flowing purified H2, whereas a Ta layer with a columnar structure, deposited at zero bias voltage, degraded at 300°C. Two different reactions of the Cu/Ta (0 V)/Si and the Cu/Ta (-125 V)/Si structures concerning the thermal stability were investigated and discussed on the basis of the experimental results.

Raman spectroscopic study of ion-beam synthesized polycrystalline β-FeSi2 on Si(100)

We examined effects of ion implantation doses, annealing temperature and time on ion-beam synthesis (IBS) of polycrystalline β-FeSi2 using Raman spectroscopy. It was confirmed that at very low Fe concentration doses (up to 1×1016 ions/cm2), fine grains of β-FeSi2 and a small amount of fluorite γ-FeSi2 may precipitate after annealing at 800°C. In the case of high dose (>1×1017 ions/cm2), the clear Raman lines showed that β-FeSi2 grows after annealing at 800°C. However, we observed an outstanding Raman line at 324 cm−1 and broad features at 300–450 cm−1 after annealing at 600 and 700°C. These Raman features can be considered to be due to presence of γ-FeSi2 and lattice imperfections in the samples. Furthermore, we evaluated improvement of crystalline quality with increasing the annealing time and temperature using a clear blue shift of the Raman line and increase of the intensity-ratio of two Raman lines at ∼192 and ∼246 cm−1, θ=(I192/I246).

Infrared-Photovoltaic Responses of Ion-Beam Synthesized β-FeSi 2 / n -Si Heterojunctions

Photoresponses of photovoltaic cells using ion-beam synthesized (IBS) polycrystalline p + -β-FeSi 2 /n-Si heterojunctions were examined in an infrared (IR) wavelength region. At room temperature, an evident photoresponse due to an internal photoemission from trap levels in β-FeSi 2 with the threshold energy Φ=0.62 eV was observed at 0.6-0.87 eV. The pronounced increase of a photoresponse corresponding mostly to an interband transition in β-FeSi 2 was observed at 0.87-1.1 eV. The maximum dominated by a surface recombination process appeared around ∼1.2 eV. The surface recombination rate of ∼10 4 cm/s was estimated. The quantum efficiency was ∼60 % in the 0.8-1.0 µm wavelength region and ∼14 % around the band-gap of βFeSi 2 .

Magnetic Properties of β-FeSi2 Semiconductor

High-quality crystals of β-FeSi2 are ion-beam synthesized on the surface of a floating-zone(FZ)-grown Si wafer, and superconducting quantum interference device (SQUID) and ESR measurements are performed. β-FeSi2 semiconductors exhibit paramagnetic properties, and the Weiss temperature is positive near room temperature. The magnetic susceptibility changes anomalously with temperature.

Preparation of high-purity Cu films by non-mass separated ion beam deposition

Cu films were deposited on Si(1 0 0) substrates by applying a negative substrate bias voltage using non-mass separated ion beam deposition (IBD) method. By the SIMS results with Cs þ ion beam, the Cu film deposited at VS ¼ 0 V was found to contain more impurities than the Cu film deposited at VS ¼� 50 V. On the other hand, from the SIMS results with O þ ion beam, it was found that elements which are easy to be positive ions such as B, Mg, Na, Al, K, Ca and Fe seem to be increased slightly as compared to the those of the Cu film deposited at VS ¼ 0 V. As a result, higher-purity Cu film deposited at VS ¼� 50 V could be obtained in comparison with the film deposited at VS ¼ 0 V. The purification effect of the Cu film deposited at VS ¼� 50 V was described in details. � 2003 Elsevier Science B.V. All rights reserved.

High purity RF-sputter type metal ion source for non-mass-separated ion beam deposition

High purity RF-sputter type metal ion source has been developed for non-mass separated ion beam deposition. An Fe or Cu rod target of purity 99.999% or 99.9999%, respectively, was DC-sputtered inside an RF inductively generated Ar plasma. Optical emission spectroscopy from the plasma region (Fe case) indicated that emission from Fe* becomes larger than that of Ar* when DC bias voltage of -1 kV was applied. This result agreed with our previous mass spectroscopic results that Fe/sup +/ ion intensity overcomes that of Ar/sup +/ because of an efficient Penning ionization of sputtered and evaporated Fe particles. Cu films deposited on Si substrate at RT with the ion source showed non-columnar structure at a substrate bias voltage of -150 V, whereas only columnar structure was obtained with no bias voltage. This tendency qualitatively agreed with the case of Fe film formation obtained in our mass separated IBD.