Akira Heya

The low-temperature formation of nanocrystalline Si (nc-Si) in SiO_x is one of key technologies for the realization of high-quality solar cells. We proposed a low-temperature crystallization method by soft X-ray at BL07A in the synchrotron radiation facility, NewSUBARU. It is known that the crystallization temperature of amorphous Si (a-Si) film on SiO_2 substrate was reduced by about 100℃. The a-Si in SiO_x film was crystallized by atomic migration via electron excitation by soft X-ray irradiation at the photon energy near the core level of Si2p. The size of nc-Si prepared at 660℃ by soft X-ray irradiation was estimated to 16.8 nm from the peak position of Raman spectra. The nc-Si can be formed by soft X-ray irradiation at low temperature.

The important problem is to control the energy loss by the recombination of the holes and the electrons which are excited by the incident solar beam. We present the micro-wall solar cell that has the metal-insulator-semiconductor (MIS) diode at the side wall of the power generation layer. It was found that the increase ratio of conversion efficiency under the gate voltage application is 2.8 times at the maximum in comparison with non-gate application corresponding to the conventional solar cell.

The carrier behavior in DNA was examined using the DNA channel/SiO_2/Si gate structure, hi this case, electrodes with a gap of 120 nm using a substrate Si was prepared and DNA was fixed between the electrodes. The dI_D/dV_D shows the maximum value at the drain voltage of 0.7 V. This phenomenon relates to the trapped and detrapped electrons in DNA. The electrons were trapped by guanine-base, and they were detrapped by the electric field in the channel. In the case of p^+Si, the holes of majority earners are emitted from the drain electrodes by recombination of electrons and holes in the DNA channel thought the mass action law.

The low-temperature formation of nanocrystalline Si (nc-Si) in SiO_x is one of key technologies for the realization of high-quality solar cells. We proposed a low-temperature crystallization method by soft X-ray at BL07A in the synchrotron radiation facility, NewSUBARU. It is known that the crystallization temperature of amorphous Si (a-Si) film on SiO_2 substrate was reduced by about 100℃. The a-Si in SiO_x film was crystallized by atomic migration via electron excitation by soft X-ray irradiation at the photon energy near the core level of Si2p. The size of nc-Si prepared at 660℃ by soft X-ray irradiation was estimated to 16.8 nm from the peak position of Raman spectra. The nc-Si can be formed by soft X-ray irradiation at low temperature.

The important problem is to control the energy loss by the recombination of the holes and the electrons which are excited by the incident solar beam. We present the micro-wall solar cell that has the metal-insulator-semiconductor (MIS) diode at the side wall of the power generation layer. It was found that the increase ratio of conversion efficiency under the gate voltage application is 2.8 times at the maximum in comparison with non-gate application corresponding to the conventional solar cell.

The carrier behavior in DNA was examined using the DNA channel/SiO_2/Si gate structure, hi this case, electrodes with a gap of 120 nm using a substrate Si was prepared and DNA was fixed between the electrodes. The dI_D/dV_D shows the maximum value at the drain voltage of 0.7 V. This phenomenon relates to the trapped and detrapped electrons in DNA. The electrons were trapped by guanine-base, and they were detrapped by the electric field in the channel. In the case of p^+Si, the holes of majority earners are emitted from the drain electrodes by recombination of electrons and holes in the DNA channel thought the mass action law.

Polycrystalline (poly-) Si film by laser annealing is attractive for thin film transistor on a polymer substrate as well as on a glass substrate. We have proposed a visible-laser-induced lateral crystallization (VILC) for decreasing process temperature. Visible laser is irradiated onto a polycrystalline Si film before or after ultraviolet laser irradiation. Lateral growth is enhanced by visible laser heating at the grain boundary since the absorbance of the grain boundary is larger than that of the in-grain.

Polycrystalline (poly-) Si film by laser annealing is attractive for thin film transistor on a polymer substrate as well as on a glass substrate. We have proposed a visible-laser-induced lateral crystallization (VILC) for decreasing process temperature. Visible laser is irradiated onto a polycrystalline Si film before or after ultraviolet laser irradiation. Lateral growth is enhanced by visible laser heating at the grain boundary since the absorbance of the grain boundary is larger than that of the in-grain.

To realize a ultrathin junction with lOnm depth, a novel activation method of B dopant using soft X-ray undulator was examined. As the photon energy of the irradiated soft X-ray closed to the energy of core level of Si 2p, the activation ratio increased. The effect of soft X-ray irradiation on B activation was remarkable at temperature lower than 400℃. The activation energy of B activation by soft X-ray irradiation (0.06 eV) was lower than that of B activation by thermal annealing (0.18 eV). The activation of B dopant confirmed at low temperature, although the activation ratio shows small values of 6.2x 10^<-3> at 110℃. Furthermore the sheet resistance was slightly reduced by using a cooled holder even at 35℃. At first, the electron at Si2p level was excited by soft X-ray. Next, the Si atoms were ionized and Coulomb repulsion was generated between the ionized Si atoms. The atomic movement of Si atoms was enhanced by ionization and local phonon composition. The crystallinity of Si was recovered. In addition, the substitution of B atom into Si lattice site is occurred via knock-on effect.

We examined dependence of the crystallization for a-Ge and a-SiGe on the photon energy. In the storage-ring current of 75 mA, the a-Ge films were crystallized in the photon energy of 100 eV at the sample temperature of 380℃, while they were not crystallized in the photon energy of 130eV at higher temperature of 410℃. Thus, the crystallization of a-Ge films by soft X-ray irradiation depends on the photon energy in comparison with thermal effect. TEM observation was carried out for the a-SiGe multilayer film with gradual change in composition after soft X-ray irradiation. A crystalline SiGe grain formed in the a-SiGe multilayer film. The interface positions and compositions of each layer in the crystalline grain were similar to those of amorphous matrix. The multi layers in the crystalline grain had crystallographic orientation relationship.

The energy loss of solar cell due to the recombination of holes and electrons which are excited by the incident solar beam is approximately 20% of all the loss-mechanisms. We presented the novel structure of the solar cell that has the metal-oxide-semiconductor (MOS) diode at the side wall of the power generation layer. The purpose of this research is to discuss the optimum structure of solar cell where pn or pin junction is formed parallel to the light receiving surface using the device simulation.

The energy loss of solar cell due to the recombination of holes and electrons which are excited by the incident solar beam is approximately 20% of all the loss-mechanisms. We presented the novel structure of the solar cell that has the metal-oxide-semiconductor (MOS) diode at the side wall of the power generation layer. The purpose of this research is to simulate influence of the field-effect on the recombination of carriers and show the increase of the conversion efficiency of the solar cell.

We produced electrodes with a gap of about 100nm by using the substrate Si, DNA was fixed between the electrodes, and it has reported that there is a charge retention characteristics. The carrier behavior of the DNA was examined using the DNA channel/SiO2/Si gate structure. The followings were clarified. 1) The phenomenon that the dID/dVD characteristics shows the maximum value indicates that the captured electrons in the guanine-base are detrapped by the electric field in the channel. 2) The refresh process of the DNA Memory FET is influenced by both the voltage applied to the gate and the duration for the refresh process. The number of the detrapped electrons increases as the refresh voltage increases. 3) The captured energy level of electron is near the valence band edge in the band gap of guanine-base and its density is large.

We developed a new low-temperature crystallization method, SXC (Soft X-ray Crystallization), of amorphous (a-) Si, Ge and Si_xGe_<1-x> film deposited on a glass substrate by soft x-ray irradiation using short undulator as a light source at NewSUBARU SR facility. Quasi-nucleation followed by grain growth at low temperature proceeds under a solid phase. The fundamental process of the SXC-method is a local excitation of core electrons to vacuum level by photons followed by atom movement due to coulomb repulsion, which results in quasi-nucleation. Therefore, the grain growth occurs lower temperature than the conventional (conv.) thermal crystallization. The SXC-method realizes the threshold temperature of crystallization for a-Si, Ge and Si_xGe_<1-x> film by approximately 100 degree C under the present conditions than conv. Method.

We developed a new low-temperature crystallization method, SXC (Soft X-ray Crystallization), of amorphous (a-) Si, Ge and Si_xGe_<1-x> film deposited on a glass substrate by soft x-ray irradiation using short undulator as a light source at NewSUBARU SR facility. Quasi-nucleation followed by grain growth at low temperature proceeds under a solid phase. The fundamental process of the SXC-method is a local excitation of core electrons to vacuum level by photons followed by atom movement due to coulomb repulsion, which results in quasi-nucleation. Therefore, the grain growth occurs lower temperature than the conventional (conv.) thermal crystallization. The SXC-method realizes the threshold temperature of crystallization for a-Si, Ge and Si_xGe_<1-x> film by approximately 100 degree C under the present conditions than conv. Method.