Junyi Chen

Doping and hydrogen passivation of boron in silicon nanowires synthesized by laser ablation

Local vibrational modes of boron (B) in silicon nanowires (SiNWs) synthesized by laser ablation were observed at about 618 and 640cm−1 by Raman scattering measurements. Boron doping was performed during the growth of SiNWs. Fano [Phys. Rev. 124, 1866 (1961)] broadening was also observed in the Si optical phonon peak. These results prove that B atoms were doped in the SiNWs. Hydrogen (H) passivation of B acceptors in the SiNWs was also investigated. A broad peak was observed at around 650–680cm−1 after hydrogenation, demonstrating that B dopants were passivated by the formation of the well-known H–B passivation centers.

Codoping of boron and phosphorus in silicon nanowires synthesized by laser ablation

Codoping of boron (B) and phosphorus (P) atoms was performed during the synthesis of silicon nanowires (SiNWs) by laser ablation. The observation of a local vibrational mode of B clearly showed B doping in codoped SiNWs, while Fano broadening due to heavy B doping disappeared, indicating compensation by P donors. The electrospin resonance signal of conduction electrons also disappeared due to compensation by B acceptors. These results indicate that codoping of B and P atoms was achieved in SiNWs during laser ablation.

Observation of leakage sites in a hafnium silicon oxynitride gate dielectric of a metal-oxide-semiconductor field-effect transistor device by electron-beam-induced current

Leakage sites in hafnium silicon oxynitride gate dielectrics of metal-oxide-semiconductor field-effect transistors were directly identified by means of electron-beam-induced current (EBIC) technique. Leakage sites were observed as bright spots mostly on the periphery of gate. With the gate bias increasing, the EBIC current of bright spots increased exponentially, but the number of bright spots did not increase.

Carrier Recombination Activities and Structural Properties of Small-Angle Boundaries in Multicrystalline Silicon

The carrier recombination activities of small angle (SA) grain boundaries (GBs) in multicrystalline Si (mc-Si) were systematically investigated by electron-beam-induced current (EBIC). At 300 K, general SA-GBs with tilt angle from 0° to 10° showed weak EBIC contrast (0- 10%) with the maximum appeared at 2°. At low temperature (100 K), all the SA-GBs showed strong EBIC contrast despite the tilt angle. Possible explanations for the variation of the EBIC contrast were discussed in terms of boundary dislocations.

Diffused back surface field formation in combination with two-step H2 annealing for improvement of silicon nanowire-based solar cell efficiency

Silicon nanowire (SiNW)-based solar cell fabrication was developed using a combination of diffused back surface field (BSF) formation and two-step H2 annealing for greater efficiency enhancement. Two different n-SiNW structures synthesized by metal-catalyzed electroless etching and nanoimprinting followed by Bosch process were used as substrates to fabricate single-junction solar cells with chemical vapor deposition grown p-Si shell layer. Without BSF formation, shell layer coverage of nanoimprinted SiNW solar cells fabricated using two-step H2 annealing was optimized and the H2 annealing effect on the shell layer crystallinity was investigated using transmission electron microscopy. Then, the effects of combined H2 annealing process for BSF formation together with shell layer treatment were observed under various annealing times. Enhancement of ~1.5% absolute efficiency of both SiNW-based solar cells was achieved. Reduction of carrier recombination by BSF layer accompanied with the reduction of the defect density on n-SiNW surfaces and inside p-Si layer could be accomplished.

Pencil-shaped silicon nanowire synthesis and photovoltaic application

Pencil-shaped silicon nanowires (SiNWs) were synthesized by colloidal lithography and inductively coupled plasma reactive ion etching for photovoltaic application. Light reflectance of below 10% could be obtained by the asymmetric pencil-shaped SiNW array. The pencil-shaped SiNW structure and properties were investigated and compared with metal catalyzed electroless etching (MCEE) and nanoimprinted SiNWs. Single-junction solar cells consisting of pencil-shaped n-SiNW substrates and p-Si shell layer grown by chemical vapor deposition were fabricated. A combination of two-step H2 annealing and back surface field formation was applied to improve the solar cell properties. Good crystal quality and surface of pencil-shaped SiNWs provided an excellent solar cell junction interface. The great light trapping of the pencil-shaped SiNW solar cell could enhance the conversion efficiency by more than 0.6% compared to the solar cells using MCEE and nanoimprinted SiNWs.

Observation of Leakage Sites in High-k Gate Dielectrics in MOSFET Devices by Electron-Beam-Induced Current Technique

We have succeeded in imaging the leakage sites of hafnium silicate gate dielectrics of metal-oxide-semiconductor field-effect transistors (MOSFETs) by using electron-beam-induced current (EBIC) method. Leakage sites of p-channel MOSFETs were identified as bright spots under appropriate reverse bias condition when the electron beam energy is high enough to generate carriers in the silicon substrate. Most of the leakage sites were observed in the peripheries of shallow trench isolation. These results suggest that some process induced defects are the cause of leakage in these MOSFETs. Our observation demonstrates the advantage of EBIC characterization for failure analysis of high-k MOSFETs.

Trap-Related Carrier Transports in p-FET with Poly-Si/HfSiON Gate Stack

1 National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan Phone: +81-29-851-3354 ex 8897 E-mail: CHEN.Jun@nims.go.jp 2 Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan 3 Semiconductor Leading Edge Technology, Inc. (SELETE), 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan 4 Nanotechnology Research Laboratories, Waseda University, 513 Wasedatsurumaki-cho, Shinjuku, Tokyo162-0041, Japan

Phonon Confinement and Impurity Doping in Silicon Nanowires Synthesized by Laser Ablation

The effect of phonon confinement and impurity doping in silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The diameter of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs’ surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement. Boron doping was also performed during the growth of SiNWs. Local vibrational modes of boron (B) in silicon nanowires (SiNWs) synthesized by laser ablation were observed at about 618 and 640 cm–1 by Raman scattering measurements. Fano broadening due to coupling between discrete optical phonons and the continuum of interband hole excitations was also observed in the Si optical phonon peak. These results prove that B atoms were doped in the SiNWs.