Showing papers by "Masashi Kurosawa published in 2015"

High hole mobility tin-doped polycrystalline germanium layers formed on insulating substrates by low-temperature solid-phase crystallization

Abstract: We investigated the effects of incorporation of 0%–2% tin (Sn) into amorphous germanium (Ge) on its crystallization behavior and electrical properties. Incorporation of only 0.2% Sn caused the polycrystallization temperature of Ge to lower from 450 to 430 °C, while a polycrystalline Ge1−xSnx layer with high crystallinity compared to that of polycrystalline Ge was formed by incorporation of 2% Sn. A polycrystalline Ge1−xSnx layer with a low Sn content of 2% annealed at 450 °C exhibited a Hall hole mobility as high as 130 cm2/V s at room temperature even though it possessed a small grain size of 20–30 nm. The Hall hole mobility of a poly-Ge1−xSnx layer with an Sn content of 2% was four times higher than that of a polycrystalline Ge layer and comparable to that of single-crystalline silicon.

Near-infrared light absorption by polycrystalline SiSn alloys grown on insulating layers

Abstract: High-Sn-content SiSn alloys are strongly desired for the next-generation near-infrared optoelectronics. A polycrystalline growth study has been conducted on amorphous SiSn layers with a Sn-content of 2%–30% deposited on either a substrate of SiO2 or SiN. Incorporating 30% Sn into Si permits the crystallization of the amorphous layers at annealing temperatures below the melting point of Sn (231.9 °C). Composition analyses indicate that approximately 20% of the Sn atoms are substituted into the Si lattice after solid-phase crystallization at 150–220 °C for 5 h. Correspondingly, the optical absorption edge is red-shifted from 1.12 eV (Si) to 0.83 eV (Si1−xSnx (x ≈ 0.18 ± 0.04)), and the difference between the indirect and direct band gap is significantly reduced from 3.1 eV (Si) to 0.22 eV (Si1−xSnx (x ≈ 0.18 ± 0.04)). These results suggest that with higher substitutional Sn content the SiSn alloys could become a direct band-gap material, which would provide benefits for Si photonics.

Epitaxial growth and crystalline properties of Ge1−x−ySixSny on Ge(0 0 1) substrates

Abstract: We have investigated the influence of tensile and compressive strain on the crystalline structures of Ge 1− x − y Si x Sn y epitaxial layers. The tensile strain in Ge 1− x − y Si x Sn y induces a non-uniform crystallinity of (2 2 0) lattice planes and surface roughening despite the strain magnitude is as small as 0.20%. In contrast, the unstrained or compressive strained Ge 1− x − y Si x Sn y layer exhibits a flat and uniform surface and high crystallinity. We found that the control of the sign of the strain is an important factor to obtain a high quality Ge 1− x − y Si x Sn y layer. Furthermore, substitutional Sn atoms in Ge 1− x − y Si x Sn y epitaxial layer with an Sn content of 10% are thermally stable for annealing at 500 °C.

Reduction of Schottky barrier height at metal/n-Ge interface by introducing an ultra-high Sn content Ge1−xSnx interlayer

Abstract: We investigated the impact of introducing an ultra-high Sn content Ge1−xSnx interlayer on the electrical properties at the metal/Ge interface. We achieved epitaxial growth of a Ge1−xSnx thin layer with an ultra-high substitutional Sn content of up to 46% on a Ge(001) substrate by considering the misfit strain between Ge1−xSnx and Ge. From the current-voltage characteristics of Al/Ge1−xSnx/n-Ge Schottky diodes, we found an increase in the forward current density of the thermionic emission current with increasing Sn content in the Ge1−xSnx interlayer. The Schottky barrier height estimated in Al/Ge1−xSnx/n-Ge diodes decreases to 0.49 eV with an increase in the Sn content up to 46% of the Ge1−xSnx interlayer. The reduction of the barrier height may be due to the shift of the Fermi level pinning position at the metal/Ge interface with a Ge1−xSnx interlayer whose valence band edge is higher than that of Ge. This result enables the effective reduction of the contact resistivity by introducing a group-IV semicond...

Characterization of locally strained Ge1−xSnx/Ge fine structures by synchrotron X-ray microdiffraction

Abstract: We have investigated the formation of the locally strained Ge nanostructure with epitaxial Ge1−xSnx stressors and characterized the microscopic strain field in the Ge1−xSnx/Ge fine-heterostructures by synchrotron X-ray microdiffraction and finite element method (FEM) calculations. We achieved local epitaxial growth of Ge1−xSnx with Sn contents of 2.9% and 6.5%, sandwiching the 25 nm-wide Ge fine line structure. Microdiffraction measurements revealed that out-of-plane tensile strain induced in the Ge line effectively increased with decreasing Ge width and increasing Sn content of Ge1−xSnx stressors, which is in good agreement with FEM calculations. An out-of-plane tensile strain of 0.8% along the Ge[001] direction is induced in a 25 nm-wide Ge line, which corresponds to an in-plane uniaxial compressive strain of 1.4% in the Ge line sandwiched between Ge0.935Sn0.065 stressors.

Effect of Sn on crystallinity and electronic property of low temperature grown polycrystalline-Si1−x−yGexSny layers on SiO2

Abstract: We examined the formation of polycrystalline-Si1−x−yGexSny layers on SiO2 by the solid phase crystallization method. We investigated the impact of Sn incorporation on the polycrystallization, crystallinity, and electrical property of Si1−xGex layers. We found that the polycrystallization time of Si1−x−yGexSny decreases with increasing in the Sn content in the annealing at 500 °C. No Sn precipitation is observed after the crystallization of Si1−x−yGexSny layer with an Sn content of 2%, while severe Sn precipitation is found in the sample with an Sn content of 10%. Moreover, larger grains of polycrystal can be obtained by the incorporation of 2%-Sn with comparison to that without Sn. The enlargement of polycrystalline grain of Si1−x−yGexSny improves in the hole mobility to 74 cm2/V s.

Formation, crystalline structure, and optical properties of Ge1−x−ySnxCy ternary alloy layers

Abstract: We have investigated the crystalline and optical properties of epitaxial layers of the ternary alloy Ge1−x−ySnxCy grown on a Si substrate. We achieved the formation of epitaxial Ge1−x−ySnxCy layers with a C content as high as 2% even with a high C incorporation efficiency. X-ray photoemission spectra and Raman scattering spectroscopy measurements revealed that C atoms preferentially bond with Sn atoms in the Ge matrix, which is considered to enhance C introduction into substitutional sites in Ge with local strain compensation. We also demonstrated the control of the energy bandgaps of epitaxial Ge1−x−ySnxCy layers by controlling Sn and C contents.

Mobility Behavior of Polycrystalline Si1-x-yGexSny Grown on Insulators

Abstract: Takuma Ohmura1, Takashi Yamaha1,2, Masashi Kurosawa1,3, Wakana Takeuchi1*, Mitsuo Sakashita1, Noriyuki Taoka1,, Osamu Nakatsuka1, and Shigeaki Zaima1,3 1 Graduate School of Engineering, Nagoya University, Furo-cho, Nagoya 464-8603, Japan 2 Research Fellow of the Japan Society for the Promotion of Science, Japan 3 EcoTopia Science Institute, Nagoya University, Furo-cho, Nagoya 464-8603, Japan * Wakana Takeuchi: Fax: +81-052-789-2760, and/or e-mail: wtakeuti@alice.xtal.nagoya-u.ac.jp

(Invited) Challenges of Energy Band Engineering with New Sn-Related Group IV Semiconductor Materials for Future Integrated Circuits

Abstract: We report our recent researches and developments of Ge1−xSnx and related group-IV semiconductor materials for the device integration on an Si nanoelectronics platform We investigated the energy band engineering and crystal growth technology for thin films of Ge1−xSnx, Si1−xSnx, and related ternary alloys The energy band structure and band alignment of these semiconductor materials have been experimentally evaluated and discussed Also, the effect of a Ge1−xSnx interlayer on the electronic property at the metal/Ge interface has been investigated

Formation of Ge pn-junction diode by phosphorus doping with liquid immersion laser irradiation

Abstract: We examined the formation of pn-junction didoes on Ge(100), Ge(110), and Ge(111) substrates by P-doping with immersion laser irradiation in phosphoric acid solution at RT We achieved high-concentration phosphorus doping in all orientation, and the maximum concentrations of electrically activated P of 24×1019, 51×1019, and 98×1019 cm−3 for the Ge(100), Ge(110), and Ge(111) substrates, respectively, are obtained with 1000-times laser shots On the other hand, the diffusion depth is significantly different with the orientation, which concerned with the melt depth

Growth of Si1−x−ySnxCy ternary alloy layer on Si(001) substrate and characterization of its crystalline properties

Abstract: We have demonstrated the crystal growth of Si1−x−ySnxCy ternary alloy layers on Si(001) substrates by radio-frequency magnetron sputtering. We have investigated the crystalline properties of the ternary alloy layers and clarified the influence of Sn and C on the crystalline structure of Si1−x−ySnxCy layers. We found that the epitaxial growth temperature of Si1−x−ySnxCy decreased and the island growth was suppressed by the introduction of Sn. The Sn precipitation was also effectively suppressed by C introduction. The substitutional C content of Si1−x−ySnxCy was estimated to be 2.7% and exceeded the thermal equilibrium solid solubility of C into the Si matrix.

Method of forming semiconductor thin film

Abstract: Provided is a method of forming a semiconductor thin film. The method may include forming, on a substrate, a thin film that contains one of Ge, Si, and a SiGe mixture, and Sn in a content of 0.1 atomic % or more to 20 atomic % or less, and applying pulsed laser light to the thin film.

Formation, crystalline structure, and optical properties of Ge

Abstract: We have investigated the crystalline and optical properties of epitaxial layers of the ternary alloy Ge1−x−ySnxCy grown on a Si substrate. We achieved the formation of epitaxial Ge1−x−ySnxCy layers with a C content as high as 2% even with a high C incorporation efficiency. X-ray photoemission spectra and Raman scattering spectroscopy measurements revealed that C atoms preferentially bond with Sn atoms in the Ge matrix, which is considered to enhance C introduction into substitutional sites in Ge with local strain compensation. We also demonstrated the control of the energy bandgaps of epitaxial Ge1−x−ySnxCy layers by controlling Sn and C contents.