Toshiaki Asahi - Profile on Academia.edu (original) (raw)
Papers by Toshiaki Asahi
To Realize the Perfect Crystallization. Recent Developments in InP Crystal Growth
日本結晶成長学会誌, 1998
Low-Frequency Analysis of Shielding Effectiveness Using Pulse Waveform
This paper describes the low-frequency analysis of shielding effectiveness (SE) using a pulse wav... more This paper describes the low-frequency analysis of shielding effectiveness (SE) using a pulse waveform. TheSE of a copper film is estimated using an electromagnetic field simulator. The estimation uses a zero-padding process and a discrete Fourier transform for the analysis frequency range from 10 kHz to 1 GHz. TheSE characteristics using the pulse waveform method are close to those using the sinusoidal waveform method. We found that the pulse waveform method enablesSE analysis in the low-frequency region.
The Japan Society of Applied Physics, Feb 8, 2016
The growth process analysis of the ZnTe layer on the m-plane sapphire substrate with nano-facet structures
ZnTe thin films were grown on m-plane sapphire substrates with nano-faceted structure by MBE. The... more ZnTe thin films were grown on m-plane sapphire substrates with nano-faceted structure by MBE. The growth process of the ZnTe thin film was analyzed by AFM. The influence of the nano-facet on the crystal quality of the epilayer was studied by means of XRD pole figure and PL measurements. It was confirmed that (331)-plane ZnTe layer was formed on the m-plane sapphire substrate with nano-faceted structure and the ZnTe epilayer grown of the nano-facet structure exhibited the single domain structure with high optical properties.
VGF crystal growth and vapor-phase Fe doping technologies for semi-insulating 100 mm diameter InP substrates
100 mm diameter 〈100〉 semi-insulating InP substrates were obtained after conductive undoped wafer... more 100 mm diameter 〈100〉 semi-insulating InP substrates were obtained after conductive undoped wafers were annealed under volatile FeP2 atmosphere. Undoped crystals were grown by the VGF method using a high pressure furnace. In this growth method, we investigated the reduction of the temperature fluctuation by computer simulation for preventing twinning. The temperature fluctuation near the seed crystal could be reduced from ±0.3°C to ±0.03°C after improvement of the hot-zone, based on the simulation results. Semi-insulating InP is conventionally produced by Fe doping during crystal growth. In the conventional doping method, the Fe concentration is varied along the growth axis due to Fe segregation in InP. In order to obtain good homogeneity of Fe concentrations from wafer to wafer, we have developed a new Fe doping technology in which wafers are annealed under volatile FeP2 atmosphere. In this work, we applied this Fe doping technology to 100 mm diameter 〈100〉 InP substrates and could obtain large diameter semi-insulating substrates
Physica status solidi, Mar 24, 2014
ZnTe epilayers were grown on transparent (10-10) oriented (m-plane) sapphire substrates by molecu... more ZnTe epilayers were grown on transparent (10-10) oriented (m-plane) sapphire substrates by molecular beam epitaxy (MBE). Pole figure imaging was used to study the domain distribution within the layer. (211)-oriented ZnTe domains were formed on m-plane sapphire. The presence of only one kind of (211) ZnTe domain formed on the 2º-tilted m-plane sapphire substrates was confirmed. Thus, single domain (211) ZnTe epilayers can be grown on the m-plane sapphire using MBE. Although differences in the crystal structure and lattice mismatch are large, precise control of the substrate surface lattice arrangement result in the formation of high-quality epitaxial layers.
Growth and electro‐optical characterization of ZnMgTe/ZnTe waveguide by molecular beam epitaxy
Physica status solidi, Mar 25, 2014
ZnMgTe/ZnTe/ZnMgTe thin film waveguide with high crystal quality were grown by molecular beam epi... more ZnMgTe/ZnTe/ZnMgTe thin film waveguide with high crystal quality were grown by molecular beam epitaxy (MBE). The in‐plane mismatch between the ZnMgTe cladding layers and ZnTe core layer was about 0.02% which was measured by X‐ray reciprocal space mapping (RSM). It indicated that films were grown coherently with high crystal quality. The Electro‐Optical characterization of waveguide was evaluated using 1.55µm polarized lights and bias applied on the waveguide device from –15 V to +15 V. The de‐pendence of light phase shift passed though the waveguide on the applied voltage bias was studied. The electro‐optical characterization of the waveguide device was about 7% of the theoretical calculation. It could be improved by increasing the resistance ratio between the ZnMgTe/ZnTe/ZnMgTe waveguide structure and substrate so that the electric field applied on the waveguide structure could be improved. It was indicated that the ZnMgTe/ZnTe/ZnMgTe thin film waveguide has the potential to become a high efficiency electro‐optical device. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of the substrate orientation on the ZnTe growth on the sapphire
The Japan Society of Applied Physics, Feb 3, 2017
The Japan Society of Applied Physics, Feb 8, 2016
Ubiquitous services that are genuinely user-friendly to everyone will require technologies that e... more Ubiquitous services that are genuinely user-friendly to everyone will require technologies that enable communication between people and objects in close proximity. Focusing on the naturalness, inevitability, and sense of security conveyed by touching in everyday life, this article describes human area networking technology that enables communication by touching, which we call RedTacton. Here, the human body acts as a transmission medium supporting IEEE 802.3 half-duplex communication at 10 Mbit/s. The key component of the transceiver is an electric-field sensor implemented with an electrooptic crystal and laser light.
Surface Texture and Crystallinity Variation of ZnTe Epilayers Grown on the Step-Terrace Structure of the Sapphire Substrate
Journal of Electronic Materials, Feb 17, 2016
ZnTe/sapphire heterostructures were focused, and ZnTe thin films were prepared on highly mismatch... more ZnTe/sapphire heterostructures were focused, and ZnTe thin films were prepared on highly mismatched sapphire substrates by molecular beam epitaxy. A sapphire substrate possessing an atomically-smooth step-terrace structure was used to improve the crystallinity and morphology of the produced ZnTe film. The growth mode of the ZnTe thin film on a sapphire substrate with an atomically-smooth step-terrace structure was found to shift to a two-dimensional growth mode, and a ZnTe thin film possessing a flat surface was obtained. The crystallographic properties of the ZnTe film suggested that the resulting layer consisted of a single (111)-oriented domain. The photoluminescence property was also improved, and the interface lattice alignment between the ZnTe and sapphire was also affected by the atomically-smooth step-terrace structure.
Characterization of 100 mm diameter CdZnTe single crystals grown by the vertical gradient freezing method
Journal of Crystal Growth, Apr 1, 1995
... [7] LG. Casagrande, DD Marzio, MB Lee, DJ Larson, Jr, M. Dudley and T. Fanning, J. Crystal Gr... more ... [7] LG. Casagrande, DD Marzio, MB Lee, DJ Larson, Jr, M. Dudley and T. Fanning, J. Crystal Growth 128 (1993) 576. ... [14] WP Allred, AA Khan, CJ Johnson, NC Giles and JF Schetzina, Mater. Res. Soc. Symp. Proc. 90 (1987) 103. ...
Journal of Crystal Growth, Jun 1, 2017
Zinc telluride layers were grown on highly-lattice-mismatched sapphire substrates by molecular be... more Zinc telluride layers were grown on highly-lattice-mismatched sapphire substrates by molecular beam epitaxy, and their crystallographic properties were studied by means of X-ray diffraction pole figures. The crystal quality of the ZnTe thin film was further studied by scanning electron microscopy, X-ray rocking curves and lowtemperature photoluminescence measurements. These methods show that high-crystallinity (111)-oriented single domain ZnTe layers with the flat surface and good optical properties are realized when the beam intensity ratio of Zn and Te beams is adjusted. The migration of Zn and Te was inhibited by excess surface material and cracks were appeared. In particular, excess Te inhibited the formation of a high-crystallinity ZnTe film. The optical properties of the ZnTe layer revealed that the exciton-related features were dominant, and therefore the film quality was reasonably high even though the lattice constants and the crystal structures were severely mismatched.
Growth of large-diameter ZnTe single crystals by the vertical gradient freezing method
Journal of Crystal Growth, Jul 1, 2001
ZnTe singles crystals (80mm diameter) were grown by the VGF method without seed crystals. In this... more ZnTe singles crystals (80mm diameter) were grown by the VGF method without seed crystals. In this method, the high-pressure furnace was used and the melt was encapsulated by B2O3 during crystal growth. EPDs of the grown crystals were 5000–10000cm−2. The FWHMs of the rocking curve measured by 4-crystal X-ray diffractometry were around 20arcsec. The crystals grown by the VGF method
Physica status solidi, Mar 1, 2004
ZnTe crystals grown from the melt have Te inclusions. The wafer annealing under Zn pressure was c... more ZnTe crystals grown from the melt have Te inclusions. The wafer annealing under Zn pressure was carried out to reduce Te inclusions in ZnTe wafers. It was found that the cyclic annealing process, where heating and cooling was done cyclically over a temperature range of several tens of degrees, was effective to annihilate the Te inclusions. We obtained the inclusion-free ZnTe crystals by optimising the temperature cycling condition.
Journal of Electronic Materials, Jun 1, 2004
The 80-mm-diameter ZnTe single crystals were successfully obtained by the liquid-encapsulated Kyr... more The 80-mm-diameter ZnTe single crystals were successfully obtained by the liquid-encapsulated Kyropoulos (LEK) method. Both Ͻ100Ͼand Ͻ110Ͼoriented single crystals were reproducibly grown by using ZnTe seed crystals. Furthermore, 80-mm-diameter, Ͻ100Ͼ and Ͻ110Ͼ ZnTe single crystals were obtained by the pulling method. The etch pit densities (EPDs) of the grown crystals by the LEK and pulling methods were lower than 10,000 cm Ϫ2. The strain in the grown crystals by the pulling method was lower than that of LEK crystals.
Growth and characterization of 100 mm diameter CdZnTe single crystals by the vertical gradient freezing method
Journal of Crystal Growth, Apr 1, 1996
Recent bulk crystal growth of CdTe and Cd1 − xZnxTe is reviewed from the viewpoint of large diame... more Recent bulk crystal growth of CdTe and Cd1 − xZnxTe is reviewed from the viewpoint of large diameter single crystal growth. A VGF method based on a multiple-zone furnace has been developed to grow 〈111〉-oriented 100 mm diameter single crystals. By this method, 〈111〉-oriented Cd1 − xZnxTe single crystals can be reproducibly grown. The grown crystals were characterized by the etch pit density measurement, X-ray diffractometry, GD-MS, photoluminescence, Hall measurement and precipitate observation. The growth mechanism is discussed on the basis of the transient solidification.
Physica status solidi, Jul 1, 2000
(a), T. Asahi (a), M. Hanafusa (a), A. Noda (a), A. Arakawa (a), M. Uchida (a), O. Oda (a), Y. Ya... more (a), T. Asahi (a), M. Hanafusa (a), A. Noda (a), A. Arakawa (a), M. Uchida (a), O. Oda (a), Y. Yamada (b), and T. Taguchi (b)
Fe doping and preparation of semi insulating InP by wafer annealing under Fe phosphide vapor pressure
Semi-insulating (SI) InP has been industrially produced by doping Fe atoms as deep acceptors. Fe ... more Semi-insulating (SI) InP has been industrially produced by doping Fe atoms as deep acceptors. Fe concentrations in InP are, however, largely varied from top to tail along the crystal growth axis because of impurity segregation. In the present work, we have examined the possibility of vapor phase doping for producing 50 mm diameter SI InP wafers with constant Fe concentrations by using a wafer annealing procedure. Small amount of Fe was charged with red phosphorus in ampoules in which InP wafers were annealed. It was found that the vapor phase doping is effective for Fe doping in InP. The present technology can be applied for the production of low Fe doped SI InP wafers with the same Fe concentration for all wafers from one InP ingot.
Efficient Method for Estimating Random Errors in Optical Constants Measured with THz-TDS
Conference on Lasers and Electro-Optics 2010, 2010
ABSTRACT
To Realize the Perfect Crystallization. Recent Developments in InP Crystal Growth
日本結晶成長学会誌, 1998
Low-Frequency Analysis of Shielding Effectiveness Using Pulse Waveform
This paper describes the low-frequency analysis of shielding effectiveness (SE) using a pulse wav... more This paper describes the low-frequency analysis of shielding effectiveness (SE) using a pulse waveform. TheSE of a copper film is estimated using an electromagnetic field simulator. The estimation uses a zero-padding process and a discrete Fourier transform for the analysis frequency range from 10 kHz to 1 GHz. TheSE characteristics using the pulse waveform method are close to those using the sinusoidal waveform method. We found that the pulse waveform method enablesSE analysis in the low-frequency region.
The Japan Society of Applied Physics, Feb 8, 2016
The growth process analysis of the ZnTe layer on the m-plane sapphire substrate with nano-facet structures
ZnTe thin films were grown on m-plane sapphire substrates with nano-faceted structure by MBE. The... more ZnTe thin films were grown on m-plane sapphire substrates with nano-faceted structure by MBE. The growth process of the ZnTe thin film was analyzed by AFM. The influence of the nano-facet on the crystal quality of the epilayer was studied by means of XRD pole figure and PL measurements. It was confirmed that (331)-plane ZnTe layer was formed on the m-plane sapphire substrate with nano-faceted structure and the ZnTe epilayer grown of the nano-facet structure exhibited the single domain structure with high optical properties.
VGF crystal growth and vapor-phase Fe doping technologies for semi-insulating 100 mm diameter InP substrates
100 mm diameter 〈100〉 semi-insulating InP substrates were obtained after conductive undoped wafer... more 100 mm diameter 〈100〉 semi-insulating InP substrates were obtained after conductive undoped wafers were annealed under volatile FeP2 atmosphere. Undoped crystals were grown by the VGF method using a high pressure furnace. In this growth method, we investigated the reduction of the temperature fluctuation by computer simulation for preventing twinning. The temperature fluctuation near the seed crystal could be reduced from ±0.3°C to ±0.03°C after improvement of the hot-zone, based on the simulation results. Semi-insulating InP is conventionally produced by Fe doping during crystal growth. In the conventional doping method, the Fe concentration is varied along the growth axis due to Fe segregation in InP. In order to obtain good homogeneity of Fe concentrations from wafer to wafer, we have developed a new Fe doping technology in which wafers are annealed under volatile FeP2 atmosphere. In this work, we applied this Fe doping technology to 100 mm diameter 〈100〉 InP substrates and could obtain large diameter semi-insulating substrates
Physica status solidi, Mar 24, 2014
ZnTe epilayers were grown on transparent (10-10) oriented (m-plane) sapphire substrates by molecu... more ZnTe epilayers were grown on transparent (10-10) oriented (m-plane) sapphire substrates by molecular beam epitaxy (MBE). Pole figure imaging was used to study the domain distribution within the layer. (211)-oriented ZnTe domains were formed on m-plane sapphire. The presence of only one kind of (211) ZnTe domain formed on the 2º-tilted m-plane sapphire substrates was confirmed. Thus, single domain (211) ZnTe epilayers can be grown on the m-plane sapphire using MBE. Although differences in the crystal structure and lattice mismatch are large, precise control of the substrate surface lattice arrangement result in the formation of high-quality epitaxial layers.
Growth and electro‐optical characterization of ZnMgTe/ZnTe waveguide by molecular beam epitaxy
Physica status solidi, Mar 25, 2014
ZnMgTe/ZnTe/ZnMgTe thin film waveguide with high crystal quality were grown by molecular beam epi... more ZnMgTe/ZnTe/ZnMgTe thin film waveguide with high crystal quality were grown by molecular beam epitaxy (MBE). The in‐plane mismatch between the ZnMgTe cladding layers and ZnTe core layer was about 0.02% which was measured by X‐ray reciprocal space mapping (RSM). It indicated that films were grown coherently with high crystal quality. The Electro‐Optical characterization of waveguide was evaluated using 1.55µm polarized lights and bias applied on the waveguide device from –15 V to +15 V. The de‐pendence of light phase shift passed though the waveguide on the applied voltage bias was studied. The electro‐optical characterization of the waveguide device was about 7% of the theoretical calculation. It could be improved by increasing the resistance ratio between the ZnMgTe/ZnTe/ZnMgTe waveguide structure and substrate so that the electric field applied on the waveguide structure could be improved. It was indicated that the ZnMgTe/ZnTe/ZnMgTe thin film waveguide has the potential to become a high efficiency electro‐optical device. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of the substrate orientation on the ZnTe growth on the sapphire
The Japan Society of Applied Physics, Feb 3, 2017
The Japan Society of Applied Physics, Feb 8, 2016
Ubiquitous services that are genuinely user-friendly to everyone will require technologies that e... more Ubiquitous services that are genuinely user-friendly to everyone will require technologies that enable communication between people and objects in close proximity. Focusing on the naturalness, inevitability, and sense of security conveyed by touching in everyday life, this article describes human area networking technology that enables communication by touching, which we call RedTacton. Here, the human body acts as a transmission medium supporting IEEE 802.3 half-duplex communication at 10 Mbit/s. The key component of the transceiver is an electric-field sensor implemented with an electrooptic crystal and laser light.
Surface Texture and Crystallinity Variation of ZnTe Epilayers Grown on the Step-Terrace Structure of the Sapphire Substrate
Journal of Electronic Materials, Feb 17, 2016
ZnTe/sapphire heterostructures were focused, and ZnTe thin films were prepared on highly mismatch... more ZnTe/sapphire heterostructures were focused, and ZnTe thin films were prepared on highly mismatched sapphire substrates by molecular beam epitaxy. A sapphire substrate possessing an atomically-smooth step-terrace structure was used to improve the crystallinity and morphology of the produced ZnTe film. The growth mode of the ZnTe thin film on a sapphire substrate with an atomically-smooth step-terrace structure was found to shift to a two-dimensional growth mode, and a ZnTe thin film possessing a flat surface was obtained. The crystallographic properties of the ZnTe film suggested that the resulting layer consisted of a single (111)-oriented domain. The photoluminescence property was also improved, and the interface lattice alignment between the ZnTe and sapphire was also affected by the atomically-smooth step-terrace structure.
Characterization of 100 mm diameter CdZnTe single crystals grown by the vertical gradient freezing method
Journal of Crystal Growth, Apr 1, 1995
... [7] LG. Casagrande, DD Marzio, MB Lee, DJ Larson, Jr, M. Dudley and T. Fanning, J. Crystal Gr... more ... [7] LG. Casagrande, DD Marzio, MB Lee, DJ Larson, Jr, M. Dudley and T. Fanning, J. Crystal Growth 128 (1993) 576. ... [14] WP Allred, AA Khan, CJ Johnson, NC Giles and JF Schetzina, Mater. Res. Soc. Symp. Proc. 90 (1987) 103. ...
Journal of Crystal Growth, Jun 1, 2017
Zinc telluride layers were grown on highly-lattice-mismatched sapphire substrates by molecular be... more Zinc telluride layers were grown on highly-lattice-mismatched sapphire substrates by molecular beam epitaxy, and their crystallographic properties were studied by means of X-ray diffraction pole figures. The crystal quality of the ZnTe thin film was further studied by scanning electron microscopy, X-ray rocking curves and lowtemperature photoluminescence measurements. These methods show that high-crystallinity (111)-oriented single domain ZnTe layers with the flat surface and good optical properties are realized when the beam intensity ratio of Zn and Te beams is adjusted. The migration of Zn and Te was inhibited by excess surface material and cracks were appeared. In particular, excess Te inhibited the formation of a high-crystallinity ZnTe film. The optical properties of the ZnTe layer revealed that the exciton-related features were dominant, and therefore the film quality was reasonably high even though the lattice constants and the crystal structures were severely mismatched.
Growth of large-diameter ZnTe single crystals by the vertical gradient freezing method
Journal of Crystal Growth, Jul 1, 2001
ZnTe singles crystals (80mm diameter) were grown by the VGF method without seed crystals. In this... more ZnTe singles crystals (80mm diameter) were grown by the VGF method without seed crystals. In this method, the high-pressure furnace was used and the melt was encapsulated by B2O3 during crystal growth. EPDs of the grown crystals were 5000–10000cm−2. The FWHMs of the rocking curve measured by 4-crystal X-ray diffractometry were around 20arcsec. The crystals grown by the VGF method
Physica status solidi, Mar 1, 2004
ZnTe crystals grown from the melt have Te inclusions. The wafer annealing under Zn pressure was c... more ZnTe crystals grown from the melt have Te inclusions. The wafer annealing under Zn pressure was carried out to reduce Te inclusions in ZnTe wafers. It was found that the cyclic annealing process, where heating and cooling was done cyclically over a temperature range of several tens of degrees, was effective to annihilate the Te inclusions. We obtained the inclusion-free ZnTe crystals by optimising the temperature cycling condition.
Journal of Electronic Materials, Jun 1, 2004
The 80-mm-diameter ZnTe single crystals were successfully obtained by the liquid-encapsulated Kyr... more The 80-mm-diameter ZnTe single crystals were successfully obtained by the liquid-encapsulated Kyropoulos (LEK) method. Both Ͻ100Ͼand Ͻ110Ͼoriented single crystals were reproducibly grown by using ZnTe seed crystals. Furthermore, 80-mm-diameter, Ͻ100Ͼ and Ͻ110Ͼ ZnTe single crystals were obtained by the pulling method. The etch pit densities (EPDs) of the grown crystals by the LEK and pulling methods were lower than 10,000 cm Ϫ2. The strain in the grown crystals by the pulling method was lower than that of LEK crystals.
Growth and characterization of 100 mm diameter CdZnTe single crystals by the vertical gradient freezing method
Journal of Crystal Growth, Apr 1, 1996
Recent bulk crystal growth of CdTe and Cd1 − xZnxTe is reviewed from the viewpoint of large diame... more Recent bulk crystal growth of CdTe and Cd1 − xZnxTe is reviewed from the viewpoint of large diameter single crystal growth. A VGF method based on a multiple-zone furnace has been developed to grow 〈111〉-oriented 100 mm diameter single crystals. By this method, 〈111〉-oriented Cd1 − xZnxTe single crystals can be reproducibly grown. The grown crystals were characterized by the etch pit density measurement, X-ray diffractometry, GD-MS, photoluminescence, Hall measurement and precipitate observation. The growth mechanism is discussed on the basis of the transient solidification.
Physica status solidi, Jul 1, 2000
(a), T. Asahi (a), M. Hanafusa (a), A. Noda (a), A. Arakawa (a), M. Uchida (a), O. Oda (a), Y. Ya... more (a), T. Asahi (a), M. Hanafusa (a), A. Noda (a), A. Arakawa (a), M. Uchida (a), O. Oda (a), Y. Yamada (b), and T. Taguchi (b)
Fe doping and preparation of semi insulating InP by wafer annealing under Fe phosphide vapor pressure
Semi-insulating (SI) InP has been industrially produced by doping Fe atoms as deep acceptors. Fe ... more Semi-insulating (SI) InP has been industrially produced by doping Fe atoms as deep acceptors. Fe concentrations in InP are, however, largely varied from top to tail along the crystal growth axis because of impurity segregation. In the present work, we have examined the possibility of vapor phase doping for producing 50 mm diameter SI InP wafers with constant Fe concentrations by using a wafer annealing procedure. Small amount of Fe was charged with red phosphorus in ampoules in which InP wafers were annealed. It was found that the vapor phase doping is effective for Fe doping in InP. The present technology can be applied for the production of low Fe doped SI InP wafers with the same Fe concentration for all wafers from one InP ingot.
Efficient Method for Estimating Random Errors in Optical Constants Measured with THz-TDS
Conference on Lasers and Electro-Optics 2010, 2010
ABSTRACT