Takuji Hosoi - Academia.edu (original) (raw)

Papers by Takuji Hosoi

Research paper thumbnail of High-temperature CO2 treatment for improving electrical characteristics of 4H-SiC(0001) metal-oxide-semiconductor devices

Research paper thumbnail of Toward the Super Temporal Resolution Image Sensor with a Germanium Photodiode for Visible Light

Sensors

The theoretical temporal resolution limit tT of a silicon photodiode (Si PD) is 11.1 ps. We call ... more The theoretical temporal resolution limit tT of a silicon photodiode (Si PD) is 11.1 ps. We call “super temporal resolution” the temporal resolution that is shorter than that limit. To achieve this resolution, Germanium is selected as a candidate material for the photodiode (Ge PD) for visible light since the absorption coefficient of Ge for the wavelength is several tens of times higher than that of Si, allowing a very thin PD. On the other hand, the saturation drift velocity of electrons in Ge is about 2/3 of that in Si. The ratio suggests an ultra-short propagation time of electrons in the Ge PD. However, the diffusion coefficient of electrons in Ge is four times higher than that of Si. Therefore, Monte Carlo simulations were applied to analyze the temporal resolution of the Ge PD. The estimated theoretical temporal resolution limit is 0.26 ps, while the practical limit is 1.41 ps. To achieve a super temporal resolution better than 11.1 ps, the driver circuit must operate at leas...

Research paper thumbnail of Evaluation of the Impact of Al Atoms on SiO2/ SiC Interface Property by Using 4H-SiC n+-Channel Junctionless MOSFET

Materials Science Forum

To investigate the impact of Al atoms on channel mobility at SiO2/SiC interface, we fabricated th... more To investigate the impact of Al atoms on channel mobility at SiO2/SiC interface, we fabricated the junctionless metal-oxide-semiconductor field-effect transistors (MOSFETs), in which thin n+-SiC epitaxial layers with and without Al+ ion implantation were used as a channel, and compared their electrical characteristics. The effective mobility (meff) of n+-channel junctionless MOSFET without Al doping was estimated to be 14.9 cm2/Vs, which is higher than inversion-mode MOSFET fabricated with the same gate oxidation condition (3.1 cm2/Vs). The meff values of the MOSFETs with low Al doping concentration (5´1017 and 1´1018 cm-3) were almost the same as that of Al-free MOSFET, and the device with the highest Al doping (5´1018 cm-3) exhibited slight mobility degradation of about 15% compared to the other devices. Hall mobility in thick n+ layer with the highest Al doping was also slightly degraded, suggesting that Al atoms in the channel are not the major cause of degraded SiO2/SiC interfa...

Research paper thumbnail of Controlled oxide interlayer for improving reliability of SiO2/GaN MOS devices

Japanese Journal of Applied Physics

The impact of controlling Ga-oxide (GaO x) interlayers in SiO 2 /GaO x /GaN gate stacks is invest... more The impact of controlling Ga-oxide (GaO x) interlayers in SiO 2 /GaO x /GaN gate stacks is investigated by means of physical and electrical characterizations. Direct deposition of SiO 2 insulators produces thin GaO x interlayers, and subsequent oxidation treatment attains high-quality insulator/GaN interface. However, the Ga diffusion into the SiO 2 layers severely degrades the breakdown characteristics of GaN-MOS devices. To improve reliability of such devices, we proposed a two-step procedure with the initial SiO 2 deposition conducted under nitrogen-rich ambient, followed by thick SiO 2 capping. We found that this two-step procedure enables nitrogen incorporation in the insulator/GaN interface to stabilize GaN surface. Consequently, the Ga diffusion into the SiO 2 overlayer during the oxidation annealing is effectively suppressed. The proposed method allows us to achieve a SiO 2 /GaO x /GaN stacked structure of superior electrical property with improved Weibull distribution of an oxide breakdown field and with interface state density below 10 10 cm −2 eV −1 .

Research paper thumbnail of Comparative study on thermal robustness of GaN and AlGaN/GaN MOS devices with thin oxide interlayers

Japanese Journal of Applied Physics

Similarities and differences in the design of the interfaces between gate dielectrics and GaN-bas... more Similarities and differences in the design of the interfaces between gate dielectrics and GaN-based semiconductors were systematically investigated with a focus on the thermal stability of the interlayers. Although the excellent electrical properties of a SiO 2 /GaN interface with a thin Ga-oxide interlayer (SiO 2 /GaO x /GaN) were deteriorated by high-temperature treatment at around 1000°C, the thin oxide on the AlGaN surface (SiO 2 /GaO x /AlGaN) exhibited superior thermal stability and interface quality even after treatment at 1000°C. Physical characterizations showed that thermal decomposition of the thin GaO x layer on the GaN surface is promoted by oxygen transfer, which produces volatile products, leading to remarkable roughening of the GaN surface. In contrast, decomposition of the thin GaO x layer was suppressed on the AlGaN surface under the high temperatures, preserving a smooth oxide surface. The mechanisms behind both the improved and degraded electrical properties in these GaNbased MOS structures are discussed on the basis of these findings.

Research paper thumbnail of Annealing behavior of open spaces in AlON films studied by monoenergetic positron beams

Research paper thumbnail of Insight into enhanced field-effect mobility of 4H-SiC MOSFET with Ba incorporation studied by Hall effect measurements

AIP Advances

Paper published as part of the special topic on Chemical Physics, Energy, Fluids and Plasmas, Mat... more Paper published as part of the special topic on Chemical Physics, Energy, Fluids and Plasmas, Materials Science and Mathematical Physics ARTICLES YOU MAY BE INTERESTED IN Characterization of SiO 2 /SiC interface states and channel mobility from MOSFET characteristics including variable-range hopping at cryogenic temperature AIP Advances 8, 045217 (2018);

Research paper thumbnail of Synchrotron radiation X-ray photoelectron spectroscopy of Ti/Al ohmic contacts to n-type GaN: Key role of Al capping layers in interface scavenging reactions

Applied Physics Express

View the article online for updates and enhancements.

Research paper thumbnail of Impact of Si Diffusion Barrier Layer Formed on TiN Surface by In Situ Oxygen Treatment Process for Advanced Gate-First Metal/High-k Stacks

Research paper thumbnail of Structure and Surface Morphology of Thermal SiO<sub>2</sub> Grown on 4H-SiC by Metal-Enhanced Oxidation Using Barium

Research paper thumbnail of Comparison of ordered structure in buried oxide layers in high-dose, low-dose, and internal-thermal-oxidation separation-by-implanted-oxygen wafers

Thin Solid Films

ABSTRACT The ordered SiO2 in the buried oxide (BOX) layer of high-dose, low-dose, and internal-th... more ABSTRACT The ordered SiO2 in the buried oxide (BOX) layer of high-dose, low-dose, and internal-thermal-oxidation (ITOX) separation-by-implanted-oxygen (SIMOX) wafers was investigated by X-ray diffraction. From the results, it was found that the SiO2 molecules in the low-dose and ITOX SIMOX wafers are better ordered than those in the high-dose SIMOX wafer and that the ordered structure of the ITOX layer is different from that of the originally formed BOX layer, suggesting that the ITOX layer has a structure similar to that of the ordered SiO2 in the thermal oxide layer.

Research paper thumbnail of Ambient-Pressure XPS Study of GeO2/Ge(100) and SiO2/Si(100) at Controlled Relative Humidity

Research paper thumbnail of Ultrahigh-temperature rapid thermal oxidation of 4H-SiC(0001) surfaces and oxidation temperature dependence of SiO2/SiC interface properties

Research paper thumbnail of Structural Characterization of Very Thin Strained Si Layers by Synchrotron X-ray Topography

Research paper thumbnail of Insight into metal-enhanced oxidation using barium on 4H-SiC surfaces

Japanese Journal of Applied Physics

Research paper thumbnail of Effect of nitrogen incorporation into Al-based gate insulators in AlON/AlGaN/GaN metal–oxide–semiconductor structures

Research paper thumbnail of Schottky barrier height modulation at NiGe/Ge interface by phosphorous ion implantation and its application to Ge-based CMOS devices

2015 15th International Workshop on Junction Technology (IWJT), 2015

Research paper thumbnail of Characterization of Sb-Doped Fully-Silicided NiSi/SiO 2 /Si MOS Structure

X-ray photoelectron spectroscopy (XPS) measurement of Sb-doped fully-silicided (FUSI) NiSi/SiO2 i... more X-ray photoelectron spectroscopy (XPS) measurement of Sb-doped fully-silicided (FUSI) NiSi/SiO2 interface has been carried out to evaluate location of Sb pileup and to discuss its role for workfunction shift. The XPS result revealed Sb encroachment into SiO2. Workfunction characterization by XPS implied that NiSi workfunction was identical to its original value without Sb pileup located inside the gate oxide. The

Research paper thumbnail of Origin of flatband voltage shift and unusual minority carrier generation in thermally grown Ge02/Ge metal-oxide-semiconductor devices

Applied Physics Letters, 2009

Improvement in electrical properties of thermally grown GeO2/Ge metal-oxide-semiconductor (MOS) c... more Improvement in electrical properties of thermally grown GeO2/Ge metal-oxide-semiconductor (MOS) capacitors, such as significantly reduced flatband voltage (VFB) shift, small hysteresis, and minimized minority carrier response in capacitance-voltage (C-V) characteristics, has been demonstrated by in situ low temperature vacuum annealing prior to gate electrode deposition. Thermal desorption analysis has revealed that not only water but also hydrocarbons are easily infiltrated into GeO2 layers during air exposure and desorbed at around 300 °C, indicating that organic molecules within GeO2/Ge MOS structures are possible origins of electrical defects. The inversion capacitance, indicative of minority carrier generation, increases with air exposure time for Au/GeO2/Ge MOS capacitors, while maintaining an interface state density (Dit) of about a few 1011 cm-2 eV-1. Unusual increase in inversion capacitance was found to be suppressed by Al2O3 capping (Au/Al2O3/GeO2/Ge structures). This suggests that electrical defects induced outside the Au electrode by infiltrated molecules may enhance the minority carrier generation, and thus acting as a minority carrier source just like MOS field-effect transistors.

Research paper thumbnail of Formation of epitaxially ordered SiO2 in oxygen-implanted silicon during thermal annealing

Journal of Crystal Growth, 2002

The growth of epitaxially ordered SiO 2 in oxygen-implanted silicon during thermal annealing was ... more The growth of epitaxially ordered SiO 2 in oxygen-implanted silicon during thermal annealing was investigated. The implanted Si wafers were annealed for various durations at 13501C. Diffraction streaks at 0.5 0.5 L (LB1) of Si were observed from these samples. The intensity of the streak gradually increased with annealing time, while the peak position and the width of the streak did not change. Referring to these results, the growth of the buried oxide layers is discussed in terms of the ordered structure.

Research paper thumbnail of High-temperature CO2 treatment for improving electrical characteristics of 4H-SiC(0001) metal-oxide-semiconductor devices

Research paper thumbnail of Toward the Super Temporal Resolution Image Sensor with a Germanium Photodiode for Visible Light

Sensors

The theoretical temporal resolution limit tT of a silicon photodiode (Si PD) is 11.1 ps. We call ... more The theoretical temporal resolution limit tT of a silicon photodiode (Si PD) is 11.1 ps. We call “super temporal resolution” the temporal resolution that is shorter than that limit. To achieve this resolution, Germanium is selected as a candidate material for the photodiode (Ge PD) for visible light since the absorption coefficient of Ge for the wavelength is several tens of times higher than that of Si, allowing a very thin PD. On the other hand, the saturation drift velocity of electrons in Ge is about 2/3 of that in Si. The ratio suggests an ultra-short propagation time of electrons in the Ge PD. However, the diffusion coefficient of electrons in Ge is four times higher than that of Si. Therefore, Monte Carlo simulations were applied to analyze the temporal resolution of the Ge PD. The estimated theoretical temporal resolution limit is 0.26 ps, while the practical limit is 1.41 ps. To achieve a super temporal resolution better than 11.1 ps, the driver circuit must operate at leas...

Research paper thumbnail of Evaluation of the Impact of Al Atoms on SiO2/ SiC Interface Property by Using 4H-SiC n+-Channel Junctionless MOSFET

Materials Science Forum

To investigate the impact of Al atoms on channel mobility at SiO2/SiC interface, we fabricated th... more To investigate the impact of Al atoms on channel mobility at SiO2/SiC interface, we fabricated the junctionless metal-oxide-semiconductor field-effect transistors (MOSFETs), in which thin n+-SiC epitaxial layers with and without Al+ ion implantation were used as a channel, and compared their electrical characteristics. The effective mobility (meff) of n+-channel junctionless MOSFET without Al doping was estimated to be 14.9 cm2/Vs, which is higher than inversion-mode MOSFET fabricated with the same gate oxidation condition (3.1 cm2/Vs). The meff values of the MOSFETs with low Al doping concentration (5´1017 and 1´1018 cm-3) were almost the same as that of Al-free MOSFET, and the device with the highest Al doping (5´1018 cm-3) exhibited slight mobility degradation of about 15% compared to the other devices. Hall mobility in thick n+ layer with the highest Al doping was also slightly degraded, suggesting that Al atoms in the channel are not the major cause of degraded SiO2/SiC interfa...

Research paper thumbnail of Controlled oxide interlayer for improving reliability of SiO2/GaN MOS devices

Japanese Journal of Applied Physics

The impact of controlling Ga-oxide (GaO x) interlayers in SiO 2 /GaO x /GaN gate stacks is invest... more The impact of controlling Ga-oxide (GaO x) interlayers in SiO 2 /GaO x /GaN gate stacks is investigated by means of physical and electrical characterizations. Direct deposition of SiO 2 insulators produces thin GaO x interlayers, and subsequent oxidation treatment attains high-quality insulator/GaN interface. However, the Ga diffusion into the SiO 2 layers severely degrades the breakdown characteristics of GaN-MOS devices. To improve reliability of such devices, we proposed a two-step procedure with the initial SiO 2 deposition conducted under nitrogen-rich ambient, followed by thick SiO 2 capping. We found that this two-step procedure enables nitrogen incorporation in the insulator/GaN interface to stabilize GaN surface. Consequently, the Ga diffusion into the SiO 2 overlayer during the oxidation annealing is effectively suppressed. The proposed method allows us to achieve a SiO 2 /GaO x /GaN stacked structure of superior electrical property with improved Weibull distribution of an oxide breakdown field and with interface state density below 10 10 cm −2 eV −1 .

Research paper thumbnail of Comparative study on thermal robustness of GaN and AlGaN/GaN MOS devices with thin oxide interlayers

Japanese Journal of Applied Physics

Similarities and differences in the design of the interfaces between gate dielectrics and GaN-bas... more Similarities and differences in the design of the interfaces between gate dielectrics and GaN-based semiconductors were systematically investigated with a focus on the thermal stability of the interlayers. Although the excellent electrical properties of a SiO 2 /GaN interface with a thin Ga-oxide interlayer (SiO 2 /GaO x /GaN) were deteriorated by high-temperature treatment at around 1000°C, the thin oxide on the AlGaN surface (SiO 2 /GaO x /AlGaN) exhibited superior thermal stability and interface quality even after treatment at 1000°C. Physical characterizations showed that thermal decomposition of the thin GaO x layer on the GaN surface is promoted by oxygen transfer, which produces volatile products, leading to remarkable roughening of the GaN surface. In contrast, decomposition of the thin GaO x layer was suppressed on the AlGaN surface under the high temperatures, preserving a smooth oxide surface. The mechanisms behind both the improved and degraded electrical properties in these GaNbased MOS structures are discussed on the basis of these findings.

Research paper thumbnail of Annealing behavior of open spaces in AlON films studied by monoenergetic positron beams

Research paper thumbnail of Insight into enhanced field-effect mobility of 4H-SiC MOSFET with Ba incorporation studied by Hall effect measurements

AIP Advances

Paper published as part of the special topic on Chemical Physics, Energy, Fluids and Plasmas, Mat... more Paper published as part of the special topic on Chemical Physics, Energy, Fluids and Plasmas, Materials Science and Mathematical Physics ARTICLES YOU MAY BE INTERESTED IN Characterization of SiO 2 /SiC interface states and channel mobility from MOSFET characteristics including variable-range hopping at cryogenic temperature AIP Advances 8, 045217 (2018);

Research paper thumbnail of Synchrotron radiation X-ray photoelectron spectroscopy of Ti/Al ohmic contacts to n-type GaN: Key role of Al capping layers in interface scavenging reactions

Applied Physics Express

View the article online for updates and enhancements.

Research paper thumbnail of Impact of Si Diffusion Barrier Layer Formed on TiN Surface by In Situ Oxygen Treatment Process for Advanced Gate-First Metal/High-k Stacks

Research paper thumbnail of Structure and Surface Morphology of Thermal SiO<sub>2</sub> Grown on 4H-SiC by Metal-Enhanced Oxidation Using Barium

Research paper thumbnail of Comparison of ordered structure in buried oxide layers in high-dose, low-dose, and internal-thermal-oxidation separation-by-implanted-oxygen wafers

Thin Solid Films

ABSTRACT The ordered SiO2 in the buried oxide (BOX) layer of high-dose, low-dose, and internal-th... more ABSTRACT The ordered SiO2 in the buried oxide (BOX) layer of high-dose, low-dose, and internal-thermal-oxidation (ITOX) separation-by-implanted-oxygen (SIMOX) wafers was investigated by X-ray diffraction. From the results, it was found that the SiO2 molecules in the low-dose and ITOX SIMOX wafers are better ordered than those in the high-dose SIMOX wafer and that the ordered structure of the ITOX layer is different from that of the originally formed BOX layer, suggesting that the ITOX layer has a structure similar to that of the ordered SiO2 in the thermal oxide layer.

Research paper thumbnail of Ambient-Pressure XPS Study of GeO2/Ge(100) and SiO2/Si(100) at Controlled Relative Humidity

Research paper thumbnail of Ultrahigh-temperature rapid thermal oxidation of 4H-SiC(0001) surfaces and oxidation temperature dependence of SiO2/SiC interface properties

Research paper thumbnail of Structural Characterization of Very Thin Strained Si Layers by Synchrotron X-ray Topography

Research paper thumbnail of Insight into metal-enhanced oxidation using barium on 4H-SiC surfaces

Japanese Journal of Applied Physics

Research paper thumbnail of Effect of nitrogen incorporation into Al-based gate insulators in AlON/AlGaN/GaN metal–oxide–semiconductor structures

Research paper thumbnail of Schottky barrier height modulation at NiGe/Ge interface by phosphorous ion implantation and its application to Ge-based CMOS devices

2015 15th International Workshop on Junction Technology (IWJT), 2015

Research paper thumbnail of Characterization of Sb-Doped Fully-Silicided NiSi/SiO 2 /Si MOS Structure

X-ray photoelectron spectroscopy (XPS) measurement of Sb-doped fully-silicided (FUSI) NiSi/SiO2 i... more X-ray photoelectron spectroscopy (XPS) measurement of Sb-doped fully-silicided (FUSI) NiSi/SiO2 interface has been carried out to evaluate location of Sb pileup and to discuss its role for workfunction shift. The XPS result revealed Sb encroachment into SiO2. Workfunction characterization by XPS implied that NiSi workfunction was identical to its original value without Sb pileup located inside the gate oxide. The

Research paper thumbnail of Origin of flatband voltage shift and unusual minority carrier generation in thermally grown Ge02/Ge metal-oxide-semiconductor devices

Applied Physics Letters, 2009

Improvement in electrical properties of thermally grown GeO2/Ge metal-oxide-semiconductor (MOS) c... more Improvement in electrical properties of thermally grown GeO2/Ge metal-oxide-semiconductor (MOS) capacitors, such as significantly reduced flatband voltage (VFB) shift, small hysteresis, and minimized minority carrier response in capacitance-voltage (C-V) characteristics, has been demonstrated by in situ low temperature vacuum annealing prior to gate electrode deposition. Thermal desorption analysis has revealed that not only water but also hydrocarbons are easily infiltrated into GeO2 layers during air exposure and desorbed at around 300 °C, indicating that organic molecules within GeO2/Ge MOS structures are possible origins of electrical defects. The inversion capacitance, indicative of minority carrier generation, increases with air exposure time for Au/GeO2/Ge MOS capacitors, while maintaining an interface state density (Dit) of about a few 1011 cm-2 eV-1. Unusual increase in inversion capacitance was found to be suppressed by Al2O3 capping (Au/Al2O3/GeO2/Ge structures). This suggests that electrical defects induced outside the Au electrode by infiltrated molecules may enhance the minority carrier generation, and thus acting as a minority carrier source just like MOS field-effect transistors.

Research paper thumbnail of Formation of epitaxially ordered SiO2 in oxygen-implanted silicon during thermal annealing

Journal of Crystal Growth, 2002

The growth of epitaxially ordered SiO 2 in oxygen-implanted silicon during thermal annealing was ... more The growth of epitaxially ordered SiO 2 in oxygen-implanted silicon during thermal annealing was investigated. The implanted Si wafers were annealed for various durations at 13501C. Diffraction streaks at 0.5 0.5 L (LB1) of Si were observed from these samples. The intensity of the streak gradually increased with annealing time, while the peak position and the width of the streak did not change. Referring to these results, the growth of the buried oxide layers is discussed in terms of the ordered structure.