Y. Nanishi - Academia.edu (original) (raw)

Papers by Y. Nanishi

Journal of the Japanese Association for Crystal Growth, 2003

2012 IEEE 11th International Conference on Solid-State and Integrated Circuit Technology, 2012

New RF-MBE growth method called DERI (Droplet Elimination by Radical Beam Irradiation) was propos... more New RF-MBE growth method called DERI (Droplet Elimination by Radical Beam Irradiation) was proposed as a reproducible growth method of high quality and smooth InN films. Growth process was investigated based on in situ monitoring by RHEED and laser beam reflection. It was suggested that growth proceeds keeping two mono-layers of In and additional In droplets on the growing surface. Growth of InGaN alloy was also investigated, which showed strong segregation of Ga and In from In/Ga wetting layers. Using this phenomenon, high quality InN/InGaN, InGaN/InGaN MQWs were successfully fabricated. Possible new approach to passivate dislocation effect is proposed, which may give break through to obtain thick InGaN used for high efficiency solar cells.

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2004

... The result agrees well with recent articles, suggesting the effect of the Burstein–Moss shift... more ... The result agrees well with recent articles, suggesting the effect of the Burstein–Moss shift in ... angular distribution in the c plane (twist distribution) and high density of threading dislocations The dislocation density is on the order of and edge component dislocations ...

AIP Conference Proceedings, 2007

We report on an investigation of superconductivity in n-type InN. There is an optimum carrier den... more We report on an investigation of superconductivity in n-type InN. There is an optimum carrier density for the occurrence of the superconductivity. The lowest carrier density is limited by the Mott transition of ne~2×1017cm-3 and the highest density is limited by the superconductor to metal transition of ne~5×1020cm-3. As in the layered cuprate high Tc superconductors, the vortex solid of

SPIE Proceedings, 2009

ABSTRACT Position controlled InN nanocolumns were fabricated by electron-cyclotron-resonance plas... more ABSTRACT Position controlled InN nanocolumns were fabricated by electron-cyclotron-resonance plasma-excited molecular beam epitaxy (ECR-MBE) on hole-patterned GaN template by focused ion beam (FIB). Dependences of morphological changes in InN nanocolumn on V/III ratio and hole size were investigated. It is found that growth with a higher V/III ratio and a larger hole size resulted in the multiple formation of InN nanocolumns in one hole. By varying the hole density on the GaN template, we succeeded to change the density of InN nanocolumn by one order of magnitude from about 100/mum2 to 9/mum2. InN nanocolumn showed luminescence with peak energy of 0.74 eV by cathodoluminescence measurement.

International Meeting for Future of Electron Devices, 2004.

ABSTRACT

MRS Proceedings, 2004

ABSTRACTThe behavior of the E2 and A1(LO) optical phonons in Inx Ga1-x N has been analyzed by Ram... more ABSTRACTThe behavior of the E2 and A1(LO) optical phonons in Inx Ga1-x N has been analyzed by Raman scattering over the whole composition range. The frequencies of the E2 and A1(LO) modes decrease with increasing InN fraction. These modes display a significant broadening for an InN fraction of ≈ 60% and their linewidth decreases towards both ends of the composition range as a consequence of reduced cation disorder. Our results show a one-mode behavior for both E2 and A1(LO) modes of InGaN.

Gallium Nitride Materials and Devices VIII, 2013

We proposed recently a new RF-MBE method called droplet elimination by radical-beam irradiation (... more We proposed recently a new RF-MBE method called droplet elimination by radical-beam irradiation (DERI) for growing high-quality InN-based III-nitride films. DERI consists of two growth processes: a metal-rich growth process (MRGP) and a droplet elimination process (DEP). In InGaN growth, Ga was preferentially and selectively captured from the Ga/In wetting layer and droplets during MRGP. Then, excess In was swept out from the growing InGaN surface. The swept In was transformed to InN, epitaxially grown on top of InGaN during DEP using nitrogen radical beam irradiation. By repeating this process, an InN/InGaN MQW structure was successfully fabricated. Thick and uniform InGaN films were also successfully obtained by additionally irradiating the same Ga beam flux as that in MRGP even during DEP. When the irradiated Ga/N* beam flux ratio in DEP was changed from that in MRGP, an InxGa1-xN/InyGa1-yN MQW structure was successfully fabricated.

Gallium Nitride Materials and Devices Viii, 2013

We demonstrate light color conversion in patterned InGaN light-emitting diodes (LEDs), which is e... more We demonstrate light color conversion in patterned InGaN light-emitting diodes (LEDs), which is enhanced via non-radiative exciton resonant energy transfer (RET) from the electrically driven diode to colloidal semiconductor nanocrystals (NCs). Patterning of the diode is essential for the coupling between a quantum well (QW) and NCs, because the distance between the QW and NCs is a main and very critical factor of RET. Moreover, a proper design of the pattern can enhance light extraction.

Physical Review B, 2002

Infrared spectroscopic ellipsometry and micro-Raman scattering are used to study vibrational and ... more Infrared spectroscopic ellipsometry and micro-Raman scattering are used to study vibrational and electronic properties of high-quality hexagonal InN. The 0.22-m-thick highly n-conductive InN film was grown on c-plane sapphire by radio-frequency molecular-beam epitaxy. Combining our results from the ellipsometry data analysis with Hall-effect measurements, the isotropically averaged effective electron mass in InN is determined as 0.14m 0. The resonantly excited zone center E 1 ͑TO͒ phonon mode is observed at 477 cm Ϫ1 in the ellipsometry spectra. Despite the high electron concentration in the film, a strong Raman mode occurs in the spectral range of the unscreened A 1 (LO) phonon. Because an extended carrier-depleted region at the sample surface can be excluded from the ellipsometry-model analysis, we assign this mode to the lower branch of the large-wave-vector LO-phonon-plasmon coupled modes arising from nonconserving wave-vector scattering processes. The spectral position of this mode at 590 cm Ϫ1 constitutes a lower limit for the unscreened A 1 (LO) phonon frequency.

InN films were grown on (0001) sapphire substrates by radio-frequency plasma-excited molecular be... more InN films were grown on (0001) sapphire substrates by radio-frequency plasma-excited molecular beam epitaxy. Even without the initial growth processing, which includes substrate nitridation and buffer layer deposition, the c-axis orientation in InN films was well controlled by increasing the growth temperature but keeping the temperature below the InN dissociation temperature. However, without initial growth processing, the a-axis orientation in InN films tended to have various rotation domains within the c-plane. Hence, the initial growth processes of substrate nitridation and buffer layer deposition were useful and effective ways to control the rotation domains.

Physical Review B, 2007

The surfaces of In-and N-polarity InN grown by molecular-beam epitaxy have been investigated usin... more The surfaces of In-and N-polarity InN grown by molecular-beam epitaxy have been investigated using core-level and valence band x-ray photoemission spectroscopy ͑XPS͒. From the ratio of the In and N core-level XPS signal intensities, the clean InN surfaces have been found to be terminated by In adlayers, in agreement with the predictions of previous first-principles calculations. The In-and N-polarity surfaces are terminated by ϳ3.4 and ϳ2.0 ML of In, in each case 1 ML more than for Ga on GaN surfaces under metal-rich growth conditions. The valence band XPS indicates a valence band maximum to surface Fermi level separation of 1.32± 0.10 eV for both In-and N-polarity InN surfaces, indicating that the surface space charge is independent of polarity and, unlike for GaN, is not significantly affected by spontaneous polarization. This is due to the In coverage on the surface of InN of both polarities being sufficient to efficiently screen the polarization charge.

physica status solidi (c), 2003

Structural properties of InN films grown on (0001) sapphire by radio frequency molecular beam epi... more Structural properties of InN films grown on (0001) sapphire by radio frequency molecular beam epitaxy were characterized using transmission electron microscopy. A high density of threading dislocations was observed in the InN films. The density of the dislocation was more than 2 × 1010 cm−2. Most threading dislocations were edge-type dislocations. A columnar structure of crystallites with a small angular distribution in the c-plane (twist) was clearly observed. X-ray rocking curve measurements showed that InN film had relatively large distribution of twist in contrast to that of tilt. Convergent beam electron diffraction method was used to determine the polarity of the InN film. It is found that the InN film grown on the sapphire (0001) substrate showed N-polarity. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

physica status solidi (c), 2003

Page 1. phys. stat. sol. (c) 0, No. 6, 1750–1769 (2003) / DOI 10.1002/pssc.200303135 © 2003 WILEY... more Page 1. phys. stat. sol. (c) 0, No. 6, 1750–1769 (2003) / DOI 10.1002/pssc.200303135 © 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Phonons and free-carrier properties of binary, ternary, and quaternary group-III ...

physica status solidi (a), 2011

Photoluminescence (PL) properties are reported for a set of m-plane GaN films with Mg doping vari... more Photoluminescence (PL) properties are reported for a set of m-plane GaN films with Mg doping varied from mid 10 18 cm-3 to well above 10 19 cm-3. The samples were grown with MOCVD at reduced pressure on low defect density m-plane bulk GaN templates. The sharp line near bandgap bound exciton (BE) spectra observed below 50 K, as well as the broader donor-acceptor pair (DAP) PL bands at 2.9 eV to 3.3 eV give evidence of several Mg related acceptors, similar to the case of c-plane GaN. The dependence of the low temperature BE spectra on excitation intensity as well as the transient decay behavior demonstrate acoustic phonon assisted transfer between the acceptor BE states. The lower energy donor-acceptor pair spectra suggest the presence of deep acceptors, in addition to the two main shallower ones at about 0.23 eV. Similar spectra from Mg-doped GaN nanowires (NWs) grown by MOCVD are also demonstrated and briefly discussed.

Journal of Physics: Condensed Matter, 2009

We use a hydrodynamical approach to analyse the long-wavelength LO-phonon-plasmon coupled modes o... more We use a hydrodynamical approach to analyse the long-wavelength LO-phonon-plasmon coupled modes observed in a set of high-quality MBE-grown InN epilayers with electron densities varying over one order of magnitude, from ∼2 × 10(18) to ∼2 × 10(19) cm(-3). The samples were characterized by scanning electron microscopy, x-ray diffraction and Hall measurements. The correlation observed between the E(2)(high) mode frequency, and hence residual strain, and the electron density measured in the layers indicates that the differences in background electron density may be associated with threading dislocations. Owing to the low Raman signal, only the L(-) branch of the coupled modes can be unambiguously observed. The frequency of the L(-) Raman peak is, however, sensitive enough to the free electron density to allow its determination from lineshape fits to the spectra. These were carried out using an extended hydrodynamical model. Given the small bandgap energy and large conduction band nonparabolicity of InN, suitable expressions for the optical effective mass and mean square velocity that enter the hydrodynamical model were derived. Electron density values extracted from L(-) lineshape fits agree reasonably well with Hall determinations.

Journal of Electronic Materials, 2007

In-rich In x Al 1-x N films (0.47 £ x £ 1) were grown directly on nitridated (0001) sapphire subs... more In-rich In x Al 1-x N films (0.47 £ x £ 1) were grown directly on nitridated (0001) sapphire substrates without employing a buffer layer by radiofrequency molecular-beam epitaxy. Both photoluminescence peak energy and optical absorption-edge energy of the In x Al 1-x N films decreased monotonically with increasing In composition, which was consistent with the recently reported InN bandgap energies of~0.7 eV. The bowing parameter of this alloy was estimated to lie between 2.9 eV and 6.2 eV. Substrate nitridation with lower temperature and longer period conditions not only reduced misoriented In x Al 1-x N phases remarkably but also produced narrower tilt distribution in the c-axis-oriented In x Al 1-x N matrix.

Journal of The Electrochemical Society, 1981

Journal of the Japanese Association for Crystal Growth, 2003

2012 IEEE 11th International Conference on Solid-State and Integrated Circuit Technology, 2012

New RF-MBE growth method called DERI (Droplet Elimination by Radical Beam Irradiation) was propos... more New RF-MBE growth method called DERI (Droplet Elimination by Radical Beam Irradiation) was proposed as a reproducible growth method of high quality and smooth InN films. Growth process was investigated based on in situ monitoring by RHEED and laser beam reflection. It was suggested that growth proceeds keeping two mono-layers of In and additional In droplets on the growing surface. Growth of InGaN alloy was also investigated, which showed strong segregation of Ga and In from In/Ga wetting layers. Using this phenomenon, high quality InN/InGaN, InGaN/InGaN MQWs were successfully fabricated. Possible new approach to passivate dislocation effect is proposed, which may give break through to obtain thick InGaN used for high efficiency solar cells.

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2004

... The result agrees well with recent articles, suggesting the effect of the Burstein–Moss shift... more ... The result agrees well with recent articles, suggesting the effect of the Burstein–Moss shift in ... angular distribution in the c plane (twist distribution) and high density of threading dislocations The dislocation density is on the order of and edge component dislocations ...

AIP Conference Proceedings, 2007

We report on an investigation of superconductivity in n-type InN. There is an optimum carrier den... more We report on an investigation of superconductivity in n-type InN. There is an optimum carrier density for the occurrence of the superconductivity. The lowest carrier density is limited by the Mott transition of ne~2×1017cm-3 and the highest density is limited by the superconductor to metal transition of ne~5×1020cm-3. As in the layered cuprate high Tc superconductors, the vortex solid of

SPIE Proceedings, 2009

ABSTRACT Position controlled InN nanocolumns were fabricated by electron-cyclotron-resonance plas... more ABSTRACT Position controlled InN nanocolumns were fabricated by electron-cyclotron-resonance plasma-excited molecular beam epitaxy (ECR-MBE) on hole-patterned GaN template by focused ion beam (FIB). Dependences of morphological changes in InN nanocolumn on V/III ratio and hole size were investigated. It is found that growth with a higher V/III ratio and a larger hole size resulted in the multiple formation of InN nanocolumns in one hole. By varying the hole density on the GaN template, we succeeded to change the density of InN nanocolumn by one order of magnitude from about 100/mum2 to 9/mum2. InN nanocolumn showed luminescence with peak energy of 0.74 eV by cathodoluminescence measurement.

International Meeting for Future of Electron Devices, 2004.

ABSTRACT

MRS Proceedings, 2004

ABSTRACTThe behavior of the E2 and A1(LO) optical phonons in Inx Ga1-x N has been analyzed by Ram... more ABSTRACTThe behavior of the E2 and A1(LO) optical phonons in Inx Ga1-x N has been analyzed by Raman scattering over the whole composition range. The frequencies of the E2 and A1(LO) modes decrease with increasing InN fraction. These modes display a significant broadening for an InN fraction of ≈ 60% and their linewidth decreases towards both ends of the composition range as a consequence of reduced cation disorder. Our results show a one-mode behavior for both E2 and A1(LO) modes of InGaN.

Gallium Nitride Materials and Devices VIII, 2013

We proposed recently a new RF-MBE method called droplet elimination by radical-beam irradiation (... more We proposed recently a new RF-MBE method called droplet elimination by radical-beam irradiation (DERI) for growing high-quality InN-based III-nitride films. DERI consists of two growth processes: a metal-rich growth process (MRGP) and a droplet elimination process (DEP). In InGaN growth, Ga was preferentially and selectively captured from the Ga/In wetting layer and droplets during MRGP. Then, excess In was swept out from the growing InGaN surface. The swept In was transformed to InN, epitaxially grown on top of InGaN during DEP using nitrogen radical beam irradiation. By repeating this process, an InN/InGaN MQW structure was successfully fabricated. Thick and uniform InGaN films were also successfully obtained by additionally irradiating the same Ga beam flux as that in MRGP even during DEP. When the irradiated Ga/N* beam flux ratio in DEP was changed from that in MRGP, an InxGa1-xN/InyGa1-yN MQW structure was successfully fabricated.

Gallium Nitride Materials and Devices Viii, 2013

We demonstrate light color conversion in patterned InGaN light-emitting diodes (LEDs), which is e... more We demonstrate light color conversion in patterned InGaN light-emitting diodes (LEDs), which is enhanced via non-radiative exciton resonant energy transfer (RET) from the electrically driven diode to colloidal semiconductor nanocrystals (NCs). Patterning of the diode is essential for the coupling between a quantum well (QW) and NCs, because the distance between the QW and NCs is a main and very critical factor of RET. Moreover, a proper design of the pattern can enhance light extraction.

Physical Review B, 2002

Infrared spectroscopic ellipsometry and micro-Raman scattering are used to study vibrational and ... more Infrared spectroscopic ellipsometry and micro-Raman scattering are used to study vibrational and electronic properties of high-quality hexagonal InN. The 0.22-m-thick highly n-conductive InN film was grown on c-plane sapphire by radio-frequency molecular-beam epitaxy. Combining our results from the ellipsometry data analysis with Hall-effect measurements, the isotropically averaged effective electron mass in InN is determined as 0.14m 0. The resonantly excited zone center E 1 ͑TO͒ phonon mode is observed at 477 cm Ϫ1 in the ellipsometry spectra. Despite the high electron concentration in the film, a strong Raman mode occurs in the spectral range of the unscreened A 1 (LO) phonon. Because an extended carrier-depleted region at the sample surface can be excluded from the ellipsometry-model analysis, we assign this mode to the lower branch of the large-wave-vector LO-phonon-plasmon coupled modes arising from nonconserving wave-vector scattering processes. The spectral position of this mode at 590 cm Ϫ1 constitutes a lower limit for the unscreened A 1 (LO) phonon frequency.

InN films were grown on (0001) sapphire substrates by radio-frequency plasma-excited molecular be... more InN films were grown on (0001) sapphire substrates by radio-frequency plasma-excited molecular beam epitaxy. Even without the initial growth processing, which includes substrate nitridation and buffer layer deposition, the c-axis orientation in InN films was well controlled by increasing the growth temperature but keeping the temperature below the InN dissociation temperature. However, without initial growth processing, the a-axis orientation in InN films tended to have various rotation domains within the c-plane. Hence, the initial growth processes of substrate nitridation and buffer layer deposition were useful and effective ways to control the rotation domains.

Physical Review B, 2007

The surfaces of In-and N-polarity InN grown by molecular-beam epitaxy have been investigated usin... more The surfaces of In-and N-polarity InN grown by molecular-beam epitaxy have been investigated using core-level and valence band x-ray photoemission spectroscopy ͑XPS͒. From the ratio of the In and N core-level XPS signal intensities, the clean InN surfaces have been found to be terminated by In adlayers, in agreement with the predictions of previous first-principles calculations. The In-and N-polarity surfaces are terminated by ϳ3.4 and ϳ2.0 ML of In, in each case 1 ML more than for Ga on GaN surfaces under metal-rich growth conditions. The valence band XPS indicates a valence band maximum to surface Fermi level separation of 1.32± 0.10 eV for both In-and N-polarity InN surfaces, indicating that the surface space charge is independent of polarity and, unlike for GaN, is not significantly affected by spontaneous polarization. This is due to the In coverage on the surface of InN of both polarities being sufficient to efficiently screen the polarization charge.

physica status solidi (c), 2003

Structural properties of InN films grown on (0001) sapphire by radio frequency molecular beam epi... more Structural properties of InN films grown on (0001) sapphire by radio frequency molecular beam epitaxy were characterized using transmission electron microscopy. A high density of threading dislocations was observed in the InN films. The density of the dislocation was more than 2 × 1010 cm−2. Most threading dislocations were edge-type dislocations. A columnar structure of crystallites with a small angular distribution in the c-plane (twist) was clearly observed. X-ray rocking curve measurements showed that InN film had relatively large distribution of twist in contrast to that of tilt. Convergent beam electron diffraction method was used to determine the polarity of the InN film. It is found that the InN film grown on the sapphire (0001) substrate showed N-polarity. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

physica status solidi (c), 2003

Page 1. phys. stat. sol. (c) 0, No. 6, 1750–1769 (2003) / DOI 10.1002/pssc.200303135 © 2003 WILEY... more Page 1. phys. stat. sol. (c) 0, No. 6, 1750–1769 (2003) / DOI 10.1002/pssc.200303135 © 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Phonons and free-carrier properties of binary, ternary, and quaternary group-III ...

physica status solidi (a), 2011

Photoluminescence (PL) properties are reported for a set of m-plane GaN films with Mg doping vari... more Photoluminescence (PL) properties are reported for a set of m-plane GaN films with Mg doping varied from mid 10 18 cm-3 to well above 10 19 cm-3. The samples were grown with MOCVD at reduced pressure on low defect density m-plane bulk GaN templates. The sharp line near bandgap bound exciton (BE) spectra observed below 50 K, as well as the broader donor-acceptor pair (DAP) PL bands at 2.9 eV to 3.3 eV give evidence of several Mg related acceptors, similar to the case of c-plane GaN. The dependence of the low temperature BE spectra on excitation intensity as well as the transient decay behavior demonstrate acoustic phonon assisted transfer between the acceptor BE states. The lower energy donor-acceptor pair spectra suggest the presence of deep acceptors, in addition to the two main shallower ones at about 0.23 eV. Similar spectra from Mg-doped GaN nanowires (NWs) grown by MOCVD are also demonstrated and briefly discussed.

Journal of Physics: Condensed Matter, 2009

We use a hydrodynamical approach to analyse the long-wavelength LO-phonon-plasmon coupled modes o... more We use a hydrodynamical approach to analyse the long-wavelength LO-phonon-plasmon coupled modes observed in a set of high-quality MBE-grown InN epilayers with electron densities varying over one order of magnitude, from ∼2 × 10(18) to ∼2 × 10(19) cm(-3). The samples were characterized by scanning electron microscopy, x-ray diffraction and Hall measurements. The correlation observed between the E(2)(high) mode frequency, and hence residual strain, and the electron density measured in the layers indicates that the differences in background electron density may be associated with threading dislocations. Owing to the low Raman signal, only the L(-) branch of the coupled modes can be unambiguously observed. The frequency of the L(-) Raman peak is, however, sensitive enough to the free electron density to allow its determination from lineshape fits to the spectra. These were carried out using an extended hydrodynamical model. Given the small bandgap energy and large conduction band nonparabolicity of InN, suitable expressions for the optical effective mass and mean square velocity that enter the hydrodynamical model were derived. Electron density values extracted from L(-) lineshape fits agree reasonably well with Hall determinations.

Journal of Electronic Materials, 2007

In-rich In x Al 1-x N films (0.47 £ x £ 1) were grown directly on nitridated (0001) sapphire subs... more In-rich In x Al 1-x N films (0.47 £ x £ 1) were grown directly on nitridated (0001) sapphire substrates without employing a buffer layer by radiofrequency molecular-beam epitaxy. Both photoluminescence peak energy and optical absorption-edge energy of the In x Al 1-x N films decreased monotonically with increasing In composition, which was consistent with the recently reported InN bandgap energies of~0.7 eV. The bowing parameter of this alloy was estimated to lie between 2.9 eV and 6.2 eV. Substrate nitridation with lower temperature and longer period conditions not only reduced misoriented In x Al 1-x N phases remarkably but also produced narrower tilt distribution in the c-axis-oriented In x Al 1-x N matrix.

Journal of The Electrochemical Society, 1981