Gerhard Fasol

Gerhard Fasol
Eurotechnology Japan KK · CEO

PhD (Cambridge Univ. Trinity College)

About

120
Publications
4,728
Reads
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7,869
Citations
Citations since 2016
0 Research Items
1270 Citations
2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250
Introduction
Physicist and entrepreneur in Tokyo/Japan. Eurotechnology-Japan, CEO & Founder Kyushu University, Guest Professor Previously: -GMO Cloud KK, Board Director, Member of Supervisory & Audit Committee - tenured Faculty at Cambridge University - Director of Studies and Fellow at Trinity College, Cambridge - Assoc Professor at Tokyo University / Electrical Engineering Dept. - Leader of Sakigake project on spin-electronics of Japan's Science and Technology Agency (first non-Japanese to deliver results) - Manager of Hitachi Cambridge Lab in start-up phase - Invited Professor at Ecole Normale Superieure, Paris more: https://fasol.com/
Additional affiliations
April 2017 - present
Kyushu University
Position
  • Professor
September 1992 - September 1996
The University of Tokyo
Position
  • Professor (Associate)
September 1991 - September 1992
The University of Tokyo
Position
  • Professor (Associate)
Education
September 1978 - February 1982
University of Cambridge
Field of study
  • Physics

Publications

Publications (120)
Article
The motion, the excitations and the dielectric response of carriers parallel to the two-dimensional electron layers of modulation doped heterojunctions and multi-quantum wells are characterised by collective excitations (density oscillations = plasmons) and single particle excitations (acceleration of single electrons). These excitations correspond...
Article
The story of Shuji Nakamura and the blue laser diode is remarkable. It is clear from this book that he enjoys this fact and wishes his readers to become familiar with his success. Nakamura was a little known researcher at a small but successful Japanese company, Nichia Chemical, on Shikoku, one of Japan's four main islands. One of their successful...
Chapter
Japan ist die zweitgrößte Wirtschaftsnation der Welt — etwa 70% der Wirtschaft Asiens (inklusive China und Indien) ist in Japan. Damit ist Japan für viele deutsche Firmen der zweitgrößte Markt nach den USA, aber auch die zweitgrößte Heimat für echte oder potentielle Konkurrenten und/oder Partner. Durch kulturelle und sprachliche Unterschiede schein...
Article
An economical system for time-resolved photoluminescence spectroscopy has been constructed around a nitrogen laser pumped dye laser. The signal is detected by a photomultiplier in a liquid nitrogen cooled housing constructed for 5 ns response time and analysed by a boxcar detector modified to have low drift. The spectra are corrected for the respon...
Article
Luminescence in semiconducting amorphous phosphorus is resolved into a band (HE) centred near 1.4 eV and a band (LE) centred near 1.15 eV by time-resolved luminescence measurements excited by 6 ns dye laser pulses. LE decays with a time constant around 150 ns. It is interpreted to be due to recombination of a singlet exciton state corresponding to...
Article
The authors present results of spin-flip and non-spin-flip electronic Raman measurements on a GaAs with doping superlattice as a function of the non-equilibrium charge carrier concentration. They have been able to measure down to concentrations where only the lowest sub-band is appreciably populated. While the spin-flip excitation energies vary str...
Article
The author presents the dependence of the excitonic 'LE' band (near 1.15 eV) and the distant pair 'He' luminescence band of red amorphous phosphorus as a function of temperature and excitation energy. The LE band decreases rapidly with increasing temperature. Excited by 6 ns laser pulses HE luminescence can even be observed at room temperature, whi...
Chapter
In this chapter, the first successful CW operation of InGaN multi-quantumwell (MQW)-structure LDs at 233 K is described.
Chapter
As the melting point of GaN is approximately 1700 °C the growth of GaN crystals from a liquid melt is difficult and GaN is instead normally grown using the halide vapor phase epitaxy (HVPE) method using an equilibrium mixture of nitrogen and Ga-containing gas. In practice, this is achieved by depositing GaN on a sapphire crystal at 1000 °C using a...
Chapter
Ever since research into the GaN system began in the 1960s, the biggest unsolved problem has been the production of p-type GaN. For a long time it was impossible to obtain p-type GaN films. Unavailability of p-type GaN films has prevented III-V nitrides from yielding visible light emitting devices, such as blue LEDs and LDs. In 1989, Amano et al. s...
Chapter
During the 1980s lattice matching between epitaxial layer and substrate was said to be the most important point in heteroepitaxial growth. This section describes lattice matching. At the time of these discussions in the 1980s it was not often possible to achieve good crystal quality and so the devices were thought to have a short lifetime if a larg...
Chapter
The spectra of InGaN multi-quantum-well (MQW)-structure laser diodes (LDs) show several peaks with peak separations (1–5 meV) different than can be explained by the longitudinal mode spacing. It was proposed that these subband emissions resulted from transitions between quantum dot-like subband energy levels [336]. Recombination of localized excito...
Chapter
Superbright blue, green, and white InGaN SQW LEDs have been discussed in this book. By combining high-power, high-brightness blue InGaN SQW LEDs, green InGaN SQW LEDs, and red GaAlAs LEDs, many kinds of applications, such as LED full-color displays and LED white lamps for use in place of light bulbs or fluorescent lamps, are now possible with chara...
Chapter
The previous chapters of this book demonstrated the development of commercial Group-III-nitride based high-power blue (5 mW) and green (3 mW) LEDs [330, 331]. In order to obtain LEDs with such high-power emission in different spectal regions, an InGaN single-quantum-well (SQW) structure is used as the active layer. LEDs have a large range of applic...
Chapter
We will see in this chapter, how Zn-, and Si-co-doping together with other improvements can dramatically improve the output power and quantum efficiency. While Chap. 8 described the development of InGaN superlattice and double heterostructure based light emitting diodes in the 100 µW, 0.15% range, the present chapter will demonstrate the developmen...
Chapter
In the present chapter investigations into the emission mechanisms for light emitting diodes and lasers are discussed. We find the first evidence for proposing laser emission from excitons localized at local potential fluctuations. This concept will be further developed to explain the results also given in Chaps. 13 and 14.
Chapter
In order to use GaN for blue light emitting diodes (LEDs) and laser diodes (LDs) the long standing problem of high p-type doping had to be solved. Amano et al. [41, 153] grew Mg-doped GaN films using AlN buffer layers on a sapphire substrate. After growth, low-energy electron beam irradiation (LEEBI) treatment was performed on these GaN films and p...
Chapter
This chapter provides some background information to the main part of this book, the purpose of which is to introduce gallium nitride based light emitting diodes and lasers. While the other parts of this book are technical and mainly addressed to an audience of electrical engineers, scientists, researchers and physicists working in the field of gal...
Article
The authors demonstrate two applications of Raman scattering for the characterization of low-dimensional structures: they measure the plasmon properties of a modulation-doped multiple quantum well with multiple subband occupation by Raman scattering and hence determine the electronic subband structure and the subband occupation. Secondly, they repo...
Article
Continuous wave (CW) hot electron luminescence (HEL) spectra indicate that hot electrons scatter predominantly with cold electrons rather than with hot electrons or hot holes. Two series of experiments are compared. In the first series the sample is GaAs:Be. Increasing the concentration of optically injected carriers results in a widening distribut...
Article
Future developments in circuit design and magnetic data storage will demand smaller and smaller structures. In his Research Commentary, Fasol reviews recent methods for fabricating metallic and magnetic nanowires. In some cases, the precision of existing technology can be applied to creating tiny wires with useful properties.
Article
Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all branches of science and how science impacts upon all aspects of society and life.
Article
One year ago, researchers at Nichia Chemical Industries in Japan announced the development of a continuously operating laser diode that produced light emission at blue wavelengths. In his Perspective, Fasol describes the latest research from Nichia, in which a new blue laser architecture has been developed that promises continuous operation for 10,...
Article
In the present work, the coherent propagation of electrons is simulated by solving the time-dependent Schröinger Equation. The underlying purpose of the present work is the simulation, design and analysis of novel high speed electronic devices based on coherent electrons. Electron propagation through periodic lattices of limited size is calculated....
Article
Full-text available
A selective electrodeposition method for the fabrication of extremely thin and long metallic and magnetic wires is introduced. Growth is done on the cleaved edge of a semiconductor multilayer structure incorporating a 4-nm-wide modulation doped quantum well. This conducting quantum well is connected to the negative current contact during electrodep...
Article
Data communications relies as never before on high-performance lasers for generating the pulses that travel down optical fibers. In his Perspective, Fasol discusses a recently invented laser—the quantum-dot vertical-cavity surface-emitting laser. Made possible by breakthroughs in crystal growth, this laser operates at room temperature and may soon...
Chapter
As discussed in previous sections, recent research on III–V nitrides has paved the way for the realization of high-quality crystals of AlGaN and InGaN, and p-type conduction in AlGaN [300, 301, 302, 303, 304]. The hole-compensation mechanism of p-type AlGaN has also been elucidated [305, 306]. Highbrightness blue and blue-green light emitting diode...
Chapter
Blue laser diodes (LDs) are needed for a number of applications, including full-color electroluminescent displays, read—write laser sources for highdensity information storage on magnetic and optical media, and for undersea optical communications.
Chapter
During the 1980s lattice matching between epitaxial layer and substrate was said to be the most important point in heteroepitaxial growth. This section describes lattice matching. At the time of these discussions in the 1980s it was not often possible to achieve good crystal quality and so the devices were thought to have a short lifetime if a larg...
Chapter
Shuji Nakamura was born in Ehime, Japan on May 22, 1954. He received his B.E., M.S., and Ph.D. degrees in electronic engineering from the University of Tokushima, Japan, in 1977, 1979, and 1994, respectively. In 1979, he joined Nichia Chemical Industries Ltd. Since that time, he has studied optoelectronic materials (such as GaAs, GaP, and GaAlAs),...
Chapter
The present Chap. 9 shows, how Zn-, and Si-co-doping together with other improvements can dramatically improve the output power and quantum efficiency. While the previous Chap. 8 described the development of InGaN superlattice and double heterostructure based light emitting diodes in the 100 µW, 0.15% range, the present Chap. 9 will demonstrate the...
Chapter
As the melting point of GaN is approximately 1700°C the growth of GaN crystals from a liquid melt is difficult and GaN is instead normally grown using the halide vapor phase epitaxy (HVPE) method using an equilibrium mixture of nitrogen and Ga-containing gas. In practice, this is achieved by depositing GaN on a sapphire crystal at 1000°C using a mi...
Chapter
Wide-band-gap semiconducting GaN is a promising candidate for fabricating blue light emitting diodes (LEDs) and UV-emitting laser diodes (LDs). In order to realize the production of these emitting devices, a method for obtaining high-quality GaN films and highly p-type GaN films must be developed. It has been very difficult to obtain high-quality G...
Chapter
Gallium nitride and related compounds have been propelled from obscurity into the mainstream of physics and electrical engineering research within the time-span of a few months through Nakamura’s development of commercially viable blue and green light emitters.
Chapter
The light emitting diode (LED) could be considered the ultimate general source of continuous light due to its high luminescence efficiency, quick response time, and long lifetime. For example, the electrical efficiency of a standard ‘white’ light is almost halved if a color filter is employed to produce color, such as is the case for traffic signal...
Article
„Wir müssen in Zukunft mehr Erfindungen selber machen, Technologien selber erfinden”, fordert Professor Akito Arima, einer der einflußreichsten Wissenschaftler Japans. Seit Ende des Zweiten Weltkrieges hat sich Japan bewußt auf die effiziente Entwicklung von Produkten zu Lasten der Grundlagenforschung konzentriert. Professor Arima kämpfte lange Jah...
Article
Full-text available
In December 1995, a researcher at a medium-sized company in Japan announced the development of a long-sought device—a laser diode operating at room temperature that emits blue light. In his Perspective, Fasol describes the development of this device, which may have major applications in optical data storage and computer displays, and the corporate...
Article
Der „Tag der DPG” am 10. November 1995 im Physikzentrum Bad Honnef war wiederum, wie im Jahr zuvor, der Lage auf dem Arbeitsmarkt und dem künftigen Rollenverständnis der DPG gewidmet. Einführend berichtete DPG-Präsident H. G. Danielmeyer vom 2. Weltkongreß der Physikalischen Gesellschaften in Tokio Mitte September 1995 (siehe Einschub auf Seite 168...
Article
Until recently, most work in the area of mesoscopic devices and quantum wire transport has assumed the free-electron model, assuming non-interacting spin-free electrons. We introduce electron-electron interactions, electron spin and microscopic crystal properties into the design of experimental mesoscopic device structures. This work results in the...
Article
The internal potential seen by electrons within the quantum wire region of split-gate point contacts is determined using the thermal spread of the electron distribution function as an ''internal reference''. The determination of the internal potential is used to analyze the energy distribution of hot electrons propagating between two quantum point...
Chapter
The electron energy bands in a semiconductor quantum wire in general are expected to show a wave vector dependent spin splitting with terms proportional to k3. We show that the wave vector dependence gives rise to a strong asymmetry of the electron-electron pair scattering with respect to the spin subbands. We show that one consequence of this asym...
Article
We predict a new effect for transport in quantum wires: spontaneous spin polarization. Most work on transport in mesoscopic devices has assumed a model of non interacting, spin-free electrons. We introduce spin, electron pair scattering and microscopic crystal properties into the design of mesoscopic devices. The new spin polarization effect result...
Article
Full-text available
A microscopic picture of electron-electron pair scattering in single mode quantum wires is introduced which includes electron spin. A new source of excess noise for hot carriers is presented. We show that zero magnetic field spin splitting in quantum wires can lead to a dramatic spin-subband dependence of electron-electron scattering, including the...
Article
Full-text available
We show that a quantum‐wire device with spin splitting can work as an active spin polarizer. Hot electrons in one ‘‘spin’’ subband (e.g., ‘‘spin up’’) may pass such a device with weak electron pair scattering, while electrons in the opposite subband (‘‘spin down’’) may have high conversion probability into the spin‐up subband, resulting in spin pol...
Chapter
Compositionally modulated semiconductor structures were first proposed by Esaki and Tsu(1) in order to fabricate electronic oscillators. The material system that they proposed was alternate layers of GaAs and Alx Ga1−x As in order to achieve a modulation in the band edges and to create confined states in the GaAs layers, which in this case acted as...
Article
At temperatures below around 70 K electron-LO phonon scattering freezes out and electron-electron scattering becomes the most important scattering process and limits the coherence length of electrons. Thus electron-electron scattering limits the size and performance of quantum interference devices. We calculate the electron-electron scattering leng...
Article
Hot electron luminescence spectroscopy of GaAs shows polarization dependent lineshape variations of 0.5 approximately 1.0 meV. It is shown how a lineshape model which includes a k.p calculation of the band structure, optical transition matrix elements in the dipole model, and lifetime broadening, is able to explain these polarization effects. For l...
Article
At helium temperatures electron–electron scattering determines the phase breaking and therefore limits the size of quantum interference devices. The electron–electron scattering times and scattering lengths are calculated numerically for ideal single mode quantum wires. The striking result of the present work is that there is no saturation of the e...
Article
Optical properties of GaAs quantum-wire crystals are investigated by means of time-resolved photoluminescence measurements. Recombination dynamics of carriers in the quantum-wire crystals are characterized on the basis of a rate equation which includes surface recombination and effect of depletion layer. Surface treatment with sulphur solution decr...
Article
In conjunction with Raman scattering measurements, we have performed calculations of the electronic structure of nominally δ-doped GaAs:Si in which tthe dopand layer has been positioned close to the surface, with a 200° Å spread towards the surface. The band-bending due to the Fermi level pinning at the surface gives rise to a strong asymmetric sha...
Article
We present and analyse electronic Raman scattering results on a single modulation-doped GaAs quantum well with an high electron density and a thin spacer layer. Coupling with a parallel sheet of electrons is demonstrated.
Article
The electron‐electron scattering time τ ee for a hot electron with excess energy Δ above the Fermi surface of a two‐dimensional (2D) electron gas is calculated as a function of temperature, carrier density, and excess energy Δ for a typical heterostructure. τ ee increases with decreasing temperature and saturates for temperatures below kT≪Δ. The el...
Article
We show that electronic Raman scattering measurements of the intrasubband plasmon dispersion in a GaAs/A1GaAs heterojunction is a viable contactless optical method for the determination of sheet carrier density of the two-dimensional electron gas. We demonstrate non-persistent optical control of the carrier density by a dynamic charge transfer effe...
Article
STRACT We use Raman scattering to investigate direct gap Si/Ge superlattices for which the Si layers are in the form of biatomic sheets. We find a characteristic signal arising from the presence of the biatomic Si sheets. A range of samples have been investigated and 3-dimensional lattice dynamical calculations have been performed which pinpoint th...
Article
We find that the incorporation of a biatomic sheet of either Si or Ge into a Si/Ge short-period superlattice gives rise to a distinctive Raman spectrum in the wave-number range 370-410 cm-1. We prove that this signal is due to the interfaces of the superlattice and originates from phonon modes within the superlattice, which should not normally be o...
Article
Using Raman spectroscopy we have investigated the spacing of the electron subbands in nominally δ‐doped GaAs structures which show a considerable spread of the silicon dopant atoms along the growth direction. For optical excitation in resonance with the E 0 +Δ 0 band gap, spin‐density intersubband excitations are observed. For excitation in resonan...
Chapter
We show that electronic Raman scattering measurements of the plasmon dispersion, in combination with calculations of the RPA dielectric response and self-consistent electronic subband calculations, can be used to determine the subband structure and populations of modulation-doped GaAs/AlxGa1-xAs heterostructures. Thus we present a contactless optic...
Chapter
Electronic Raman scattering is a very powerful technique for the contactless optical characterization of quantum wells and heterojunctions and has much promise for the spatially resolved characterization of quantum wire structures. We show that electronic Raman scattering measurements of the plasmon dispersion is a contactless optical alternative t...
Article
A distinctive Raman spectrum associated with biatomic sheets of silicon in Si/Ge superlattices has been found in the energy range 370–410 cm<sup>-1</sup>. This double‐peaked structure was obtained over an order of magnitude of germanium layer thickness, but was not found in the alloy control layers or structures with thicker Si layers. It is propos...
Article
We report electronic Raman scattering measurements of the plasmon mode in a single GaAs/AlGaAs heterojunction, with a δ layer of acceptors in the GaAs buffer a well‐defined distance from the interface. Under illumination above the band gap of the AlGaAs barrier, a dynamic charge‐transfer effect occurs in which the quasi‐two‐dimensional electron con...
Article
We present the results of full three-dimensional calculations of phonon frequencies in silicon-germanium strained-layer superlattices (SLS’s) and compare with experimental data. We use a modified version of the six-parameter valence-force-potential model, incorporating the strained nature of the layers. We confirm that the dispersion relations for...
Article
We deduce the Γ→L intervalley and polar optic phonon scattering times of hot electrons in bulk GaAs from cw hot (e,A<sup>0</sup>) luminescence spectra at low excitation densities and their dependence on electron kinetic energy. We obtain the lifetime broadening due to these two processes from comparison with line shape calculations using a 16×16 k∙...
Article
We deduce the F-L intervalley and poiar optic phonon scattering times of hot electrons in bulk GaAs from cw hot (e, A°) luminescence spectra as a function of electron kinetic energy at low excitation densities. We obtain the lifetime broadening due to these two processes from comparison with lineshape calculations using a 16x16 k.p Hamiltonian, a f...
Article
We show that electronic Raman scattering measurements of the plasmon dispersion in combination with calculations of the random phase approximation dielectric response and self‐consistent electronic subband calculations can determine the subband structure and populations of modulation‐doped GaAs/Al x Ga 1-x As multiple quantum wells with multiple su...
Article
We present and analyse electronic Raman scattering results on a single two-dimensional electron gas confined in a single quantum well, measured as a function of the scattering geometry and in the presence of additional illumination.
Article
We show that cw luminescence spectroscopy of the cascade of electrons in the conduction band of III-V compound semiconductors relaxing by LO-phonon emission yields information on the band structure, on electron-phonon, electron-electron, and intervalley scattering rates, and on impurity levels at higher-conduction-band minima in III-V compound semi...
Article
We present a fully three-dimensional calculation for the frequencies and the Raman intensities of confined phonons in SiGe [001] strained layer superlattices, on a silicon substrate. We take account of the strain in the calculation. The valence force method is used to calculate the phonon frequencies and the related bond polarizability method to c...
Article
Both the LO-phonon scattering time and the Γ→L intervalley scattering time for electrons in the conduction band of GaAs are of fundamental importance, and they are needed for the modelling of devices. We measure the steady state distribution of hot electrons in lightly p-doped bulk GaAs under carrier densities of 1013–1014cm−3, which is orders of m...
Article
Using electronic Raman scattering and calculations of the full random-phase-approximation inverse dielectric function, we show that in a modulation-doped GaAs/AlxGa1-xAs multiple-quantum-well structure with N quantum wells and M occupied subbands per well, the intrawell interactions split the plasmon dispersion into M groups of modes. The interwell...
Article
In this communication, we present the results of full three dimensional calculations of phonon frequencies in silicon-germanium strained-layer superlattices. We used a modified version of the six-parameter valence force potencial model (VFPM), incorporating the strained nature of the layers. We found that the VFPM reproduces the predicted strain-in...
Article
We report Raman measurements of the LO phonon modes confined in GaAs/AlAs quantum wells grown by refined MBE with and without growth interruption and by migration enhanced epitaxy (MEE). The energies of the confined LO phonon modes lie close to the values expected from the bulk GaAs phonon dispersion. We show that the higher order confined phonon m...
Chapter
We determine the electronic structure of p-type modulation doped quantum wells by resonant Raman scattering and using self consistent envelope function calculations. We demonstrate that closely spaced electronic energy levels in wide quantum wells can be determined with high precision from resonant Raman measurements. We determine the conduction ba...
Chapter
We study the in-plane motion of electrons in modulation doped GaAs/AlGaAs multiple quantum wells by resonant Raman scattering. Electrons from donors incorporated in the barriers of these structures drop into the GaAs wells, forming a multilayered 2D electron gas with very high mobility. The long range interlayer Coulomb interaction couples the in-p...