Milestone-Proposal:Realization of Blue Light Emitting Diode, 1989-1993
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Docket #:2024-32
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To the proposer’s knowledge, is this achievement subject to litigation? No
Is the achievement you are proposing more than 25 years old? Yes
Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes
Did the achievement provide a meaningful benefit for humanity? Yes
Was it of at least regional importance? Yes
Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes
Has the IEEE Section(s) in which the plaque(s) will be located agreed to arrange the dedication ceremony? Yes
Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes
Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes
Year or range of years in which the achievement occurred:
1989-1993
Title of the proposed milestone:
Realization of Blue Light Emitting Diode, 1989-1993
Plaque citation summarizing the achievement and its significance; if personal name(s) are included, such name(s) must follow the achievement itself in the citation wording: Text absolutely limited by plaque dimensions to 70 words; 60 is preferable for aesthetic reasons.
In 1989, Isamu Akasaki and Hiroshi Amano achieved the crystal growth and pn junction of gallium nitride, which is suitable for blue light-emitting diodes (LEDs). In 1993, Shuji Nakamura realized a high-brightness blue LED. Blue LEDs are used in many fields such as lighting and have significantly contributed to the expansion of various industries. For this achievement, the three were awarded the Nobel Prize in Physics in 2014.
200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.
Red and green light emitting diodes, which emit the long wavelengths of visible light were invented earlier. However, proper semiconductor material for blue light emitting diodes had not been found until the innovations in this milestone arrived.
The basic structure of blue LEDs is a pn junction, and the principle of light emission through the recombination of electrons in conduction band and holes in valence band is the same as for other LEDs. The realization of blue LEDs involved many challenges, including selecting a material with a large band gap width necessary to emit blue light, achieving high-quality crystal growth, realizing pn junctions, and issues involved in mass production.
In 1989, Isamu Akasaki and Hiroshi Amano achieved the crystal growth and pn junction of gallium nitride (GaN), which is suitable for blue light-emitting diodes (LEDs). In 1993, Shuji Nakamura realized a high-brightness blue LED, that led to mass production.
Blue LEDs are used in many fields such as lighting and have significantly contributed to the expansion of various industries. For this achievement, the three were awarded the Nobel Prize in Physics in 2014.
The realization of blue LEDs has enabled energy savings, long life, and high-quality lighting, significantly impacting the advancement of medical technology and expanded the whole industry sector. This innovation distinguishes itself from other blue light-emitting technologies, such as electroluminescence and blue lasers.
IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.
IEEE Consumer Technology Society, IEEE Electron Devices Society
In what IEEE section(s) does it reside?
IEEE Nagoya Section
IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:
IEEE Organizational Unit(s) paying for milestone plaque(s):
Unit: IEEE Nagoya Section
Senior Officer Name: Jun Sato
IEEE Organizational Unit(s) arranging the dedication ceremony:
Unit: IEEE Nagoya section
Senior Officer Name: Jun Sato
IEEE section(s) monitoring the plaque(s):
IEEE Section: IEEE Nagoya Section
IEEE Section Chair name: Jun Sato
Milestone proposer(s):
Proposer name: Chiaki Ishikawa
Proposer email: Proposer's email masked to public
Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.
Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):
C-TEFs, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
GPS Coordinates: 35.1510357,136.9709546,17
Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.
Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. It is a university research center. It is a comprehensive research facility of the gallium arsenide (GaN), the core of the original blue LED. The facility is the only GaN research center in the world that vertically integrates crystal growth, characterization, device design and processing, and circuitry and systems under-one-roof, and is a new facility that will accelerate research and development.
Are the original buildings extant?
No. But the C-TEFs building near the original building is located on the same Nagoya University campus.
Details of the plaque mounting:
The plaque will be displayed in the entrance hall of C-TEFs building, Nagoya University.
How is the site protected/secured, and in what ways is it accessible to the public?
The plaque will be fixed on the wall of entrance hall in C-TEFs building, Nagoya University, which is accessible to the public with permission.
Who is the present owner of the site(s)?
Hiroshi Amano
What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include detailed support at the end of this section preceded by "Justification for Inclusion of Name(s)". (see section 6 of Milestone Guidelines)
Justification of name in citation
In 1989, Isamu Akasaki and Hiroshi Amano achieved crystal growth and pn junction of gallium nitride (GaN), suitable for blue light emission. In 1993, Shuji Nakamura realized a high-brightness blue light emitting diode (LED). Blue LEDs are used in many fields, such as lighting, and have significantly contributed to the expansion of various industries. For this achievement, the three were awarded the Nobel Prize in Physics in 2014. The reason for the award was "the invention of a blue light emitting diode that enabled a high-brightness, power-saving white light source." This shows that their research has had a tremendous impact on the scientific community and society as a whole.
Advances in science and technology: The invention of blue LEDs has led to breakthroughs not only in lighting technology but also in many fields such as medicine, communications, and electronics. Given such a wide range of influences, inscribing their names on plaques is necessary to convey their historical significance to future generations.
For students and young researchers, their names become a symbol of passion and dedication to the development of science and technology. It is hoped that leaving their names on the plaque will inspire the next generation and encourage new inventions and discoveries.
For these reasons, including the names of Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura on the plaque is of great significance in honoring their technical and social contributions.
Historical Significance
Background
Among visible light wavelengths (λ = 380 nm - 760 nm), diodes existed that emitted long-wavelength red (λ = 630 nm, typical) and green light (λ = 530-540 nm, typical). However, there were no diodes that emitted blue light. As a result, it was not possible to create white light through additive color mixing (red, green, blue) for lighting and display purposes.
Realization of Blue Light Emitting Diode (LED)
Light Emitting Diode (LED)
The basic structure of a light emitting diode (LED) is a pn junction, where a p-type semiconductor (which has many holes) and an n-type semiconductor (which has many electrons) are joined. When a forward voltage is applied to this element, the holes and electrons move toward the pn junction and recombine, causing the electrons to move from a high-energy state in the conduction band to a low-energy state in the valence band. The energy difference (bandgap) between these states is released as light.
Condition for Blue Light Emission
The working principle of blue light emitting diodes (LEDs) is the same as that of general diodes. They emit light when electrons recombine with holes in the pn junction. The bandgap in which the electrons fall into the valence band determines the color emitted.
The bandgap (Bg) [eV] and the wavelength (λ) in micrometer [μm] of
the emitted color are approximately related by the following forumla.:
λ＝1.24/Bg
To emit blue light (λ = 0.46-0.47 μm, typical), a semiconductor with a bandgap of about 2.6 eV is required.
The challenges in realizing a blue LED
The basic structure of a blue light emitting diode (LED) is the same as that of conventional diodes, featuring a pn junction. The principle of light emission, where electrons in a conductor emit light by recombining with holes, is also the same as that of ordinary diodes. Therefore, the challenges in realizing a blue LED included:
(a) Creating a crystal with a wide bandgap that can emit blue light;
(b) Making high-quality pn junctions;
(c) Producing a high-brightness light emitting diode.
The Nobel Prize in Physics
In 1989, Isamu Akasaki and Hiroshi Amano achieved the crystal growth and pn junction of gallium nitride (GaN), which is suitable for blue light emission. In 1993, Shuji Nakamura realized a high-brightness blue LED. For this achievement, Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura were awarded the Nobel Prize in Physics in 2014 [1]. The reason for the award was "the invention of a blue light emitting diode that enabled a high-brightness, power-saving white light source."
Social Impact of the Realization of Blue Light Emitting Diodes
The realization of blue light emitting diodes (LEDs) has had numerous social impacts. Here are some examples:
(a) Energy savings: Blue LEDs are very energy efficient compared to traditional incandescent and fluorescent bulbs, resulting in a significant reduction in electricity consumption. This has lessened the environmental burden and promoted sustainable energy use.
(b) Long service life: Blue LEDs have a very long lifespan and need to be replaced infrequently, which reduces maintenance costs. This has alleviated the economic burden and contributed to waste reduction.
(c) High-quality lighting: Blue LEDs have a high color temperature and provide brightness close to natural light. This has improved both the environment and the quality of work, as well as enhanced visual comfort.
(d) Advances in medical technology: Blue LEDs are also being utilized in the medical field. For example, they are used in phototherapy and dental procedures. This has increased the effectiveness of treatments and improved patients' quality of life.
The scale of the blue LED industry is expanding year by year, and further technological innovations and market expansion are expected in the future. Thus, blue LEDs have become an essential technology in many industries.
What obstacles (technical, political, geographic) needed to be overcome?
Obstacles to overcome
Materials for blue light emission
To emit blue light (λ= 450-470 nm, typical), a semiconductor with a bandgap of about 2.6 eV is required. Silicon (Si) with a bandgap of 1.2 eV and gallium arsenide (GaAs) with a bandgap of 1.4 eV, which were commonly used at the time, did not meet these conditions due to their narrow bandgaps. Therefore, gallium nitride (GaN), zinc selenide (ZnSe), and silicon carbide (SiC) with wider bandgaps were considered as candidates for blue light emitting semiconductors. However, SiC had indirect bandgap and low light emission efficiency. ZnSe was advantageous because it had the same atomic spacing as GaAs, leading many researchers to attempt to create crystals with ZnSe. However, ZnSe proved unsuitable for practical use due to its brittleness. GaN did not have a suitable substrate, and few researchers focused on it. Nonetheless, Akasaki and Amano chose GaN as their material [2], and their pioneering work led to significant advancements in blue LED technology.
Base material for GaN
Akasaki and Amano chose sapphire (aluminum oxide, α-Al2O3) as the substrate for GaN crystal growth due to its affordability, resistance to high temperatures and ammonia, and overall durability. Initially, they encountered difficulties in growing GaN on a sapphire substrate. They first explored the halogen vapor phase epitaxy (HVPE) method, making numerous improvements to the reaction tube and substrate. However, controlling the temperature proved challenging with this method. Subsequently, Akasaki switched to the metal-organic vapor phase epitaxy (MOVPE) method, which successfully enabled the growth of GaN crystals [3].
Crystal growth of GaN
Sapphire and GaN have different crystal structures, with a 16% difference in atomic spacing. Consequently, clean GaN crystal growth on the sapphire substrate was initially not possible. To address this, Amano devised a low-temperature buffer layer consisting of aluminum nitride (AlN) impurities sandwiched between the sapphire substrate and GaN. As a result, high-quality GaN crystal growth was achieved on a sapphire substrate [4],[5].
Preparation of p-type GaN crystals
In principle, the GaN base is n-type. To create a pn junction diode, it is necessary to grow p-type GaN on this n-type GaN base. It was common practice to use zinc (Zn) as the dopant to create p-type GaN; however, this approach was unsuccessful. Therefore, Amano explored the use of magnesium (Mg), which had not been previously tried as a GaN dopant. They discovered a phenomenon called low-energy electron beam irradiation (LEEBI), where cathodoluminescence becomes stronger when electron beams are irradiated on Mg-doped GaN. Through this method, he successfully achieved the growth of p-type GaN on top of the n-type GaN substrate [6].
Semiconductors with a bandgap that emits blue light
The bandgap of GaN is 3.4 eV, which emits ultraviolet light, having a shorter wavelength (λ~ 0.36μm) than blue visible light (λ > 0.38μm). In other words, Akaike and Amano developed an LED that emits a faint blue glow in visible light region, as shown in Figure 1 [13].
Figure 1 Blue LED by Akasaki and Amano (from the cover of [13]).
To achieve the emission of
blue light, the following two approaches were tried by Akaike and Amano.
(i) Mixing impurities with a shorter bandgap into the light emitting layer.
(ii) Designing an energy level where electrons fall from the donor
level to the acceptor level, rather than from the conduction band to
the valence band.
Indium nitride (InN), which has a bandgap of 0.7 eV, was mixed with the hope of
reducing the overall bandgap to about 2.6 eV. However, it was
difficult to synthesize inidium garium nitride (InGaN) crystals using the high-pressure methods
known at the time.
This issue was resolved by developing a technique to utilize a large amount of ammonia gas during growth [7].
Mixed crystal growth of InGaN
It was challenging to create a large mixed crystal of InGaN with a bandgap suitable for blue light emission due to poor gas flow within the reaction tube. Nakamura addressed this issue by devising the "Two Flow MOCVD Method" to regulate gas flow[8],[9].
Double heterojunction in which Ingang is sandwiched between GaN
In a simple pn junction composed of two layers, sufficient blue luminescence brightness could not be obtained with just a p-type GaN layer. This is because GaN tends to emit purple and ultraviolet light due to its bandgap size.
Nakamura grew a GaN layer on a sapphire substrate without creating an AlN layer, successfully forming a large indium gallium nitride (InGaN) mixed crystal. InGaN had a bandgap suitable for emitting blue visible light.
In 1993, Nakamura devised a double heterostructure in which the light emitting layer of InGaN is sandwiched between two layers of GaN, one p-type and one n-type. In addition, he devised a quantum well structure in which p-type and n-type GaN were modified into a mixed crystal of aluminum gallium` nitride (AlGaN) with an even larger band gap. This development led to a blue light emitting diode that emits high-brightness blue light in the InGaN layer [10],[11].
What features set this work apart from similar achievements?
Features set this work apart from similar achievements
Mechanism to emit blue light
In addition to blue light emitting diodes (LEDs), there are several other methods to emit blue light. For example, neon signs use blue neon gas, fluorescent lamps and CRTs emit blue light through X-rays and cathode rays using blue phosphors. However, these methods have disadvantages, such as requiring large amounts of power and difficulty in miniaturization.
Furthermore, after the development of blue LEDs, blue lasers were created as an extension of the technology, capable of emitting blue light at specific wavelengths. Additionally, electroluminescence is another phenomenon where certain chemicals emit blue light when an electric current passes through them.
Realization methods of blue light emitting diode
In 1974, there was a report of a MIS-type blue light emitting diode that combined metal and semiconductor, differing from PN junction diodes. However, this method resulted in poor luminous efficiency and insufficient brightness [12].
Why was the achievement successful and impactful?
Why was the achievement successful and impactful?
Here's why it was so successful and impactful:
(a) Technological breakthroughs: The breakthroughs made by Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura shattered the limits of conventional technology. The realization of high-quality crystal growth and pn junctions using gallium nitride (GaN) and the development of high-brightness blue light emitting diodes (LEDs) were impossible with previous technologies. This achievement revolutionized lighting technology by enabling the creation of blue LEDs.
(b) Extensive application and social impact: The realization of blue
LEDs has brought numerous benefits, such as increased energy
efficiency, energy savings, long life, and high-quality
lighting. These advancements have reduced environmental impact,
promoted sustainable energy use, and significantly contributed to the
expansion of various industries. Additionally, blue LEDs have been
applied in diverse fields, including medical technology, communication
technology, and electronics, greatly impacting society as a whole.
(c) Recognition through the Nobel Prize: In 2014, the three scientists
who contributed to the realization of blue LEDs were awarded the Nobel
Prize in Physics, recognizing their technical achievements and social
impact on an international scale. The award cited "the invention of
the blue light emitting diode, which has enabled bright and
energy-saving white light sources," highlighting the profound impact
their research has had on both the scientific community and society.
For these reasons, the realization of blue LEDs stands as a technological triumph and an achievement with significant social impact.
Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.
Bibliography
[1] https://www.nobelprize.org/prizes/physics/2014/summary/
[Remarks] The Nobel Prize in Physics 2014 was awarded jointly to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura "for the invention of efficient blue light emitting diodes which has enabled bright and energy-saving white light sources".
[2] H. Amano, H. Akasaki, “Characterization of Zn-doped GaN grown by MOVPE,” Applied Physics Letters, vol. 48, no. 5, 1986.
[3] I. Akasaki, H. Amano, K. Itoh, “AlN buffer layer grown at low temperature for recrystallized GaN on sapphire substrate,” Japanese Journal of Applied Physics, vol. 27, no. L202, 1988.
[4] I. Akasaki, H. Amano, K. Itoh, “AlN buffer layer grown at low temperature for recrystallized GaN on sapphire substrate,” Japanese Journal of Applied Physics, vol. 27, no. L202, 1988.
[5] H. Amano, K. Hiramatsu, N. Sawaki, I. Akasaki, “AlN buffer layer grown at low temperature for growth of GaN on sapphire substrate,” Japanese Journal of Applied Physics, vol. 27, no. L1384, 1988.
[6] H. Amano, M. Kito, K. Hiramatsu, I. Akasaki, “P-type conduction in Mg-doped GaN treated with low-energy electron beam irradiation (LEEBI),” Japanese Journal of Applied Physics, vol. 28, no. L2112, 1989.
[7] H. Amano, H. Akasaki, “Growth and device application of GaN-based materials,” Materials Research Society Symposium Proceedings, vol. 281, 1993.
[8] S. Nakamura: “High-brightness InGaN blue, green and yellow light-emitting diodes”, Japanese Journal of Applied Physics, Vol. 34, Part 1, No. 7A, pp. L797–L799, 1995.
[9] S. Nakamura: “Two-flow MOCVD of GaN growth using GaCl”, Journal of Crystal Growth, Vol. 170, pp. 411–414, 1997
[10] S. Nakamura, M. Senoh, T. Mukai, “P-GaN/N-InGaN/N-GaN double-heterostructure blue-light-emitting diodes,” Japanese Journal of Applied Physics, vol. 32, no. L8-L11, 1993.
[11] S. Nakamura, T. Mukai, M. Senoh, “High-brightness InGaN/AlGaN double-heterostructure blue-green-light-emitting diodes,” Applied Physics Letters, vol. 64, no. 13, pp. 1687-1689, 1994.
[12] J. P. Pankove and M. A. Lampert: ” Model for Electroluminescence in GaN”, Physical Review Letters, pp. 361-364, Vol. 3, No. 6, 1974
[13] Isamu Akasaki; “Fascinated by the blue light -The story of the development of blue LEDs-“, NikkeiBook, ISBN978-4-532-16851-3, 2013.
[Remarks] Only the photo on the inside cover of the book is referenced. The book is authored by Isamu Akasaki, one of the inventors of blue LEDs. This photo is reprinted from the inside cover of the book. The title of the book is written in Japanese on the first line on the far right, and the author's name is written on the second line.
Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to ieee-history@ieee.org. Please see the Milestone Program Guidelines for more information.
Please email a jpeg or PDF a letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property, and a letter (or forwarded email) from the appropriate Section Chair supporting the Milestone application to ieee-history@ieee.org with the subject line "Attention: Milestone Administrator." Note that there are multiple texts of the letter depending on whether an IEEE organizational unit other than the section will be paying for the plaque(s).
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