A semiconductor scientist who made pioneering contributions to the realization of the "blue LED dream"
Research and Development of LEDs: Brief history
An LED (Light Emitting Diode) is a semiconductor device that emits light in visible to near infrared wavelengths when a forward direct current is applied to the semiconductor�fs p-n junction, causing electron-hole recombination. As a light source with low energy consumption, LEDs are expected to have a wide range of applications where the primary purpose is saving electricity.
Large-scale studies on LEDs began around 1960, and their emission colors were successively added, including red, orange, and green. However, all attempts to develop "blue" LEDs were fraught with difficulty. Semiconductor researchers continued their work, expecting gallium nitride* (GaN) to emit blue light, but they soon became aware that synthesis of p-type GaN was no easy task. Furthermore, a theoretical report was published which asserted that it was impossible to develop GaN-based blue LEDs. By the late 1970s, many scientists around the world withdrew from their researches and developments. However, the three primary colors of light would be available if blue LEDs could be developed, enabling light emission in any color by combining red, blue, green LEDs.
The road to realization of the "blue LED dream"
Meanwhile, believing in the potential of GaN-based diodes, Dr. Isamu Akasaki remained true to his beliefs and quietly but diligently continued his research. No matter how often he failed, he continued with single-minded determination to devote himself to his research, holding on to the strong conviction that he would eventually succeed.
"Once an objective has been set, a true leader should not waver in the pursuit of it." Faithful to his words, Dr. Akasaki decided to go back to where he had started, namely, synthesis of high-quality GaN crystals. Having hit upon the idea of adopting a new synthesis technique called MOVPE* (Metal-Organic Vapor Phase Epitaxy) and a buffer layer constructed at low temperature, in 1985 Dr. Akasaki succeeded in synthesizing high-quality GaN crystal films. After overcoming many obstacles following that success, in 1989 he finally discovered that magnesium doped high quality GaN crystal had p-type conduction by irradiating with electron beams. In the same year, at an academic conference in the United States, Dr. Akasaki published that he had succeeded in creating blue LEDs. In contrast to his former obscurity, the spotlight came to shine upon his twenty years of diligent research.
Potential of blue LED application
Blue LEDs have already been adapted to a broad range of applications, including displays for mobile electronic devices, large display equipment on streets and at train stations, railway and road traffic signals, and vehicle lamps. Now that application of such technology to blue semiconductor lasers has been made possible, the capacity of optical recording media, such as Blu-ray discs, has been dramatically increased, bringing greater convenience to our daily lives. More recently, LEDs have come to be used in general-purpose lighting, demonstrating their superior energy conserving qualities.
Dr. Akasaki's pioneering research has not only led to numerous and diverse applications to electronics equipment, but has also contributed to protecting the global environment.
For more details, see the Achievements.
*Gallium nitride: Chemical formula; GaN, Its band gap at room temperature; 3.4 eV
*MOVPE (Metal-Organic Vapor Phase Epitaxy): A variety of VPE (Vapor Phase Epitaxy) epitaxial growth. Through a thermal decomposition reaction, compunds are grown on a substrate from gaseous materials, such as hydrides and organometallic compounds.
*P-type semiconductor: Uses holes as majority carriers of electric charge
*N-type semiconductor: Uses electrons as majority carriers of electric charge