How was LED technology born and developed over time? Let's discover it through a historical and technical analysis.
The development of LEDs began with infrared and red devices made with Arsenide of Gallium (GaAs). Advances in materials science have made it possible over the years the production of devices with wavelengths shorter and shorter, and consequently with different colors. The first solid diode that emitted light was made in 1907 by H. J. Round, but it was made no use
of this discovery for several decades, until the invention of the first LED
by Nick Holonyak Jr in 1962, eventually commercialized at the end of the 1960s. The first GaAsP (Gallium Arsenide Phosphide) LEDs combine three primary elements (Gallium, Arsenic and Phosphorus) to produce red light at 655nm. Since the light intensity obtained was limited, they were only used in few applications, essentially as indicators. In the following years they were
developed only GaAsP and GaP (Gallium Phosphide) LED red light. As LED technology progressed, in the 1970s, it became possible to recreate additional colors and wavelengths: the most common materials were green and red by GaP, orange by GaAsP, red and yellow by GaAsP. With the evolution of materials for LED technology, it increased the luminous flux and the LEDs became
bright enough to be used first fornot only electronic applications, but also typical applications of everyday life (computers and digital clocks), and finally for lighting, a field that is still being studied and researched today. In the ‘80s it was developed a new material, the GaAlAs (Arsenide of Aluminium of Gallium).
This development was followed by a rapid growth in the use of LEDs: the
GaAlAs technology provides superior performance compared to LEDs
previously available. The required voltage is lower, and this results in
in a substantial energy saving. In this period, the LEDs were
also inserted into barcode scanners, fiber-optic transmission data systems, and in medical equipment. Improvements in crystal materials and the design of the optics allowed the development of yellow, green and orange LEDs, but it was obtained only a slight improvement in brightness and efficiency, because the basic structure of the material had remained substantially unchanged. As soon as the laser diodes with visible spectrum emission began to be
marketed, in the late 1980s, LED designers experimented with
similar techniques to produce high-brightness and reliable LEDs. This led to
the development of InGaAlP (Indio Gallium Aluminium Phosphide) LEDs, with emission of
visible light: through the optimization of the energy jump in the material InGaAlP
you can have different colors of the light emitted so it could be produced
Green, yellow, orange and red LEDs using the same technology,
also relying on the fact that the degradation of the new material is
In 1993, at Nichia Chemical Industries in Japan, Shuji Nakamura
introduced the blue LED, the most difficult one to produce because of its high photonics energy and the low sensitivity of the human eye to low wavelengths.
The technology used to produce these LEDs is very different and less advanced
compared to the one used for common LEDs, but the importance of this invention has been
remarkable: blue is a primary color, and by combining through a special software the three
Fundamental monochromatic lights (red, green and blue) you can get white light.
This is how the first multichip LEDs (i.e. with three chips of the three basic colors) are created to obtain white light.
Blue LEDs available today are GaN (Gallium Nitrite) and SiC (Silicon Carbide), and
their availability in industrial quantities on the market has resulted in a whole
generation of new applications that include telecommunications products,
applications to means of transport, traffic control systems, and screens for
communications and TV.
Currently, new light-emitting diodes are being developed and realized with a
technology involving a cathode-ray substrate prepared with a different material
from the semiconductor in which the actual junction is made; the particular resulting structure is aimed at obtaining emissions on particular wavelengths
or within a certain spectrum not achievable by common LEDs, everything is made containing the costs. Techniques with a substrate other than the one of the junction are currently
used to obtain LEDs that emit blue light, but also white or UV.