Chapter 2
Basic Principles of LED
LED is a semiconductor optoelectronic device. In contrast with traditional light
sources, LED has a list of advantages, such as high efficiency, long lifetime, not
easy to break, fast reaction speed and high reliability [1]. These features make the
LED device attractive for luminaire. Its basic structure is a p–n junction. The basic
principle is that electrons and holes in semiconductors recombine and emit photons
under forward bias. In order to fabricate efficient LED, the radiation recombination
probability of electrons and holes in semiconductor must be increased as much as
possible, and the non-radiation recombination probability must be reduced. Due to
the fact that the light-emitting mechanism of LED is completely different from that of
traditional incandescent lamp and other light sources, it also has different optical and
electrical characteristics. In view of the unique optical and electrical characteristics
of LED, we can use monochrome LED to mix color or combine phosphor to achieve
white LED.
This chapter takes p–n junction as the theoretical model, mainly introduces the
basic principle of LED, radiative and non-radiative radiation, the optical and electrical
characteristics of LED, and the realization method of white LED.
2.1 LED Luminescence Principle
2.1.1 History and Principle of Lighting Source
The history of lighting source is as old as human civilization. The lighting history
of human beings has experienced four stages [2]: fire lighting, incandescent lamp
lighting, fluorescent lamp lighting and high intensity gas discharge lamp. Among
them, people use torches, oil lamps and candles as lighting tools for a long time,
but these light sources have low luminous efficiency, lower brightness, incomplete
© Science Press and Springer Nature Singapore Pte Ltd. 2020
J. Li et al., III-Nitrides Light Emitting Diodes: Technology and Applications,
Springer Series in Materials Science 306,
https://doi.org/10.1007/978-981-15-7949-3_2
7
Basic Principles of LED
LED is a semiconductor optoelectronic device. In contrast with traditional light
sources, LED has a list of advantages, such as high efficiency, long lifetime, not
easy to break, fast reaction speed and high reliability [1]. These features make the
LED device attractive for luminaire. Its basic structure is a p–n junction. The basic
principle is that electrons and holes in semiconductors recombine and emit photons
under forward bias. In order to fabricate efficient LED, the radiation recombination
probability of electrons and holes in semiconductor must be increased as much as
possible, and the non-radiation recombination probability must be reduced. Due to
the fact that the light-emitting mechanism of LED is completely different from that of
traditional incandescent lamp and other light sources, it also has different optical and
electrical characteristics. In view of the unique optical and electrical characteristics
of LED, we can use monochrome LED to mix color or combine phosphor to achieve
white LED.
This chapter takes p–n junction as the theoretical model, mainly introduces the
basic principle of LED, radiative and non-radiative radiation, the optical and electrical
characteristics of LED, and the realization method of white LED.
2.1 LED Luminescence Principle
2.1.1 History and Principle of Lighting Source
The history of lighting source is as old as human civilization. The lighting history
of human beings has experienced four stages [2]: fire lighting, incandescent lamp
lighting, fluorescent lamp lighting and high intensity gas discharge lamp. Among
them, people use torches, oil lamps and candles as lighting tools for a long time,
but these light sources have low luminous efficiency, lower brightness, incomplete
© Science Press and Springer Nature Singapore Pte Ltd. 2020
J. Li et al., III-Nitrides Light Emitting Diodes: Technology and Applications,
Springer Series in Materials Science 306,
https://doi.org/10.1007/978-981-15-7949-3_2
7