Chapter 7
III-Nitride LED Quantum Efficiency
Improvement Technology
LED quantum efficiency is one of the important indicators to characterize the performance of LED devices, including internal quantum efficiency and external quantum
efficiency. The internal quantum efficiency refers to the radiation recombination efficiency of electron-hole pairs injected into the active region, which can be improved
by optimizing the epitaxial structure and improving the epitaxial technology. The
external quantum efficiency is the ratio of the number of photons incident into the
space and number of electron-hole pairs in the active region, which is the product of
the internal quantum efficiency and the light extraction efficiency. The improvement
of light extraction efficiency mainly depends on the optimization of chip technology
and packaging technology. In addition, the current injection efficiency is also an
important factor affecting the wall-plug efficiency of the LED, and is related to the
bulk resistance of the LED device, leakage of carriers and electrode contact.
7.1 Three Structures of LED
Up to now, Gallium Nitride (GaN)-based LED chip technology has emerged three
basic device structures including horizontal, flip-chip, and vertical structure. These
three structures have their own advantages and disadvantages in the production and
application process. The following describes the structure of these three devices
separately.
The first type is a lateral structure LED, which can be fabricated by a conventional
planar chip process. Therefore, this is the most easily realized LED chip structure
on an epitaxial wafer with sapphire substrate, and is also a commonly used one.
Figure 7.1 shows the cross-sectional structure of an LED of this structure. In horizontal structure LED chips with non-conductive sapphire substrate, etching process
is needed to expose n-type GaN material. Since p-GaN is very thin, the current
spreading capability is poor. As the p-GaN surface acts as a light-emitting surface,
© 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_7
113
III-Nitride LED Quantum Efficiency
Improvement Technology
LED quantum efficiency is one of the important indicators to characterize the performance of LED devices, including internal quantum efficiency and external quantum
efficiency. The internal quantum efficiency refers to the radiation recombination efficiency of electron-hole pairs injected into the active region, which can be improved
by optimizing the epitaxial structure and improving the epitaxial technology. The
external quantum efficiency is the ratio of the number of photons incident into the
space and number of electron-hole pairs in the active region, which is the product of
the internal quantum efficiency and the light extraction efficiency. The improvement
of light extraction efficiency mainly depends on the optimization of chip technology
and packaging technology. In addition, the current injection efficiency is also an
important factor affecting the wall-plug efficiency of the LED, and is related to the
bulk resistance of the LED device, leakage of carriers and electrode contact.
7.1 Three Structures of LED
Up to now, Gallium Nitride (GaN)-based LED chip technology has emerged three
basic device structures including horizontal, flip-chip, and vertical structure. These
three structures have their own advantages and disadvantages in the production and
application process. The following describes the structure of these three devices
separately.
The first type is a lateral structure LED, which can be fabricated by a conventional
planar chip process. Therefore, this is the most easily realized LED chip structure
on an epitaxial wafer with sapphire substrate, and is also a commonly used one.
Figure 7.1 shows the cross-sectional structure of an LED of this structure. In horizontal structure LED chips with non-conductive sapphire substrate, etching process
is needed to expose n-type GaN material. Since p-GaN is very thin, the current
spreading capability is poor. As the p-GaN surface acts as a light-emitting surface,
© 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_7
113