Chapter 5
InGaN/GaN Multiple Quantum Wells
Materials as Well as Blue and Green
LEDs
InGaN/GaN quantum wells are commonly used in III-nitride based blue or green
LED chips. Back in the earlier days, it was difficult for GaN materials to be doped
for the formation of high crystal quality p-type GaN. The first GaN-based LED introduced in 1971 could only adopt MIS (metal-insulator-semiconductor) structure. In
1986, Hiroshi Amano and Akasaki et al. [1] demonstrated GaN films with a good
surface structure and high crystal quality by MOCVD through low-temperature AlN
buffer epitaxial layer. In 1989, Amano et al. [2] used low-energy electron irradiation (LEEBI) technology and successfully achieved p-type doping of GaN materials.
These breakthrough technologies accelerated the development of LED. This led to
the rapid progress in terms of output power, quantum efficiency, spectral quality,
etc. However, InGaN/GaN multiple quantum wells LEDs also face many problems.
Currently, InGaN-based LEDs are grown on the c-plane sapphire along the [0001]
polarization direction. The InGaN quantum well is in a compressed elastic deformation, and a piezoelectric polarization field is produced along the growth direction
up to the order of MV/cm. The polarized electric field will aggravate the quantum
confined Stark effect (QCSE) in the InGaN quantum well, which causes the separation of electron and hole wave functions in the quantum well and reduces the
probability of radiation recombination. At the same time, the polarized electric field
will also cause carriers to leak from the well, which reduces the carrier concentration
involved in radiation recombination and aggravates the droop effect. These will be
discussed in subsequent chapters.
In addition, the dislocation density in InGaN/GaN multiple quantum wells grown
on c-plane sapphire is very high. On the other hand, the internal quantum efficiency
of InGaN LEDs is actually not low: the internal quantum efficiency of blue LEDs
exceeds 80% and about 60% for green LEDs. This phenomenon has a lot to do
with the localization of carriers in InGaN/GaN multiple quantum wells. Both the
localization effect and the quantum confined Stark effect affect the spontaneous
emission of InGaN/GaN multiple quantum wells.
© 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_5
75
InGaN/GaN Multiple Quantum Wells
Materials as Well as Blue and Green
LEDs
InGaN/GaN quantum wells are commonly used in III-nitride based blue or green
LED chips. Back in the earlier days, it was difficult for GaN materials to be doped
for the formation of high crystal quality p-type GaN. The first GaN-based LED introduced in 1971 could only adopt MIS (metal-insulator-semiconductor) structure. In
1986, Hiroshi Amano and Akasaki et al. [1] demonstrated GaN films with a good
surface structure and high crystal quality by MOCVD through low-temperature AlN
buffer epitaxial layer. In 1989, Amano et al. [2] used low-energy electron irradiation (LEEBI) technology and successfully achieved p-type doping of GaN materials.
These breakthrough technologies accelerated the development of LED. This led to
the rapid progress in terms of output power, quantum efficiency, spectral quality,
etc. However, InGaN/GaN multiple quantum wells LEDs also face many problems.
Currently, InGaN-based LEDs are grown on the c-plane sapphire along the [0001]
polarization direction. The InGaN quantum well is in a compressed elastic deformation, and a piezoelectric polarization field is produced along the growth direction
up to the order of MV/cm. The polarized electric field will aggravate the quantum
confined Stark effect (QCSE) in the InGaN quantum well, which causes the separation of electron and hole wave functions in the quantum well and reduces the
probability of radiation recombination. At the same time, the polarized electric field
will also cause carriers to leak from the well, which reduces the carrier concentration
involved in radiation recombination and aggravates the droop effect. These will be
discussed in subsequent chapters.
In addition, the dislocation density in InGaN/GaN multiple quantum wells grown
on c-plane sapphire is very high. On the other hand, the internal quantum efficiency
of InGaN LEDs is actually not low: the internal quantum efficiency of blue LEDs
exceeds 80% and about 60% for green LEDs. This phenomenon has a lot to do
with the localization of carriers in InGaN/GaN multiple quantum wells. Both the
localization effect and the quantum confined Stark effect affect the spontaneous
emission of InGaN/GaN multiple quantum wells.
© 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_5
75