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7 III-Nitride LED Quantum Efficiency Improvement Technology
Among them, x is the component of the III element. For the epitaxial nitride layer
with a certain degree of lattice mismatch, the piezoelectric polarization electric field
can be expressed as [10]:
P
PZ
X x Y 1 - x N = x P
PZ
XN [ε(x)] + (1 − x)P
PZ
YN [ε(x)]
(7.2)
Among them, the piezoelectric polarization electric field of binary nitride can be
accurately expressed as:
P
PZ
AlN = −1.808ε + 5.624ε
2 for ε < 0,
P
PZ
AlN = −1.808ε − 7.888ε
2 for ε > 0,
P
PZ
GaN = −0.918ε + 9.541ε
2
,
P
PZ
InN = −1.373ε + 7.559ε
2
,
(7.3)
Among them,ε(x) =
a s −a x
a x
. The polarization electric field of the compound
epitaxial layer is the result of the combined action of the piezoelectric polarization
electric field and the spontaneous polarization electric field. Therefore, the polarization electric field of the epitaxial layer can be obtained by the following relationship
[11]:
P c = P SP + P PZ,c (ε)
(7.4)
The polarization electric field in the active region of InGaN is calculated as follows
[11]:
P c = P SP,QW − P SP,QB + P PZ,c (ε)
(7.5)
Based on the above theoretical equation, we can calculate the polarization field
in the InGaN/ GaN active region with different In composition.
The electric field polarization is also influenced by crystal defects. Dislocations
and other defects may generate stress in quantum well region, and impact piezoelectric polarization field. Exploring different approaches to reduce MQWs polarization
electric field and improve the crystal quality has become a major research focus.
In addition, factors affecting the quantum efficiency within the nitride device are
also associated with very low electron capture efficiencies and low hole injection
efficiencies in the multiple quantum well active regions. The activation energy of
Mg-doped p-type GaN is very high. As the hole concentration and mobility are low,
this will lead to a relatively lower hole injection efficiency. In contrast, the mobility
of electron is much higher since the effective mass of the electrons is much smaller
than that of the holes. The electrons, therefore, can leak from the active region into
p-GaN layer and recombine with the holes non-radiatively. This is especially true in
the case of large current injection.
7 III-Nitride LED Quantum Efficiency Improvement Technology
Among them, x is the component of the III element. For the epitaxial nitride layer
with a certain degree of lattice mismatch, the piezoelectric polarization electric field
can be expressed as [10]:
P
PZ
X x Y 1 - x N = x P
PZ
XN [ε(x)] + (1 − x)P
PZ
YN [ε(x)]
(7.2)
Among them, the piezoelectric polarization electric field of binary nitride can be
accurately expressed as:
P
PZ
AlN = −1.808ε + 5.624ε
2 for ε < 0,
P
PZ
AlN = −1.808ε − 7.888ε
2 for ε > 0,
P
PZ
GaN = −0.918ε + 9.541ε
2
,
P
PZ
InN = −1.373ε + 7.559ε
2
,
(7.3)
Among them,ε(x) =
a s −a x
a x
. The polarization electric field of the compound
epitaxial layer is the result of the combined action of the piezoelectric polarization
electric field and the spontaneous polarization electric field. Therefore, the polarization electric field of the epitaxial layer can be obtained by the following relationship
[11]:
P c = P SP + P PZ,c (ε)
(7.4)
The polarization electric field in the active region of InGaN is calculated as follows
[11]:
P c = P SP,QW − P SP,QB + P PZ,c (ε)
(7.5)
Based on the above theoretical equation, we can calculate the polarization field
in the InGaN/ GaN active region with different In composition.
The electric field polarization is also influenced by crystal defects. Dislocations
and other defects may generate stress in quantum well region, and impact piezoelectric polarization field. Exploring different approaches to reduce MQWs polarization
electric field and improve the crystal quality has become a major research focus.
In addition, factors affecting the quantum efficiency within the nitride device are
also associated with very low electron capture efficiencies and low hole injection
efficiencies in the multiple quantum well active regions. The activation energy of
Mg-doped p-type GaN is very high. As the hole concentration and mobility are low,
this will lead to a relatively lower hole injection efficiency. In contrast, the mobility
of electron is much higher since the effective mass of the electrons is much smaller
than that of the holes. The electrons, therefore, can leak from the active region into
p-GaN layer and recombine with the holes non-radiatively. This is especially true in
the case of large current injection.