7.2 Internal Quantum Efficiency Improvement Technology
119
field is formed in the active region, which causes spatial separation of the InGaN
conduction band and the valence band electron hole wave function, resulting in a
decrease in the probability of radiation recombination. This is the Quantum-Confined
Stark Effect (QCSE). This is shown in Fig. 7.6. On left side the energy band diagram
without electric field is shown as a flat band. The wave functions of electron and
hole are overlap completely. When an external electric field is applied, and shown
on the right side of Fig. 7.6, the energy band of conduction band and the valence
band will tilt. The wave functions of electrons in the conduction band and holes in
the valence band will be spatially separated, resulting in greatly reduced probability
of wave function overlap. The probability of radiation compounding decreases.
The polarization electric field caused by lattice mismatch in the active region of
InGaN is the main cause of the QCSE effect and the reduction of luminous efficiency.
For nitride compounds, the spontaneous polarization electric field can be calculated
by the following expressions [9]:
P
SP
Al x Ga 1 - x N = −0.090x − 0.034(1 − x) + 0.019x(1 − x),
P
SP
In x Ga 1 - x N = −0.042x − 0.034(1 − x) + 0.038x(1 − x),
P
SP
Al x In 1 - x N = −0.090x − 0.042(1 − x) + 0.071x(1 − x),
(7.1)
Fig. 7.6 QCSE in InGaN
quantum wells
119
field is formed in the active region, which causes spatial separation of the InGaN
conduction band and the valence band electron hole wave function, resulting in a
decrease in the probability of radiation recombination. This is the Quantum-Confined
Stark Effect (QCSE). This is shown in Fig. 7.6. On left side the energy band diagram
without electric field is shown as a flat band. The wave functions of electron and
hole are overlap completely. When an external electric field is applied, and shown
on the right side of Fig. 7.6, the energy band of conduction band and the valence
band will tilt. The wave functions of electrons in the conduction band and holes in
the valence band will be spatially separated, resulting in greatly reduced probability
of wave function overlap. The probability of radiation compounding decreases.
The polarization electric field caused by lattice mismatch in the active region of
InGaN is the main cause of the QCSE effect and the reduction of luminous efficiency.
For nitride compounds, the spontaneous polarization electric field can be calculated
by the following expressions [9]:
P
SP
Al x Ga 1 - x N = −0.090x − 0.034(1 − x) + 0.019x(1 − x),
P
SP
In x Ga 1 - x N = −0.042x − 0.034(1 − x) + 0.038x(1 − x),
P
SP
Al x In 1 - x N = −0.090x − 0.042(1 − x) + 0.071x(1 − x),
(7.1)
Fig. 7.6 QCSE in InGaN
quantum wells