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Investigation of Efficiency Droop Behaviors of
InGaN/GaN Multiple-Quantum-Well LEDs With
Various Well Thicknesses
Yun-Li Li, Member, Yi-Ru Huang, and Yu-Hung Lai
IEEE
Outline
Introduction
 Experiment
 Results and Discussions
 Conclusions
 References

Introduction
InGaN/GaN MQW LEDs, a well-known
fundamental problem needs to be overcome,
namely the efficiency “droop”.
Experiment
P
P-GaN(120 nm)
p-type AlGaN/GaN EBL(10 nm/2nm)
Mg-doped p-AlGaInN (10nm)
10-period InGaN/GaN MQW
n-GaN(4 μ m)
LT-GaN (20nm)
sapphire substratrs
LED size 350 ×350 μ m2
N
Results and Discussions
Fig. 1. Normalized EQE measurements of the MQW LEDs with varied well thicknesses. A
reduced efficiency droop behavior is demonstrated for the samples with thicker quantum
wells. The inset shows absolute values of the external quantum efficiencies for the samples.
Fig. 3. Simulation results of IQE at different current densities.
Fig. 2. Schematic figure of total current density Jtotal = Jrad + Jnrad +Joverflow .
RAuger
RAuger
Rdis
Rdis
Fig. 4. Ratios of dislocation recombination rates to total carrier recombination rates, Rdis/Rdis +
Rrad + RAuger , and Auger recombination rates to total carrier recombination rates, RAuger/Rdis + Rrad
+ RAuger, versus total current density. The ratios of dislocation recombination rates are higher than
that of Auger recombination rates at low current densities. As current densities increase, ratios of
dislocation recombination rates decrease and ratios of Auger recombination rates increase.
Fig. 5. Ratios of nonradiative current densities to total current densities Jnrad /Jtotal and carrier
overflow current densities to total current densities Joverflow /Jtotal at different current densities.
Jnrad /Jtotal saturates at current higher than 100 A/cm2 . Joverflow /Jtotal increases as total current
densities increase.
TABLE I
VARIATIONS OF IQE, RATIO OF NONRADIATIVE CURRENT DENSITIES TO TOTAL
CURRENT DENSITIES (JNRAD /JTOTAL ) AND RATIO OF CARRIER OVERFLOW CURRENT
DENSITIES TO TOTAL CURRENT DENSITIES (JOVERFLOW /JTOTAL ) IN DIFFERENT
CURRENT DENSITY RANGES
Conclusions
Simulation results strongly suggest that at current densities from 10
to 100 A/cm2 , Auger recombination is the dominant mechanism for
efficiency droop behaviors, while at current densities from 100 to
200 A/cm2 , carrier overflow becomes the dominant mechanism for
efficiency droop behaviors.
On the importance of radiative and Auger losses
in GaN-based quantum wells
J. Hader, J. V. Moloney, B. Pasenow, S. W. Koch, M. Sabathil, N. Linder, and S. Lutgen
APPLIED PHYSICS LETTERS
Outline



Introduction
Experiment Results and Discussions
Conclusions
FIG. 1. Confinement potentials thick and wavefunctions thin lines for a 2 nm wide
In0.37Ga0.63N/GaN well. Black: nominal well. Gray: well with Gaussian alloy composition.
Dashed lines: energies of the states and zeros of the wavefunctions. Left: N=0. Middle:
N=1014 cm−2. Right: N=0 and internal fields turned off.
325 K
FIG. 2. Carrier lifetime due to radiative recombination for an In0.37Ga0.63N/GaN well at 300 K.
Black/gray: nominal/Gaussian well. Solid/dashed/dotted: for full/half/zero strength of the internal
fields. Thin lines: fields of full strength and 325 K.
Rdis
RAuger
FIG. 3. Loss current for the Gaussian well. Solid: Jrad+JAug; dashed: Jrad; dotted: JAug. Black/dark
gray/light gray: for full/half/zero strength of the internal fields. Thin black: fits according to
Jrad=BN2, B=3.5 10×12 cm2 / s and JAug=CN3, C=3.510×34 cm6 / s.
FIG. 4. Experimental and theoretical threshold current densities for various InGaN-based laser
diodes. Triangles/squares/stars: from Refs.
References
Yun-Li Li, Member, Yi-Ru Huang, and Yu-Hung Lai,”Investigation of Efficiency Droop
Behaviors of InGaN/GaN Multiple-Quantum-Well LEDs With Various Well Thicknesses”.
J. Hader, J. V. Moloney, B. Pasenow, S. W. Koch, M. Sabathil, N. Linder, and S. Lutgen,” On
the importance of radiative and Auger losses in GaN-based quantum wells”.