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Radiative efficiency of light-emitting materials
Tim GfroererDavidson College, Davidson, NC
- Funded by Research Corporation and the Petroleum Research Fund
A talk given at the SPIE Regional Meeting onOptoelectronics, Photonics, and Imaging (2000)
OutlineMotivationExperimental techniqueMaterial system: InGaAs
Conclusion
Motivation
laser diodes
light-emitting diodes
light is good!
heat is bad!
sam p le d e te c to r
lig h t inlig h t o u t
e sc ap e co n e
ra d ia tiv eev e n t
sample detectorlight in light out
reabsorptionescape cone
radiativerecombinationevent scattering
refraction
Motivation(continued)
collectionefficiency = ?
sample detectorlight in light out
escape coneradiativerecombinationevent
internalreflection
scattering
refractionreabsorption
Measuring the efficiency
th e rm o m e te r
p h o to d e te c to rlight in
heat
signal light out
light in = heat + light out
T heat
efficiency = light in / light out
la se r
co n s ta n ttem p e ra tu rere se rv o ir
sam p le
th e rm o m e te r
v ac u u m
p h o to -d e te c to r
ex c h an g eg as
Experimental set-up
light in
light out
- heat
100 120 140 16040
50
60
70
80
90
rela
tive
ligh
t sig
nal
relative heating
Efficiency calibration
increasingexcitation
excitation light + heat
Calibrated efficiency
30
40
50
60
70
1015 101710161014
abso
lute
eff
icie
ncy
(%)
excitation rate (s-1)
defects
light
Auger
Nonradiative mechanisms
e le c tro n s
h o le
p h o n o n s
defects:
Auger:e le c tro n
h o le
e le c tro n
h o le
p h o n o n s
5.6 5.8 6.0
0.5
1.0
1.5
Ban
dgap
ene
rgy
(eV
)
Atom spacing (Angstroms)
GaInAs bandgap
GaAs
InAs
InP substrate
Ga0.5 In0.5 As
Lattice mismatch
misfit dislocationsand strain
e le c tro n s
h o le
Auger activation
Conductionband
Valenceband
energy
momentum
Easmaller
Ea
smallerbandgap:
ConclusionsNew radiative efficiency measurement technique
Material system: InGaAsRecombination and Lattice mismatch