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