reliabilityand failureanalysis ofoptoelectronicdevices ve… · reliabilityand failureanalysis...
Post on 12-Jul-2020
4 Views
Preview:
TRANSCRIPT
Reliability and Failure Analysis
of Optoelectronic Devices
Matteo Meneghinia, Massimo Vanzib,
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Matteo Meneghini , Massimo Vanzi ,
Gaudenzio Meneghessoa and Enrico Zanonia
aUniversity of Padova, Department of Information Engineering,
via Gradenigo 6/B, 35131 Padova, Italy
E-mail: matteo.meneghini@dei.unipd.itbUniversity of Cagliari, Italy
Outline
•Operating principles and structure of LEDs and laser diodes
•Degradation of optoelectronic devices
•Degradation of the heterostructure of LEDs and laser diodes
by means of electro-optical techniques
•Analysis of the degradation of the properties of ohmic
contacts of optoelectronic devices
•Degradation processes related to Dark Line Defects
•Degradation of the facets of laser diodes
µE-LAB,
Reliability and failure analysis of optoelectronics devices
•Degradation of the facets of laser diodes
•Conclusions
Recombination processes in semiconductors
µE-LAB,
Reliability and failure analysis of optoelectronics devices
After EF Schubert, Light Emitting Diodes, 2nd
Edition, Cambridge University Press
Surface recombination
µE-LAB,
Reliability and failure analysis of optoelectronics devices
After EF Schubert, Light Emitting Diodes, 2nd
Edition, Cambridge University Press
Light Extraction from LEDs
Light output
LightPlastic dome
Domedsemiconductor
(a) (b) (c)
p
Electrodes Electrodes
pn Junctionn+
n+
(a) Some light suffers total internal reflection and cannot escape. (b) Internal reflections
Substrate
µE-LAB,
Reliability and failure analysis of optoelectronics devices
(a) Some light suffers total internal reflection and cannot escape. (b) Internal reflectionscan be reduced and hence more light can be collected by shaping the semiconductor into adome so that the angles of incidence at the semiconductor-air surface are smaller than thecritical angle. (b) An economic method of allowing more light to escape from the LED isto encapsulate it in a transparent plastic dome.
Structure of a power LED
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Thin-film LEDs
Thin Film technology (ThinGaN) (4 basic steps)
1) High reflectivity p-contact: 2) Wafer bonding
substrate
epitaxy (≈6 µm)
substrate
carriersolder
metal
3) Substrate removal
substrate
Laser Lift Off (for InGaN on sapphire)
4) Surface roughening
µE-LAB,
Reliability and failure analysis of optoelectronics devices
substrate
carrier
basic process patents owned by OSRAM
carrier
increased light extraction
Thin-film LEDs
PowerThinGaN LED structure:• low internal absorption ⇒ thin epi layers
Thinfilm principle:
• prevent absorption in substr. ⇒ highly reflecting mirror
Present actions:
PowerThinGaN LED structure:• low internal absorption ⇒ thin epi layers
GaN
textured surfacecontact
^
Solder layer
QW
• prevent waveguiding ⇒ optimize surface roughness
Mirror layer
1mm
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Carrier substrate
Solder layer
PowerThinGaN top viewPower thin film LED; scematic side view
Light extraction of 75% is reached
White LEDs
Phosphors
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Spontaneous vs Stimulated Emission
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Gain - LASER
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Structure of a laser diode
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Optical characteristics of Laser Diodes
LaserOptical Power
LEDOptical PowerStimulated
Optical Power
λ
Laser
λ
Optical Power
I0
λ
Ith
Spontaneousemission
Stimulatedemission
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Typical output optical power vs. diode current (I) characteristics and the correspondingoutput spectrum of a laser diode.© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
LEDs vs Laser Diodes
Light powerLaser diode
LED10 mW
)(2
)1(2
0 thph JJqn
RWhcP −
−=
λτ
Current0
LED
100 mA50 mA
5 mW JP ∝0
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Typical optical power output vs. forward currentfor a LED and a laser diode.
100 mA50 mA
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
Structure of a laser diode
L
WCleaved reflecting surface
Oxide insulator
Stripe electrode
SubstrateElectrode
p-GaAs (Contacting layer)
n-GaAs (Substrate)
p-GaAs (Active layer)
Currentpaths
L
p-AlxGa
1-xAs (Confining layer)
n-AlxGa
1-xAs (Confining layer) 12 3 Substrate
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Schematic illustration of the the structure of a double heterojunction stripecontact laser diode
Active region where J > Jth.(Emission region)
Cleaved reflecting surfaceEllipticallaserbeam
Structure of a laser diode
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Degradation of optoelectronic devices
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Critical factors for LED degradation
Defects in the
active layer
(non-rad rec., Degradation of the
Detachment of the
bonding wire
b)b)
Degradation of
ohmic contacts (non-rad rec.,
impurity
diffusion, In-
related effects)
Degradation of the
phosphorous layer
bonding wire
Aluminum plate
Browning of the lens
and package material
ohmic contacts
(Mg-related)
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Aluminum plate
Detachment from the
copper frame
Critical factors for laser diode degradation
µE-LAB,
Reliability and failure analysis of optoelectronics devices
After M. Fukuda, ESREF 2007
Optical Characteristics of LEDs and Laser Diodes
OptoelectronicOptoelectronic devicesdevices::
•High densities of injected carriers
•LEDs Light output power is nearly proportional to injected current
•Laser Diodes Above threshold optical power has a linear dependence on
Lig
ht
po
we
r
StimulatedStimulated
emissionemission High High
gaingain
Lig
ht
po
we
r
LED Laser
•Laser Diodes Above threshold optical power has a linear dependence on
injected current
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Current
SpontaneousSpontaneous emissionemission
((L~carrierL~carrier density)density)
Current
EECC
EEVV
Stress conditions for LEDs and Laser Diodes
DrivingDriving methodologymethodology
••LED LED ConstantConstant currentcurrent drivingdriving ((dimmingdimming) ) DegradationDegradation parameterparameter: : OpticalOptical powerpower
••Laser Laser ConstantConstant OpticalOptical PowerPower drivingdriving ((egeg disk disk writingwriting) ) DegradationDegradation parameterparameter: :
operatingoperating currentcurrent
LED Laser
Lig
ht
po
we
r
Gradual (slow)
Sudden
Rapid
Gradual (slow)
SuddenRapid
Cu
rre
nt
LED Laser
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Aging time
Rapid
Aging time
Degradation of Laser Diodes
SuddenSudden degradationdegradation::
DislocationDislocation growthgrowth in the in the innerinner regionregion
RapidRapid ((afterafter gradualgradual):):
Op
era
tin
gO
pe
rati
ng
Cu
rre
nt
Cu
rre
nt Stress at Stress at constantconstant
opticaloptical powerpower
RapidRapid ((afterafter gradualgradual):):
--facetsfacets (COD)(COD)
--dislocationdislocation growthgrowth in the in the activeactive regionregion
--bondingbonding damagedamage
--electrodeelectrode damagedamage
GradualGradual::
--pointpoint defectsdefects in the in the activeactive regionregion
Op
era
tin
gO
pe
rati
ng
µE-LAB,
Reliability and failure analysis of optoelectronics devices
GradualGradual::
--pointpoint defectsdefects in the in the activeactive regionregion
--facetsfacets
Stress Stress timetime
Gradual degradation of the Active Region
-
Generation of defects
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Generation of defects
A case study: degradation of the active region of Blu-Ray LDs
n-GaN Guiding Layer
InGaNInGaN/GaN MQWs/GaN MQWs
p-AlGaN e- Blocking Layer
p-GaN Contact Layer DevicesDevices characteristicscharacteristics::
•Vertical structure devices (on GaN)•Emission wavelength = 405 nm•Slope efficiency = 1.6 W/A•Threshold current density = 3.2 kA/cm2 (29 mA)
GaN substrate and buffer
AlGaN Cladding Layer
n-GaN Guiding Layer •Threshold current density = 3.2 kA/cm2 (29 mA)
Stress Stress fixturesfixtures::
•Devices mounted on Peltier fixtures•Junction-to-case thermal resistance ~ 52 K/W•Maximum self-heating during stress 15 °C
AdoptedAdopted stress stress conditionsconditions::
µE-LAB,
Reliability and failure analysis of optoelectronics devices
24
AdoptedAdopted stress stress conditionsconditions::
Fixed parameter Varying parameter
Fixed current (70 Fixed current (70 mAmA dc)dc) TemperatureTemperature in the range 30in the range 30--7070 °°CC
Fixed Fixed TTcc (180 (180 °°C)C) NNo biaso bias
Fixed Fixed TTcc (70 (70 °°C)C) Current in the range 200 µACurrent in the range 200 µA--80 80 mAmA dcdc
A typical stress setup
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Thermal characterization – Calibration phase
•Samples on a Peltier-fixture (30<T<90°C)CalibrationCalibration
Goal To evaluate junction temperature during operation
Method Xi and Schubert, Appl. Phys. Lett., 85, 2163, 2004.
•Samples on a Peltier-fixture (30<T<90 C)
•Short current pulses Voltage measurements
CalibrationCalibrationphasephase
Im (mA)
80 mA
4.2
4.4
4.6
4.8
Vol
tage
(V
)
Im=20 mA, I
m=30 mA,
Im=40 mA, I
m=50 mA,
Im=60 mA, I
m=70 mA,
Im=80 mA
µE-LAB,
Reliability and failure analysis of optoelectronics devices
26
0/)( TTmf BeAIV −+=
ExtrapolationExtrapolation ofof A, B and TA, B and T00 forfor the the calculationcalculation ofof RRthth
t
1 mA
30 40 50 60 70 80 90 1003.4
3.6
3.8
4.0
4.2
Vol
tage
(V
)
Fixture temperature TF (°C)
Thermal characterization – Rth extrapolation
••FixedFixed temperature (70 temperature (70 °°C)C)
••FixedFixed currentcurrent ((IImm))
••VoltageVoltage measurementmeasurement afterafter self self heatingheatingtransienttransient JunctionJunction temperature temperature evaluationevaluation
JunctionJunctiontemperature temperature evaluationevaluation
transienttransient JunctionJunction temperature temperature evaluationevaluation
•Rth = 52 K/W
•During stress at 70 mA,
TF=70 °C, Tj~80 °C (within 76
78
8070 mA
60 mA
50 mA
40 mA
Junc
tion
tem
pera
ture
(°C
)
Thermal resistance = 52 K/W(case temperature = 70 °C)
µE-LAB,
Reliability and failure analysis of optoelectronics devices
TF=70 °C, Tj~80 °C (within
recommended limits)
50 100 150 200 25070
72
7430 mA
25 mA
Junc
tion
tem
pera
ture
(°C
)
Joule Power = Total Power - Optical Power (mW)
20 mA
20
30
40
50 Before stress After stress
Opt
ical
pow
er (
mW
)
Threshold
L-I Characteristics before/after stress
•L-I curves measured before and after stress at 40 mA, 70 °C
AfterAfter stress: stress: •Increased Ith
•Same slope efficiency
Stress at 40 mA (4.4 kA/cm2), 70 °C,
1000 h
101
102
Opt
ical
Pow
er (
mW
)
Before stress After stress
20 25 30 35 40 45 50 55 60
0
10
Opt
ical
pow
er (
mW
)
Injected current (mA)
Threshold current increase
•Same slope efficiency
Linear scale
Semilog.
µE-LAB,
Reliability and failure analysis of optoelectronics devices
20 25 30 35 40 45 50 55 6010-2
10-1
100
Opt
ical
Pow
er (
mW
)
Injected current (mA)
Sub-thresholdemissiondecrease
Semilog.
scale•Stress induces also the decrease of
sub-threshold emission
(see semilog. plot)
Stress at 40 mA (4.4 kA/cm2), 70 °C, 1000 h
Ith increase vs OPsub decrease
1)( −=∆ th tI
I
ComparisonComparison betweenbetween::
ThresholdThreshold currentcurrent increaseincrease
0
5
10
I th in
crea
se (
%)
1)0(
−=∆th
thth I
I
)0(
)(1
sub
subsub OP
tOPOP −=∆
SubSub--thresholdthreshold OP OP decreasedecrease(at 28 (at 28 mAmA))
0 200 400 600 800 100060
70
80
90
100
0
OP
sub
varia
tion(
%)
I
Stress at 40 mA (4.4 kA/cm2), 70 °C, 1000 h
µE-LAB,
Reliability and failure analysis of optoelectronics devices
)0(subOP
The two parameters vary with the same kinetic Correlation
0 200 400 600 800 1000OP
Stress time (h)
Correlation between Ith increase and OPsub decrease
BNA +=τ1
n
Carriers recombination lifetime τ is determined
by the balance between the non-radiative (A) and
radiative (B) recombination
I is proportional to the ratio between threshold )( thth
thth BnAn
nI +=∝
τIth is proportional to the ratio between threshold
carrier density (nth) and the carriers recombination
lifetime τ
SinceSince::
•Both OPsub and Ith depend on the balance between radiative and non-radiative recombination events (τ)
µE-LAB,
Reliability and failure analysis of optoelectronics devices30
radiative recombination events (τ)•The variations of these two parameters have similar kinetics•Coefficient A is related to the defectiveness of the active layer (increasing during stress, Tomiya 2004)
Ith and OPsub variation can be attributed to the increase of the non-
radiative recombination rate A
Measurement details: τnr extrapolation
Purpose: Extrapolate non-radiative lifetime during ageing
Method: Proposed by Van Opdorp in 1981
Based on subthreshold Optical measurement
Non radiative
recombination
Radiative
recombination
Total currentLeakage current
Inj. current
Pint
electrons
Pout
p region
µE-LAB,
Reliability and failure analysis of optoelectronics devices31
recombinationPint
holes
n region
40
50
60 After 400 h
Non
-rad
. rec
ombi
natio
n ra
te (
%)
Increasing stre
ss times
τnr during stress time
Stress at 120 mA, 70 °C
Linear correlation
0 2 4 6 8 10 12
0
10
20
30
40
Non
-rad
. rec
ombi
natio
n ra
te (
%)
Before stress
Increasing stre
ss times
)( ththth BnAnI +∝
Linear correlation
between the increase in
Ith and A
0 2 4 6 8 10 12
Non
-rad
. rec
ombi
natio
n ra
te (
%)
Threshold current increase (%)
Previous reports (Tomiya2004, Marona2006) The decrease in τnr can
be correlated to the increase of the concentration of defects in the
active region of the devices
Which is the driving force for degradation?
Measurement results: Correlation of Ith and τnr
1.0
1.1
1.2
1.3
1.4
Nor
mal
ized
Par
amet
er v
aria
tion
Stress @ 4.44 KA/cm2
Ith variation
ComparisonComparison
betweenbetween::
Constant current ageing,
Fixed temperature = 70°C
Stress at 40 mA dc
0.5
0.6
0.7
0.8
0.9
1.0
τnr variation
Nor
mal
ized
Par
amet
er v
aria
tion
Stress @ 4.44 KA/cm Stress @ 6.66 KA/cm2
Stress @ 8.88 KA/cm2
Stress @ 11.1 KA/cm2
IIthth increaseincrease
ττττττττnr nr decreasedecrease
Parameters vary
according to the
Stress at 40 mA dc
Stress at 60 mA dc
Stress at 80 mA dc
Stress at 100 mA dc
µE-LAB,
Reliability and failure analysis of optoelectronics devices33
0 200 400 600 800 1000 1200 1400 1600 1800 20000.4
nr
Nor
mal
ized
Par
amet
er v
aria
tion
Stress Time (h)Ith and ττττnr are correlated during device degradation
Which is the effects of different chaning ageing current?
according to the
square root of
time
Measurement results: Effects of ageing current
The correlation is confirmed40mA 60mA
Plot of Ith increase as a function of 1/τnr
140
130
140
var
iatio
n (%
)
80mA 100mA
100 120 140 160 180 200
100
110
120
130
130
140
var
iatio
n (%
)
130
140
100 120 140 160 180 200
100
110
120
130
I th v
aria
tion
(%)
( )[ ]2/1 ththnrth BnnqVI += τ
Compatible with
trasparency condition
µE-LAB,
Reliability and failure analysis of optoelectronics devices34
The two mechanisms have the same
dependence on the driving currents
100 120 140 160 180 200
100
110
120
I th v
aria
tion
(%)
1/τnr variation (%)
100 120 140 160 180 200
100
110
120
1/τnr variation (%)
Trivellin et al, ESREF 2009
Effect of stress current on the degradation kinetics
Stress conditions:
•Case temperature=70 °C
•Stress current=200µA-80 mA
•Maximum junction temperature
= 82 °C0.5
1.0
4
6
8
80 mA
Thr
esho
ld c
urre
nt in
crea
se (
%)
60 mA
Thr
esho
ld c
urre
nt in
crea
se (
%)
Tc=70 °C
= 82 °C
Increasing stress current determines
faster degradation
•Degradation kinetics are strongly determined by the stress current level
0 50 100 150 200
0.0
0.5
0 50 100 150 200
0
2
Thr
esho
ld c
urre
nt in
crea
se (
%)
Stress time (h)
Stress at 200 µA,T
c=70 °C
40 mA
Thr
esho
ld c
urre
nt in
crea
se (
%)
Stress time (h)
20 mA
µE-LAB,
Reliability and failure analysis of optoelectronics devices35
•Degradation kinetics are strongly determined by the stress current level
•At 70 °C Threshold current is 40 mA
•Degradation occurs also below lasing threshold (and at 200 µA!), i.e. without strong
optical field and self-heating Role of current?
Degradation Rate vs Stress Current
6
8
incr
ease
afte
r 20
0 h
(%) At the stress
temperature (70 °C),
threshold current is
40 mA
In this region, stress
current is < Threshold
current
Ith = 4
0 m
A
0 20 40 60 800
2
4
I th in
crea
se a
fter
200
h (%
)
+ 0.1% / mA
40 mA
µE-LAB,
Reliability and failure analysis of optoelectronics devices
•Degradation occurs also below threshold
•Degradation rate is strongly determined by stress
current level
0 20 40 60 80
Stress current (mA)
Degradation rate = Ith
increase after 200 h of
stress
Study of the degradation of the active region by C-V measurements
p-type
Anode
n-type
Cathode
µE-LAB,
Reliability and failure analysis of optoelectronics devices
The area for the C-V
measurements is close to
500 x 75 µm2
Constant current stress – Output power during stress
Stress at 32 A/cm2
µE-LAB,
Reliability and failure analysis of optoelectronics devices
••Stress Stress conditionsconditions
85 A/cm85 A/cm22, RT (, RT (TjTj<100 <100 °° C)C)
Current ageing – Current – Voltage Characteristics
••Stress Stress conditionsconditions
85 A/cm85 A/cm22, RT (, RT (TjTj<100 <100 °° C)C)85 A/cm85 A/cm22, RT (, RT (TjTj<100 <100 °° C)C)
µE-LAB,
Reliability and failure analysis of optoelectronics devices
••Stress Stress inducesinduces significantsignificant modificationsmodifications in the in the
electricalelectrical characteristicscharacteristics ofof the the devicesdevices ((increaseincrease in in
reverse and reverse and generationgeneration--recombinationrecombination componentscomponents))
Heterostructure degradation C-V measurementsInformation about
charge distributionDepleted region
••Stress Stress conditionsconditions
85 A/cm85 A/cm22, RT (, RT (TjTj<90 <90 °° C)C)
ApparentApparent chargecharge distributiondistribution
p+-GaN n-GaN
µE-LAB,
Reliability of Reliability of GaNGaN--based optoelectronic devices: state of the art and perspectivesbased optoelectronic devices: state of the art and perspectives
••Detection Detection ofof changeschanges ofof the the
chargecharge profileprofile inducedinduced byby stressstress
••A. A. CastaldiniCastaldini, IWN 2004, IWN 2004
••PhysPhys. . StatStat. Sol. (c) 2, 2862 (2005). Sol. (c) 2, 2862 (2005)
••J. J. ApplAppl. . PhysPhys. 99, 053104 (2006). 99, 053104 (2006)
Correlation between OP loss and C-V data
••CorrelationCorrelation betweenbetween
OP OP decreasedecrease and and chargecharge
variationvariation
••ChangesChanges
in the Cin the C--V V
profilesprofiles
1.0
1.2
1.4
Con
cent
ratio
n (x
1018
cm
-3) ••LocalizedLocalized chargecharge
increaseincrease in the in the
activeactive regionregion
1.1. Stress Stress inducedinduced a a significantsignificant increaseincrease in in
the Cthe C--V curve (V curve (concentratedconcentrated in the in the
activeactive regionregion))
µE-LAB,
Reliability of Reliability of GaNGaN--based optoelectronic devices: state of the art and perspectivesbased optoelectronic devices: state of the art and perspectives
40 60 80 100 120 140 160 180 200 2200.0
0.2
0.4
0.6
0.8
Con
cent
ratio
n (x
10
Depth (nm)
Before stress After 5h After 100h
activeactive regionregion))
2.2. Strong Strong correlationcorrelation betweenbetween OP OP
decreasedecrease and and chargecharge variationvariation
3.3. DLTS DLTS analysisanalysis indicatedindicated thatthat stress stress
inducesinduces the the increaseincrease ofof a a DLDL peakpeak
((detecteddetected DLsDLs havehave EaEa in the in the rangerange
250250--900 900 meVmeV))
Correlation between OP loss and C-V data
••CorrelationCorrelation betweenbetween
OP OP decreasedecrease and and chargecharge
variationvariation
••ChangesChanges
in the Cin the C--V V
profilesprofiles
0.000
A
••DLTS DLTS analysisanalysis in in
the the activeactive regionregion1.1. Stress Stress inducedinduced a a significantsignificant increaseincrease in in
the Cthe C--V curve (V curve (concentratedconcentrated in the in the
activeactive regionregion))
µE-LAB,
Reliability of Reliability of GaNGaN--based optoelectronic devices: state of the art and perspectivesbased optoelectronic devices: state of the art and perspectives
50 100 150 200 250
-0.012
-0.008
-0.004
C
B
Untreated 2 hours 10 hours 20 hours 50 hours 100 hours
Temperature (K)
∆C/C
activeactive regionregion))
2.2. Strong Strong correlationcorrelation betweenbetween OP OP
decreasedecrease and and chargecharge variationvariation
3.3. DLTS DLTS analysisanalysis indicatedindicated thatthat stress stress
inducesinduces the the increaseincrease ofof a a DLDL peakpeak
((detecteddetected DLsDLs havehave EaEa in the in the rangerange
250250--900 900 meVmeV))
Gradual degradation
-
Degradation of the contacts
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Degradation of the contacts
A case study: degradation of the ohmic contacts of LEDs
p-Side
Anode golden pad SiN passivation
•Devices with vertical structure grown on SiC
•Bare LED chips mounted on InGaN/GaN MQW
n-Side
SiC bulk
Cathode contact
•Bare LED chips mounted on TO18 package
•LEDs covered with SiN passivation to reduce surface leakage and encapsulate the
devices
µE-LAB,
Reliability and failure analysis of optoelectronics devices
devices
•LEDs submitted to stress at high temperatures
(180<T<250 °C)
Stress of bare LED chips – OP during stress
75
100
180°CO
P m
easu
red
at 1
0 m
A
(% o
f ini
tial v
alue
)
0 500 1000 1500
25
50
190°C
210°C220°C
230°C
OP
mea
sure
d at
10
mA
(%
of i
nitia
l val
ue)
250°Cτ/100 teKI −⋅−=
µE-LAB,
Reliability and failure analysis of optoelectronics devices
0 500 1000 1500
Stress time (minutes)
IncreasingIncreasing stress temperature stress temperature determinesdeterminesstrongerstronger degradationdegradation
Stress of bare LED chips – Activation energy
103
Tim
e co
nsta
nt (
τ)
kTEt AeeKI // ,100 ∝⋅−= − ττ
21 22 23 24 25 26
101
102
Tim
e co
nsta
nt (
Ea= 1.3 eV
µE-LAB,
Reliability and failure analysis of optoelectronics devices
OP OP degradationdegradation isis thermallythermally activatedactivated(Ea=1.3 (Ea=1.3 eVeV))
21 22 23 24 25 26
q/kT
Stress of bare LED chips – L-I curves
10-1
100
Out
put p
ower
(a.
u.)
10-5 10-4 10-3 10-2 10-1
10-4
10-3
10-2
Out
put p
ower
(a.
u.)
Before stress After 90 min at 250 °C
µE-LAB,
Reliability and failure analysis of optoelectronics devices
10 10 10 10 10
Input current (A)
••OpticalOptical powerpower decreasedecrease waswas more more prominentprominent at at high high measuringmeasuring currentcurrent levelslevels
Stress of bare LED chips – Normalized L-I curves
90
100
110
Rel
ativ
e O
utpu
t Pow
er (
norm
aliz
ed)
Before stress After 90 min at 250 °C
0 5 10 15 2040
50
60
70
80-42 % OP at 1 mA
Rel
ativ
e O
utpu
t Pow
er (
norm
aliz
ed)
-56 % OP at 20 mA
µE-LAB,
Reliability and failure analysis of optoelectronics devices
••OpticalOptical powerpower decreasedecrease waswas more more prominentprominent at at high high measuringmeasuring currentcurrent levelslevels
0 5 10 15 20
Rel
ativ
e O
utpu
t Pow
er (
norm
aliz
ed)
Input current (mA)
Stress of bare LED chips – EMMI
M. Meneghini et al., IEEE TED 53 (12), 2981-2987 (2006)
Anode golden pad
p-GaN
250µµµµm
• Stress at 250 °C
• I=10 mA
Anode contact
Top view
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Before stress: uniform pattern
Before stress• I=10 mA
Stress of bare LED chips – EMMI
M. Meneghini et al., IEEE TED 53 (12), 2981-2987 (2006)
Anode golden pad
p-GaN
250µµµµm
• Stress at 250 °C
• I=10 mA
Anode contact
Top view
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Before stress: uniform pattern
• I=10 mAAfter 30 min
Stress of bare LED chips – EMMI
6
8CB
In
tens
ity(a
.u.) Before stress
AAnode golden pad
p-GaN
250µµµµm
A B C
0 25 50 75 100 125
0
2
4
6
Inte
nsity
(a.u
.)
Anode contact
Top view
µE-LAB,
Reliability and failure analysis of optoelectronics devices
0 25 50 75 100 125
X Axis (µm)
BeforeBefore stress stress UniformUniform emissionemission profileprofile in in regionsregions A and BA and B
Stress of bare LED chips – EMMI
6
8CB
In
tens
ity(a
.u.) Before stress
After 30 min
AAnode golden pad
p-GaN
250µµµµm
A B C
0 25 50 75 100 125
0
2
4
6
Inte
nsity
(a.u
.)
After 30 min After 60 min After 90 min
Passivated LEDAnode contact
Top view
µE-LAB,
Reliability and failure analysis of optoelectronics devices
0 25 50 75 100 125
X Axis (µm)
AfterAfter stress stress Strong Strong decreasedecrease ofof the light the light emissionemission in in regionregion A (far A (far fromfrom the the centralcentral pad)pad)
Stress of bare LED chips – I-V curves
15
20
Cur
rent
(m
A) D R
S
2.0 2.5 3.0 3.5 4.00
5
10
Before stress After 10 min After 40 min After 90 min
Cur
rent
(m
A)
µE-LAB,
Reliability and failure analysis of optoelectronics devices
2.0 2.5 3.0 3.5 4.0
Voltage (V)
High temperature treatment High temperature treatment determinesdetermines the the shiftshift ofof the Ithe I--V V curvescurves towardstowards higherhigher voltagesvoltages
Stress of bare LED chips – Fitting of the I-V curves
3.7
3.8
3.9
4.0
23
24
25
26
Idea
lity
fact
or n
Ser
ies
resi
stan
ce R
s (Ω
)
10
15
20
Before stress After 10 min
Cur
rent
(m
A) D R
S
0 20 40 60 80 100
3.5
3.6
21
22
Ideality factor
Idea
lity
fact
or n
Stress time (min)
Ser
ies
resi
stan
ce R
s (
Series resistance
2.0 2.5 3.0 3.5 4.00
5 After 10 min After 40 min After 90 min
Voltage (V)
RSD
nkt
RIVq
eII)(
0
−
∝
µE-LAB,
Reliability and failure analysis of optoelectronics devices
eII 0∝••RsRs IncreaseIncrease IncreasedIncreased resistivityresistivity ofof pp--GaNGaN and and
contactscontacts••n n increaseincrease DegradationDegradation ofof the the propertiesproperties ofof the ohmic the ohmic
contactscontacts
Stress of bare LED chips – Role of Passivation
••PECVD introduces H in the passivation PECVD introduces H in the passivation
layer and/or at the interface with player and/or at the interface with p--GaNGaN
••Generation of MgGeneration of Mg--H complexes H complexes Lowering of effective acceptor concentrationLowering of effective acceptor concentration
pp--GaN layerGaN layer
PassivationPassivation
HH HHHH HH HH HH HH HH HH HH
••Generation of MgGeneration of Mg--H complexes H complexes Lowering of effective acceptor concentrationLowering of effective acceptor concentration
Metal p-GaN
hh++
Ohmic contacts on pOhmic contacts on p--type GaN type GaN Tunnel junctions (very Tunnel junctions (very
high acceptor concentration) high acceptor concentration)
EEFF VBVB
AnalysisAnalysis on on TLMsTLMs Information on the Information on the effectseffects ofof stress on M/S system stress on M/S system
µE-LAB,
Reliability and failure analysis of optoelectronics devices
hh++
Metal p-GaN
Stress Stress lowerslowers activeactive dopant dopant concentrationconcentration at pat p--side side
SchottkySchottky barrierbarrier broadeningbroadening
RectifyingRectifying behaviorbehavior EEFFVBVB
••Passivation deposition introduces H in Passivation deposition introduces H in the passivation layer and/or at the the passivation layer and/or at the interface with pinterface with p--GaN (SiHGaN (SiH44 as as precursor)precursor)
HH HHHHHH
HHHH
HH
HH
HH
HH
HH
HH
HH
HH
HH HHHHHH
HHHH
••Heating at 250 Heating at 250 °°C allows this hydrogen to interact with LEDs surfaceC allows this hydrogen to interact with LEDs surfac e
Stress of bare LED chips – Role of Passivation
••S. M. Myers, J. Appl. Phys., 89, 6, 3195, 2001S. M. Myers, J. Appl. Phys., 89, 6, 3195, 2001
••C. H. Seager, J. Appl. Phys., 92, 12, 7246, 2002C. H. Seager, J. Appl. Phys., 92, 12, 7246, 2002
••Generation of MgGeneration of Mg--H complexes and/or degradation of ohmic contacts H complexes and/or degradation of ohmic contacts (worsening of transport properties)(worsening of transport properties)
µE-LAB,
Reliability and failure analysis of optoelectronics devices
••Golden pad obstructs hydrogen Golden pad obstructs hydrogen diffusion towards pdiffusion towards p--GaNGaN
••Degradation takes place mainly out of Degradation takes place mainly out of the pad regionthe pad region
••Emission is concentrated under the padEmission is concentrated under the pad
Stress of bare LED chips – Role of Passivation
100
Out
put p
ower
(%
)
••DegradationDegradation isis stronglystronglyrelatedrelated toto the the presencepresence
ofof the the SiNSiN--PECVDPECVD
0 20 40 60 80 100
40
60
80 Without passivation
With passivation
Out
put p
ower
(%
)
Stress at 250 °C
ofof the the SiNSiN--PECVDPECVDpassivation passivation layerlayer
••DuringDuring PECVD PECVD processprocess, , SiHSiH44 and NHand NH33 are are usedused
asas precursorsprecursors(passivation (passivation containscontains
µE-LAB,
Reliability and failure analysis of optoelectronics devices
0 20 40 60 80 100
Stress time (min)(passivation (passivation containscontains
hydrogenhydrogen))
Degradation of the contacts of power LEDs
Aim: characterization of the degradation of the met al/semiconductor contacts
Techniques:
•Scanning Electron Microscopy (SEM)
•Energy dispersive X-ray Spectrometry (EDS)
BackBack--scattered imagescattered image 3D reconstruction3D reconstruction
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Poor adhesion of the metal layer Poor adhesion of the metal layer Related to RRelated to R ss increase?increase?
Degradation of the ohmic contacts of LEDs
••Bare Bare InGaNInGaN LED LED chipschips havehave beenbeen submittedsubmitted toto thermalthermal storagestorage
(180<T<250 (180<T<250 °° C)C)
••OP OP degradationdegradation hashas a a nearlynearly exponentialexponential decaydecay, and , and isis correlatedcorrelated
toto emissionemission crowdingcrowdingtoto emissionemission crowdingcrowding
••ThermallyThermally activatedactivated processprocess, Ea=1.3 , Ea=1.3 eVeV
••OP OP decaydecay isis relatedrelated toto the the degradationdegradation ofof the the electricalelectrical
propertiesproperties ofof the the LEDsLEDs IncreasedIncreased RsRs, , worseningworsening ofof the the
propertiesproperties ofof the ohmic the ohmic contactscontacts, , determiningdetermining emissionemission crowdingcrowding
µE-LAB,
Reliability and failure analysis of optoelectronics devices
••DegradationDegradation isis relatedrelated toto the the presencepresence ofof PECVDPECVD--SiNSiN passivation passivation
RoleRole ofof hydrogenhydrogen in in devicesdevices degradationdegradation
••SputteringSputtering hashas beenbeen proposedproposed asas anan alternative alternative forfor passivationpassivation
Rapid degradation of the active region
-
Dark Line Defects
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Dark Line Defects
Dark line defects
•The structure of the DLDs has been the object of many studies.
Transmission Electron Microscopy (TEM) analyses of DLDs present them as
dense three-dimensional networks of dislocation loops and dipoles
•These clusters of crystal defects develop around a threading or a misfit
dislocation crossing the active layer, and are primarily found at the QW
and the neighbouring cladding layersand the neighbouring cladding layers
•Threading dislocations can be present in the
heterostructure as a consequence of the crystal
growth process. Most of the threading dislocations
emerge from the substrate and thread through the
epitaxial multilayer structure
µE-LAB,
Reliability and failure analysis of optoelectronics devices
•Misfit dislocations arise from internal stresses
associated with the differences between the lattice
parameters of the layers forming the multilayer
structure. They can also be introduced by handling
and mounting processes
Dark line defects
•DLDs appear as region of very low or even dark luminescence efficiency
•DLDs can appear as oriented dark structures in CL and EL images
•They are located in the active region and are constrained to the waveguide
regionSEMSEM
EBIC
EBIC detail
Another specimen
EL reference
EL common to COD and DLD
•EBIC images
also show a
dark constrast,
which reveals a
high charge-
trapping
µE-LAB,
Reliability and failure analysis of optoelectronics devices
EBICtrapping
efficiency in
those region
Dark line defects
•When studied by TEM DLDs appear as clusters of dislocations loops and dipoles
•The dislocation motion leading to the formation of DLDs proceeds by
Recombination-enhanced dislocation climb/glide
•Consists of an increase in the dislocation length mediated by either the
absorption or emission of point defects
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Dislocation climb in the active layer
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Dark line defects
DLDs appear as a network of dislocations and of dislocation loops, evolving from native defects at the epitaxial AlGaAs/GaAs
µE-LAB,
Reliability and failure analysis of optoelectronics devices
native defects at the epitaxial AlGaAs/GaAs interfaces under the effect of temperature (and recombination, as demonstrated years later)
Dark line defects
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Rapid degradation of the active region
-
Facet Degradation
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Facet Degradation
Facet degradation
While the lifetime of low power laser diodes is limited by gradual degradation, the
maximum optical power of high power laser diodes is mostly limited by the catastrophic
optical mirror damage (COMD). This failure consists in the destruction of the mirror
facetslight absorption at the facet
electron-hole pair --- bond breaking generation
facet oxidation
nonradiative recombination
defect increase
dislocation growth
µE-LAB,
Reliability and failure analysis of optoelectronics devices
heating
reduction of band-gap energy
catastrophic optical damage (COD)
dislocation growth
current concentrationCourtesy of Prof.
M. Fukuda
Facet degradation
The key parameters controlling the COMD are:
•the Surface Recombination Velocity (SRV);•the Surface Recombination Velocity (SRV);
•the density of defects at the facet;
•the facet treatment and coating, which partially determine the
previous parameters;
•the temperature dependence of the band gap of materials
forming the active region;
•the optical power and the current injection;
µE-LAB,
Reliability and failure analysis of optoelectronics devices
•the optical power and the current injection;
•the thermal conductivities of the different layers forming the
laser structure
Facet degradation
EBIC reveals lattice-oriented dark stripes at the “burned” mirrors
COD (Catastrophic Optical
Damage) affects the laser mirrors
SEM EBIC
µE-LAB,
Reliability and failure analysis of optoelectronics devices
detail detail
Facet degradation
Newton rings
POUT(mW)
monitor
front facet
Optical, on a nearby zone IL(mA)
IL(mA)
front facet
reference
leakydiode
Degradation after THB tests.Mechanism: detachmentof the mirror coating
optical
SEM
µE-LAB,
Reliability and failure analysis of optoelectronics devices
VL(V)
reference
EBIC
Facet degradation
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Facet degradation
Photoinduced oxidation of the facet. The watermolecules near the facet can be cracked to H+ and OH− and to further radicals by photolysis and trigger by photolysis and trigger the oxidation
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Catastrophic Degradation
µE-LAB,
Reliability and failure analysis of optoelectronics devices
ESD-related failure
µE-LAB,
Reliability and failure analysis of optoelectronics devices
ESD-related failure
µE-LAB,
Reliability and failure analysis of optoelectronics devices
ESD-related failure
µE-LAB,
Reliability and failure analysis of optoelectronics devices
ESD-related failure
µE-LAB,
Reliability and failure analysis of optoelectronics devices
ESD-related failure
Reverse-bias EL distribution
(before any ESD stress)
Micrograph after ESD failure (failed
region is indicated by an arrow)
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Sudden failure related to EOS
Poor definition of the mesa
Failure analysis by means of SEM images
Before AgeingBefore Ageing
Spike
of the mesa borders
After degradation
µE-LAB,
Reliability and failure analysis of optoelectronics devices
Catastrophic Failure
Conclusions
With this presentation we have given an introduction on the
operating principles and degradation mechanisms of LEDs and laser
diodes
Based on a number of case studies, we have presented guidelines forBased on a number of case studies, we have presented guidelines for
the investigation of:
•The degradation of the heterostructure of LEDs and laser diodes by
means of electro-optical techniques
•The analysis of the degradation of the properties of ohmic contacts
of optoelectronic devices
µE-LAB,
Reliability and failure analysis of optoelectronics devices
of optoelectronic devices
•Degradation processes related to Dark Line Defects
•The degradation of the facets of laser diodes
top related