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Reliability investigations Lifetime measurements anddegradation mechanisms
Bernd Sumpf, Ute Zeimer, Karl Häusler, Andreas KlehrFerdinand-Braun-Institut für HöchstfrequenztechnikGustav-Kirchhoff-Straße 4, D-12489 Berlin, Germany
Jens W. TommMax-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie BerlinMax-Born-Str. 2 A, D-12489 Berlin, Germany
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
OutlineI. Aging tests for high power diode lasers
1. Degradation measurements: tasks and objectives2. Statistical basics, acceleration factors3. Experimental set-up4. Aging test – selection of samples, accompanying measurements 5. Statistical analysis of results
II. Analytical work for understanding gradual degradation mechanisms: Strain measurement
1. Approach and Definitions2. Theory 3. Experimental methods and results
3.1 Micro-Photoluminescence (µPL) 3.2 Photocurrent spectroscopy (PCS)3.3 Degree-of-polarization PL or R (DoP-PL)
4. Summary
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Aging tests for high power diode lasers
1. Degradation measurements: tasks and objectives
2. Statistical basics, acceleration factors
3. Experimental set-up
4. Aging test – selection of sample, accompanying measurements
5. Statistical analysis of results
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Degradation measurements: tasks and objectives
• Degradation MeasurementsDefined aging of the diode laserAccompanying diagnostic measurements to understand aging
• Aim of the measurementQualification of laser diode structureLong term stability of
- Epitaxial structure- Surfaces- Contacts- Facets
Estimation of life time of the laser diodeSuggestions for the improvement of the structure
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Aging tests for high power diode lasers
1. Degradation measurements: tasks and objectives
2. Statistical basics, acceleration factors
3. Experimental set-up
4. Aging test – selection of sample, accompanying measurements
5. Statistical analysis of results
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Statistics: reliability – definitions
Reliability= Probability of a reliable operation until time t.
Failure probability:= Probability for a device failure until time t.
Mean time to failure (MTTF)= Expectation of failure time.
)(tR
)(1)( tRtF −=
dttdt
tdFMTTF )(0∫∞
=
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Statistics: assumption – exponential distribution
)exp(-)( ttR ⋅= λReliability:
Failure probability:λ: Failure rate = const. („hazard failure rate“)
Mean time to failure:
Example:Demanded reliability R = 0.98 over an operating time
top = 4 years (35040 h)
)exp(--1)( ttF ⋅= λ
)ln(-1 op
Rt
MTTF ==λ
h107.1 6⋅=MTTF
MIL-HDBK-217F, 6.13 „Optoelectronics, Laser Diode“, 6-21 (1991)
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Design of experiments – unknown failure time
Determination of the failure probability of samples:
n – number of test samples in the lotr – number of samples with failure within the testF – failure probability – unknown value
Solution: Beta-distribution
∫−+
=F
n-rr xxxrrn
nFB0
d)-1(!)!(
1)!()(
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Design of experiments – unknown failure time
Assuming a certain confidence level (1 - α)
Determination of α−=−+
= ∫ 1d)-1(!)!(
1)!()(0
Fn-rr xxx
rrnnFB
0.0 0.2 0.4 0.6 0.8 1.00.0
0.2
0.4
0.6
0.8
1.0n = 5r = 1
F
Confidence level1−α = 0.6
B(F
, r+1
, n−r
+1)
Beta-distribution for n = 5 and r = 1i.e.: 5 samples in test, 1 failure
B(F, r + 1, n − r + 1) = 0.6
⇒ F = B0.6(r +1, n − r +1)
e.g. F = B0.6 (2;5) = 0.309
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Design of experiments – unknown failure time
Calculation of the MTTF:
Aging time of the experiment: taging = 10000 h (417 days)
60% probability that the MTTF ≥ MTTF0.60Under nominal conditions requested MTTF not verifiable!
⇒ Accelerated lifetime tests
)]1,1( - [1lnMTTF
-1
aging1 +−+
−=− rnrBt
αα
h27055].3090 - [1ln
h10000MTTF1 =−=−α
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Reasons for degradation
Point defects, DislocationsAbsorb the laser light and convert it into heatMove during operation and accumulate in the active region
recombination enhanced defect motion – REDM-process
Facet degradationBand gap deformation within the cleaved facetsAbsorption and non-radiative recombination – COD
Local stressLocal changes in the band gap – absorption and heatingPoint defects - recombination enhanced defect reaction – REDR
Processes accelerated at high power and high temperature
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Acceleration factors
Overstressing of devices to proof longer lifetimes by• Higher output power, i.e. higher current• Higher temperature
Failure rate for accelerated lifetime test:
op: operational conditionsaging: conditions of the aging test
πT: acceleration factor caused by temperatureπI: acceleration factor caused by higher currentπP: acceleration factor caused by higher output power
PITopaging πππλλ ⋅⋅⋅=
MIL-HDBK-217F, 6.13 „Optoelectronics, Laser Diode“, 6-21 (1991) and Bellcore GR-468-CORE Iss. 1 (1998)
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Acceleration factor – temperatureTemperature:
Activation energy Ea = 0.3 - 0.5 eVempirical value, different values from literature
Heating during operatione.g. at Rth = 10 K/W; Popt = 10 W; ηC = 0.5
temperature increase of about 100 K
⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛−=
opaging
aT
11-expTTk
Eπ
⎟⎟⎠
⎞⎜⎜⎝
⎛−⋅=∆ 11
cth η
PRT
MIL-HDBK-217F, 6.13 „Optoelectronics, Laser Diode“, 6-21 (1991) and Bellcore GR-468-CORE Iss. 1 (1998)
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Acceleration factors – power and currentPower:
Derating exponent β = 2 … 6; P – optical power
CurrentCoefficient x = 0 … 2
β
π ⎟⎟⎠
⎞⎜⎜⎝
⎛=
op
agingP P
P
x
op
agingI ⎟
⎟⎠
⎞⎜⎜⎝
⎛=
II
π
MIL-HDBK-217F, 6.13 „Optoelectronics, Laser Diode“, 6-21 (1991) and Bellcore GR-468-CORE Iss. 1 (1998)
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Example – accelerated lifetime test
Target MTTF ≥ 1.7 Mio hAssumption: EA = 0.5 eV, β = 2.3, x = 0; 1− α = 0.6; n = 5; taging = 10000 h
Conditions of the accelerated test: Paging = 2 x Pop and Taging = 65°C; Top = 25°C
πT x πP = 66, i.e. 66 times increase of the failure rate
Number of failures r = 0, 1 or 2:To detect the target MTTF – only one diode out of five is allowed to fail !
]-6 1,(-ln[1-h10000MTTF
6.06.0 rrB
TP+
××=
ππ
r MTTF0.6
0 4.3 x 106 h1 1.8 x 106 h2 1.0 x 106 h
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Aging tests for high power diode lasers
1. Degradation measurements: tasks and objectives
2. Statistical basics, acceleration factors
3. Experimental set-up
4. Aging test – selection of sample, accompanying measurements
5. Statistical analysis of results
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Experimental set-up: Requirements
• Measurement of degradation rates below 10-5 h-1
Accuracy better than 1% within 1000 h
- Assumption 1 A current, 10 mA changes in 1000 h
- in 24 h changes of 0.24 mA
- 10 bit resolution of 1 A: 0.976 mA
- 12 bit resolution of 1 A: 0.244 mA
- 16 bit resolution of 1 A: 0.015 mA
Aging tests at temperatures 15°C ≤ T ≤ 80°C for more than 1000 h
- Temperature stability better 0.1 K
No degradation of the set-up
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Experimental set-up: Test Environment
• Test chambers with stabilized temperature• Measurement of power between 100 mW … 15 W with high accuracy
Challenge: attenuation of power- RW laser diodes: emission power up to P = 500 mW,- High-power BA laser diodes up to P = 15 W- Laser bars P ≥ 100 W
• Computer controlled current supply and measuring system• Selection criteria for devices:
Power-voltage-current characteristicsFacet inspectione.g. longitudinal mode analysis
• Failure analysise.g. cathodoluminescence
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Experimental set-up
Geometrical attenuation of lightin test chamber
Test Chamber
LiTHERMTemperature
Controller15°C ≤ T ≤ 75°C
Photodiode Laserdiode
Current supplye.g. Thorlabs - Profile
LDC 80808 A
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Experimental set-up
Test chamber for five laser diodes
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Experimental set-up
Test chamber
Temperature controller
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Attenuation of light withan integrating sphereExperimental set-up
GPIB
MotionController
Currentsupply
Power meter
travelling detector
40 laser diodes at 8 banks
Current andmotion controller,e.g. Newport
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Experimental set-up
Electronics
Aging boxwith integrating sphere inside
Holder for 5 laser diodes
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Experimental set-up
SM35-45
Test Chamber
TemperatureController
15°C ≤ T ≤ 75°C
Power meter
Measurement of optical power with a detector
capable to measure 100 We.g. Gentec
LaserdiodeCurrent supply
e.g. delta electronica
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Experimental set-up 19" Rack system
Test chamber
Heat sinksHolderfor detector
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Aging tests for high power diode lasers
1. Degradation measurements: tasks and objectives
2. Statistical basics, acceleration factors
3. Experimental set-up
4. Aging test – selection of sample, accompanying measurements
5. Statistical analysis of results
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Selection of samples
0.0 0.4 0.8 1.20
100
200
300
400
500
Out
put p
ower
P /
mW
Current I / A
before aging
Power-current-characteristics:• Selection of devices• Definition of operational current
Example:9 devices; λ = 650 nmGeometry: 100 µm x 750 µmT = 15°C
Measurement before 10000 h of aging test
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Selection of samples
Measurement of near field(optional)
• Detection of facet failures
Example:650 nm device100 µm x 750 µm; T = 15°C, P = 500 mW
Near Field: Top-hat shape; W1/e2 = 100 µm
-100 -50 0 50 100
rela
tive
inte
nsity
/ ar
b. u
nits
position x / µm
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Selection of samples
Measurement of near field(optional)
• Detection of facet failures
Example:730 nm tapered laser2.75 mm longT = 25°C, P = 2 W
Near Field: W1/e2 = 160 µm
-200 -100 0 100 200re
l. in
tens
ity /
arb.
uni
ts
position x / µm
Facet failure
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Selection of samples
60 µm
Visual inspection of the facet:
Example 650 nm BA-laser60 µm x 750 µm
Electroluminescence image:• Current below threshold• Optical microscope 60 µm
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Selection of samples
Visual inspection of the facet:
Example 650 nm BA-laser60 µm x 750 µm
Electroluminescence image:• Current below threshold• Optical microscope
• Failure in the IR Image
60 µm
60 µm
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Selection of samples
Analysis of the longitudinal mode spectrumSpacing of longitudinal
modes ∆λ depends on Wavelength λLaser length LRefractive index n
Defect change local refractive indexFormation of sub-cavitiesModulation of the envelope of the mode spectrum
Crystal defect
Lzdz
0
Front-facet
Rear-facet
Measurement of spectrum below thresholdFourier-Transformation delivers position of defect
gnL ⋅⋅=∆
2
2λλ
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Selection of samples
Analysis of the longitudinal mode spectrum – simulation
Mode-Spectrum of a laser diode with L = 1 mm Defects at 125 µm and 350 µmmeasured from front facet
Fourier-Transformation of Mode spectrum
1010 1015 1020 1025 10300
2
4
6
8 R = 10-4
Pow
er P
/ arb
. uni
ts
Wavelength λ / µm
0 2 4 6 8 100.00
0.05
0.10
1000µm
∆ = 3.06µm
348.6µm128.5µm
Position inside the cavity / arb. units.
Am
plitu
de /
arb.
uni
ts
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Aging test - 650 nm DQW broad area lasers
100 µm x 750 µmReliable operation at T = 15°C
400 mW (4 mW/µm): 9(9) - t = 1000 h
500 mW (5 mW/µm): 7(9) - t = 10000 hMTTF – 40000 h No COD failures
Lifetime sufficient for medical applications (1000 h)and close to the demands for display application ( > 10000 h) 0 2500 5000 7500 10000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
500 mW
400 mW
Cur
rent
I / A
Aging time t / h
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Measurements after aging test
Power-current-characteristics:• Test of devices• Comparison with aging result
Example:Nine 650 nm devicesGeometry: 100 µm x 750 µmT = 15°C
Measurement after 10000 h of aging test
All devices still operational.No COD-Failures
0.0 0.4 0.8 1.20
100
200
300
400
500
Out
put p
ower
P /
mW
Current I / A
before aging after aging
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Measurements after aging test
Device without degradation
before 10000 h aging test
after 10000 haging test
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Aging test - 650 nm DQW broad area lasers
100 µm x 750 µmReliable operation at T = 15°C
600 mW (6 mW/µm): 7(7) - t ≥ 1100 h
Lifetime sufficient for medical applications (1000 h)
0 1000 20000.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Cur
rent
I/ A
Aging Time t / h
600 mW at 15°C
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Measurements after aging test
Device with degradation
before aging test
after aging test Defects
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Cathodoluminescence (CL): Principle• Penetration depth of
electron beamabout 3 µm
• Generation of electron-hole-pairs
• Radiative recombination
• At defectsnon-radiativerecombination
Measurements:• Spectra• Images
Lateral resolution ≤ 1 µmSpectral resolution ≤ 0.5 nm
Electron beam, UB : 5 - 35 kV
Sample, T = 80 K
Monochromator
Detector
Electronics,Monitor
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Preparation of samples for CL
• Unsoldering from mount
• Grinding of the n-side metallization
• Wet chemical removal of GaAs substrate
Thickness of sampleabout 3 – 4 µm
CuW
CuW
CuW
AuSubstrateEpi-Layers
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
CL-measurement: facet failure930 nm,10 W, 25°C, 3700 h, 100 µm stripe width
850 855 860 865 870 875 880
0
1x105
2x105
3x105
4x105
5x105
6x105
outside stripe front facet centre rear facet
Inte
nsity
/ ar
b. u
.
λ / nm
∆λ = ± 1 nm
SE-image
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
CL-measurements: Internal defects I
934.0 934.5 935.02
4
6
8
920 930 940 9500
2
4
6
8
10
pow
er p
/ a.
u.wavelenghtλ / nm
T = 25°Cλmax = 933.79nmL = 4000µm
pow
er P
/ a.
u.
wavelength λ / nm 0 1000 2000 3000 40000.00
0.01
0.02
0.03
90µm
2928µm1063µm
position inside cavity / µm
ampl
itude
/ a.
u.
100 µm 100 µm
Analysis of the longitudinal mode spectrum – comparison with CL
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
CL-measurements: Internal defects II980 nm, 8 W, 25°C, 2410 h, 100 µm stripe width
EL-image facet
100 µm
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
CL-measurements: Internal defects III
[110] – DLDs (dark line defects)
15° - branching in [112] – direction
Confined to stripe
No DSDs (dark spot defects)
930 nm, 8 W, 25°C, 1400 h, 100 µm stripe width
No facet damage, electroluminescence image without failure
[110]
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Aging tests for high power diode lasers
1. Degradation measurements: tasks and objectives
2. Statistical basics, acceleration factors
3. Experimental set-up
4. Aging test – selection of sample, accompanying measurements
5. Statistical analysis of results
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Statistical analysis
Input: • n devices per lot• r failures are observed• Assumption: exponential distribution of failure function • Total test time t• Failure time for the failed diode ti
• α-quantile of χ2-function χ2α:
2/)22(
)(
:level confidence 1
)(1
:likelihoodmaximum
21
1
1
+
+−=
−
+−==
∑
∑
=−
=
r
ttrnMTTF
rttrn
MTTF
rj j
rj j
αα
χ
α
λ
Ref: Reliability and Degradation of Semiconductor Lasers and LEDs,M. Fukuda, Artec House, 1991
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Aging test - 650 nm DQW broad area lasers
100 µm x 750 µmReliable operation at T = 15°C
400 mW (4 mW/µm): 9(9) - t = 1000 h
500 mW (5 mW/µm): 7(9) - t = 10000 hMTTF – 40000 h No COD failures
Lifetime sufficient for medical applicationsand close to the demands for display application 0 2500 5000 7500 10000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
500 mW
400 mW
Cur
rent
I / A
Aging time t / h
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Statistical analysis
Maximum likelihood estimation:Aging experiment – 500 mW, total test time t = 10000 h• 9 devices per lot; 2 failures are observed• Assumption: exponential distribution of failure function • Failure time for the failed diode tj: 3703 h, 9041 h
h413722
h) 9041 h (3703 h10000)29(
)(1 1
=++⋅−
=
+−==
∑ =
MTTF
rttrn
MTTFrj j
λ
Ref: Reliability and Degradation of Semiconductor Lasers and LEDs,M. Fukuda, Artec House, 1991
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Statistical analysis
1−α confidence level:Aging experiment – 500 mW, total test time t = 10000 h• 9 devices per lot; 2 failures are observed• Assumption: exponential distribution of failure function • Failure time for the failed diode tj: 3703 h, 9041 h
[ ] h266936.2
h9041h3707 h10000)29(2
2/)22(
)(
6.0
21
1
=++⋅−⋅
=
+
+−=
∑ =−
MTTF
r
ttrnMTTF
rj j
αα
χ
Ref: Reliability and Degradation of Semiconductor Lasers and LEDs,M. Fukuda, Artec House, 1991
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Aging test - 650 nm DQW broad area lasers
100 µm x 750 µmReliable operation at T = 15°C
600 mW (6 mW/µm): 7(7) - t ≥ 1100 h
Lifetime sufficient for medical applications
0 1000 20000.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Cur
rent
I/ A
Aging Time t / h
600 mW at 15°C
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Statistical analysis
Maximum likelihood estimation:Aging experiment – 600 mW, 2377 h: • 7 devices per lot; 7 failures are observed• Assumption: exponential distribution of failure function • Failure time for the failed diode ti: 1175 h, 1328 h, 1800 h, 1822 h,
1822 h, 2309 h, 2377 h
h18057
h 2377)23091822182218001328(1175
)(1 1
=++++++
=
+−==
∑ =
MTTF
rttrn
MTTFrj j
λ
Ref: Reliability and Degradation of Semiconductor Lasers and LEDs,M. Fukuda, Artec House, 1991
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
Statistical analysis
Maximum likelihood estimation:Aging experiment – 600 mW, 2377 h: • 7 devices per lot; 7 failures are observed• Assumption: exponential distribution of failure function • Failure time for the failed diode ti: 1175 h, 1328 h, 1800 h, 1822 h,
1822 h, 2309 h, 2377 h
[ ] h150616.8
h23772309182218221800132811752
2/)22(
)(
6.0
21
1
=++++++⋅
=
+
+−=
∑ =−
MTTF
r
ttrnMTTF
rj j
αα
χ
Ref: Reliability and Degradation of Semiconductor Lasers and LEDs,M. Fukuda, Artec House, 1991
Tutorial - WWW.BRIGHT.EU Plenary Meeting – 5. & 6. July 2006, Cambridge, UK
SummaryLifetime measurements for laser diodes and bars
Deliver:• Information on quality of materials, processes, mounting, etc.• Hints for the improvement of technology• Data for reliable lifetime of devices, MTTF, reliability
Require:• Enough experimental data• Statistical analysis of data• Highly stable measurement set-up• Accompanying measurements• Non-destructive failure analysis• Destructive failure analysis