A study of facet degradation of InGaAs quantum well lasers is reported. We tune up a Raman and photoluminescence micro-probe technique for determining the crystal structure and the temperature profile of the cladding layer, in steps of approximately 1 micrometer, with a temperature resolution better than 1 degree Kelvin. The cladding layer composition and cross- section temperature profile have been monitored during operation. A clear correlation between the facet degradation and the type of protective coating is found

Adduci, F.

Corvasce, C.

Del Guidice, M.

Ferrara, M.

Lugarà, M.

Pellegrino, S.

Re, M. G.

Scamarcio, G.

Sibilano, M.

Spagnolo, V.

Caltech Authors - Main

PROCEEDINGS OF SPIE
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Quantum-well-laser mirror
degradation investigated by
microprobe optical spectroscopy
C.  Corvasce, Vincenzo  Spagnolo, Gaetano  Scamarcio,
M.  Lugara, F.  Adduci, et al.
C.  Corvasce, Vincenzo  Spagnolo, Gaetano  Scamarcio, M.  Lugara, F.
Adduci, Michele  Ferrara, Michele  Sibilano, Sergio  Pellegrino, Massimo  del
Giudice, M. G. Re, "Quantum-well-laser mirror degradation investigated by
microprobe optical spectroscopy," Proc. SPIE 2648, International Conference
on Optical Diagnostics of Materials and Devices for Opto-, Micro-, and
Quantum Electronics,  (3 November 1995); doi: 10.1117/12.226195
Event: International Conference on Optical Diagnostics of Materials and
Devices for Opto-, Micro-, and Quantum Electronics, 1995, Kiev, Ukraine
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Quantum-Well-Laser mirror degradation investigated by micro-probe optical spectroscopy
C.Corvasce, V.Spagnolo, (*)G.Scatnarcio, M.Lugarà, F.Adduci, M.Ferrara,M.Sibilano
Dipartimento di Fisica, Umversità di Ban, 1-70126 Ban, Italy
S.Pellegrino, M.Del Giudice, M.G.Re
Alcatel Telettra, VimercateMilano, Italy
ABSTRACT
A study of facet degradation of InGaAs quantum well lasers is reported. We tune up a Raman
and photoluminescence micro-probe technique for determining the crystal structure and the temperature
profile of the cladding layer, in steps of -l rim, with a temperature resolution better than l°K. The
cladding layer composition and cross-section temperature profile have beenmonitored during operation.
A clear correlation between the facet degradation and the type ofprotective coating is found.
Keywords: diode laser, catastrophic optical damage (COD), Ranian micro-probe spectroscopy,
photoluininescence micro-probe spectroscopy
1. INTRODUCTION
Recently, quantum well lasers have attracted an increasing attention as light sourcein printers,
optical disk memories and optical communication systems. The recentadvances in growth techniques
have greatly improved the perfonnance and the reliability of quantum well laser diodes. The lifetime is
no longer limited by failures in bulk semiconductor, but mainly byfacet degradation caused by surface
defects that enhance non radiative decay rates and lead to high local heating!3 Thus, tounderstand and
characterize these thermal effects is fundamental for the development of long lifetimeand high stability
diode lasers.
in previous works, Raman spectroscopy4' and reflectance modulation techniques have been
used to study the facet temperature behaviour. Recently a photolu.minescence (PL) micro-probe
technique has been used to measure the lateral temperature profile ofGaAs-based single stripe and
broad-area diode lasers.7 In this work, we report a Ranian and PL micro-probe technique allowingus to
directly analyse the local heating and the crystal structure of the cladding layersand to determine their
temperature profile perpendicularly to the cavity axis. Differentmirror coatings have been compared.
We found a clear correlation between facet deterioration and the type of protective coating.
2. EXPERIMENTAL
The investigated samples consist of 1n022Ga078As single quantum well lasers. The lasers have
been groh by MOCVD on n-doped (001) GaAs substrate. A1GaAs and InGaP have been used as
cladding layer, as reported in table I.
360 / SPIE Vol. 2648 0-8194-202 1-2/95/$6.00
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Table I- Diode lasers structure
AlGaAs-based laser InGaP-based laser
uffer and substrate GaAs n-doped GaAs n-doped
cladding layer AL5Ga05As 1.4 mm InGaP 2mm
guide layer Al0 2Ga0 8As 550 A
GaAs 6oA
InGaAsP 1000 A
active layer 1n022Ga373M 70 A 1n022Ga078As 70 A
contact layer GaAs p-doped 2000A GaAs p-doped 2000A
Uncoated InGaP-based laser, A1GaAs-based laser with facets cleaved in air and then
coated with A1O3 and A1GaAS-based laser with facets cleaved in air, deoxidized and then coated
with A1203 have been investigated. Raman scattering and photoluminescence (PL) have been
excited at room temperature in a backscattering geometry by focusing the 5145 A line of an
laser directly onto the active region. Typical spots of '4j.un are obtained, smaller than the
cladding layer width of the investigated sample. The spectra were measured by using a
Jobin-Yvon 164000 triple spectrometer with focal length of 0.64 m. The signal was detected by
an N2-cooled CCD system. In order to avoid sample heating effects, the incident power density
was kept below 102 WIcm2.
3. RESULTS AND DISCUSSION
Figure 1 shows PL spectra generated in the AIIJ5GaO5AS cladding layer at different diode
currents. The shift of peak position of the PL as a function of the temperature has been
calibrated by probing ALJ5Ga5As and InGaP bulk samples with the same n-doping
concentration ofthe cladding layer, by varying the sample temperature with a heater. Thus, from
the shift of the peak position of the PL band, we are able to detect changes in the cladding layer
temperature smaller than 1°K.
By increasing the diode current up to the catastrophic optical damage (COD), a clear
correlation has been found between the output power and the facet temperature. In figure 2a the
output power and the cladding layer temperature shift are shown as a function of the diode
current 'd for an AIGaAS-based diode laser with non deoxidized facets. Both the temperature and
the output power increase at increasing 'd up to the COD. Similar results are obtained for the
uncoated InGaP-based lasers, except for the output power which saturate at 'd'8° and then
decreases by further increasing Id as shown in figure 2b.
Micro-Raman analysis allows us to detect any change in the crystal structure of the
cladding layer. In figure 3a and 3b Raman spectra recorded before and after the COD for a
coated AlGaAs-based and an uncoated InGaP-based sample, respectively, are reported. No
significant deterioration after the COD is observed for the coated sample. On the contrary, a
drastic change in the Raman spectrum is observed for the uncoated structure. After the COD, the
InGaP related band almost disappears, whereas the InGaAs one rises. This is due to Phosphorus
(P) desorption induced by the huge rise of the temperature at the COD. Thus the Raman analysis
suggests that while in the uncoated InGaP-based structure the COD is due to a P desorption in
the AlGaAs-based lasers the COD is probably related to a crystal deterioration ofthe inner layers
ofthe diode, i.e. guide and active layers.
SPIEVo!. 2648/361
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In figure 4 the temperature profile of the cladding layer of a coated AlGaAs-based laser
with deoxidized facets, obtained at different diode current, is shown. The layer temperature
rapidly decreases at increasing the distance (za) from the active region, demonstrating that most
of the heating damages are suffered only by a small region of the sample, centredon the active
layer.
The comparison between the temperature increases of the cladding layer, close to the
active region, in the laser diode with cleaved and coated facets and in the laser with cleaved,
deoxidized and then coated facets, clearly shows that in the latter the facets stay cooler; for
example at 'd'50 the cladding layer temperature for deoxidized and non-deoxidized facets is
T=16°K and zT=32°K, respectively (see figure 2a and 4). This can be ascribedto a reduced
incorporation ofdefects in the mirror layers.
4. CONCLUSIONS
In conclusion, we have demonstrated how the Raman and PL micro-probetecimique can
be used as a powerful tool in determining the crystal structure and temperature profile of the
cladding layer of quantum well lasers, during operation, with a spatial and a temperature
resolution of 1im and better than 1°K, respectively. A clear correlation is found between the
output power and the cladding layer temperature up to COD. Raman analysis suggests that in
uncoated InGaP-.based diodes the COD is due to P desorption induced by the high facet
temperature and in coated A1GaAS-baSed lasers is probably related to crystal deterioration of the
guide and active layer, while the cladding layer structure is nearly undamaged. The comparison
between A1GaAs-based laser with non-deoxidized and deoxidized facets clearly shows that the
latter process leads to a reduced incorporation of defects in the mirror layers.
5. ACKNOWLEDGEMENTS
This work has been partially supported by Italian CNR (Research National Council).
6. REFERENCES
(*) Present address: AT&T, Bell Laboratories, Murray Hill, NJ-07974, U.S.A..
1. T.Yuasa, M.Ogawa, K.Endo, H.Yonezu, "Degradation of (AIGa)As DH lasers due to
facet oxidation," App!. Phys. Lett. Vol. 32, issue 2, pp. 1 19-121, January 1978.
2. W.C.Tang, H.J.Rosen, P.Buchmann, P.Vettiger, D.Webb, 'Probe beam heating of
A1GaAs single-quantum-well laser facets in Raman microprobe spectroscopy," J. App!. Phys.
Vol. 62, issue 11, pp. 5930-5932, December 1990.
3. A. Moser, "Thermodynamics of facet damage in cleaved AIGaAS lasers," App!. Phys.
Lett. Vol.59, issue 5, pp. 522-524, July 1991.
4. S.Todoroki, M.Sawai, K.Aiki "Temperature distribution along the striped active
region in high-power GaA1As visible lasers," J. App!. Phys. Vol. 58, issue 3, pp. 1124-1128,
August 1985.
5. H.Brugger, P.W.Epperlein, "Mapping of local temperatures on mirrors of
GaAI/A1GaAs laser diodes," App!. Phys. Lett. Vol. 56, pp. 1049, 1990.
6. P.W.Epperlein, G.L.Bona, P.Roentgen, "Local mirror temperatures of red-emitting
(Al)GaInP quantum-well laser diodes by Raman scattering and reflectance modulation
measurements," App!. Phys. Lett. Vol. 60, issue 6, pp. 680-682, February 1992.
7. D.C.Hall, L.Goldberg, D.Mehuys, "Technique for lateral temperature profiling in
optoelectronic devices using a photoluminescence microprobe," App!. Phys. Lett. Vol. 61, issue
4, pp. 384-386, July 1992.
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-4
z
z
-4
0
111
0
Al—based Diode Laser
1.95 2.00 2.05
ENERGY (eV)
Figure. 1 . PL spectra generated in the A105Ga05As cladding layer at different diode currents
150
120
90
60
30
__ 150
120
90
60
30
0
'DIODE (mA)
Figure.2. Output power and cladding layer temperature shift as a function of diode current 'd for coated
A1GaAs-based with non deoxidized facets (a) and uncoated InGaP-based (b) diode lasers.
SPIE Vol. 2648 / 363
60 120 180 240 300
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rn
.—
Ct)z
z
z
180 240 300 360
RAMAN SHIFT (cm1)
420
Figure.3. Ramanspectra obtained before and afier the COD for coated A1GaAs-based with non deoxi-
dized facets (a) and uncoated InGaP-based (b) diode lasers.
364 ISPIE Vol. 2648
26
24
22
20
18
16
14
F' 12
10
8
6
4
2
0
—6 —4 —2 0
Figure.4. Temperature profile obtained at different diode currents 'd
for coated A1GaAs-based with deoxidized facets.
,
ia (gm) 2 4 6
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Quantum-well-laser mirror degradation investigated by microprobe optical spectroscopy

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Quantum-well-laser mirror degradation investigated by microprobe optical spectroscopy

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