1300nm-Range GaInNAs-Based Quantum Well Lasers
with High Characteristic Temperature
by Hitoshi Shimizu * , Kouji Kumada * , Seiji Uchiyama * and Akihiko Kasukawa *Long wavelength-GaInNAsSb SQW lasers that include a small amount of Sb
were successfully grown by gas-source molecular beam epitaxy (GSMBE) on a
GaAs substrate for application with peltier-free devices of access networks and vertical cavity
surface emitting lasers (VCSELs). The GaInNAsSb lasers oscillated under CW operation at 1.258µm at room temperature. A low CW threshold current of 12.4 mA and a high characteristic temperature (T0) of 157 K were obtained for GaInNAsSb lasers, which is the best result for GaInNAsbased narrow stripe lasers. Further, GaInNAsSb laser oscillated under CW conditions of over
100°C. A low CW threshold current of 6.3 mA and a high characteristic temperature (T0) of 256 K
were obtained for GaInAsSb lasers, which is also the best result for 1.2 µm-range highly strained
GaInAs-based narrow stripe lasers. As a result, GaInNAsSb lasers are very promising for realizing pertier-free access networks and VCSELs.

ABSTRACT1.

INTRODUCTION

Long wavelength lasers emitting at 1.2~1.3 µm grown on
GaAs substrates have been attracting much interest.
GaInNAs 1)~3), GaInAs quantum film (QF), GaAsSb, andInAs quantum dots (QD) have been reported to realize
this wavelength on GaAs substrates. Among the candidates, the large conduction band offset can be realized for
GaInNAs and highly strained GaInAs QF, which leads tostrong electron confinement in wells and to a high characteristic temperature (T0). The large T0 of 127~274 K 1), 2),which are much larger than the conventional long-wavelength GaInAsP/InP system, have been reported withthese materials. Therefore, a low-cost pertier-free system
for access networks can be realized using GaInNAs or
highly strained GaInAs QF lasers. Further, there areadvantages for a long-wavelength vertical cavity surface
emitting laser (VCSEL) on GaAs substrates that it can begrown monolithically on GaAs/AlGaAs DBR mirror withhigh reflectivity and high thermal conductivity, and it canutilize the mature technology of 850~980 nm VCSELs
such as AlAs selective oxidation.
However, most published results referred to broad arealaser characteristics with respect to GaInNAs and highly
strained GaInAs QW lasers, and there are few results so
far for narrow stripe lasers. The large T0 (148~204 K)
were reported on narrow stripe GaInNAs lasers, but thethreshold current (Ith) was very high (75~500 mA) 1), 2).
Recently, a GaInNAs laser with a low threshold current at* Semiconductor Research & Development Dept., Yokohama
R&D Laboratories

room temperature (Ith =11 mA) was reported 3), but thislaser has a relatively low T0 of 70~80 K 3).
To obtain 1.3 µm-GaInNAs lasers with good crystalline
quality, 1.2 µm-range GaInAs QF lasers that have strong
photoluminescence intensity have to be grown, because
nitride makes photoluminescence intensity poor.
A few 1.2 µm-range GaInAs QF lasers were reportedwith MOCVD growth 2). Although photoluminescence up to
1.224 µm was reported, 1.2 µm-range GaInAs QF lasers
have not been reported with MBE growth. GaInAs QF
lasers grown by MBE were only limited to around 1.12µm, because the longer migration length in MBE-growth isapt to cause the growth of QD in a highly strained
GaInAs/GaAs system. QF with a higher indium composition would be realized with good crystalline quality using ahigh growth rate, a low growth temperature, a high V/III
pressure ratio, and a surfactant 4). With respect to surfactants, only Te has been reported so far as the surfactant
for GaInAs/GaAs system. On the other hand, Sb is reported as a surfactant in Si/Ge and GaInNAs systems.
In this paper, we investigate highly strained GaInAs QF
and GaInNAs QF lasers that include a small amount of Sb
like a surfactant on GaAs substrates to improve the crystalline-quality by gas-source molecular-beam epitaxy(GSMBE) growth, and we studied the performance of
GaInAsSb and GaInNAsSb SQW ridge lasers. In Section
2, we discuss the effects of Sb on the photoluminescencecharacteristics of GaInAsSb and GaInNAsSb SQW. The
lasing wavelength of GaInAsSb QF lasers was increased
to 1.185 µm to keep the threshold current density of as
low as 280 A/cm2 5), which is one of the lowest ever reported for 1.2 µm-range GaInAs-based QF lasers. In Section
3, we fabricate ridge lasers and extract basic laser para-1meters such as gain coefficient, internal loss, and characteristic temperature. We report the high-performance CW
lasing characteristics of 1.26 µm-GaInNAsSb SQW lasers(Ith=12.4 mA @25°C, T0=157 K) and 1.20 µm-GaInAsSb
SQW lasers (Ith=6.3 mA @20°C, T0=256 K).

2.

GROWTH OF SQW LASERS AND EVALUATION OF BASIC MATERIAL QUALITY

2.1 Growth Conditions of GaInNAsSb SQW
We studied GaInNAsSb SQW lasers grown by GSMBE,
where the N source is a N radical generated by RF plasma cells. The lasers consisted of n-, p-GaInP cladding, ahighly strained Ga0.61In0.39N1-y1-y2Asy1Sby2 SQW active
layer (7.3 nm-thick), and 130 nm thick GaAs SCH layers
located on both sides of the SQW layer. The growth temperature of the active layer and the cladding layer was set
at 460°C, and the flux of AsH3 controlled by baratron was
set at 9x10-5 torr, and the growth rate of the well layer,
which is determined by the total flux of group III, was set
to 2.1 µm/h, and the flow rate of N2 was fixed at 0.05 ccm.
To recover the crystalline quality of the GaInNAsSb
layer, the lasers were annealed after growth at 650°C for
10 minutes in an atmosphere of N2 flow. The lasers werecapped by GaAs substrates to prevent the phosphorus
atoms from decomposing from the surface of the epitaxial

3

1.25

PL intensity
2
Wavelength (exp.)
Wavelength(cal.)

1.5

1.2

1

Wavelength (mm)PL intensity (a.u.)

2.5

0.5
0 -8
10

-7

-6

10

10

1.15

-5

10

Flux of Sb (torr)

Figure 1

PL intensity and PL wavelength against Sb flux for
GaInNAsSb/GaAs SQW.

layer. We investigated the effects of Sb on the PL characteristics. Figure 1 shows the PL intensity and the PL
wavelength against the flux of Sb. With a Sb flux of 1x10-6
torr, where PL intensity becomes largest, the compositionof SQW can be estimated as Ga 0 . 6 1 In 0 . 3 9 N 1 - y 0.016AsySb0.016 from the estimation of the condition of thebulk-GaAsSb layer. PL intensity of Ga 0.61 In 0.39 N 1-y-6 torr (λ=1.24 µm) is
0.016AsySb0.016 with Sb flux of 1x10
about one twentieth as strong as that of Ga0.65In0.35As QF(λ=1.12 µm). The wavelengths of as-grown Ga0.61In0.39As0.984Sb0.016 and as-grown Ga0.61In0.39N1-y-0.016AsySb0.016
were 1.19 µm and 1.27 µm, respectively. We estimated N
composition to be 0.44% from the wavelength shift of 80
nm. The FWHM of GaInNAsSb SQW was 23 meV, whichis almost the same value as Ga0.61In0.39AsSb SQW lasers(19 meV). Under the growth condition without Sb, FWHM
becomes over 200 meV at room temperature in this composition, so we can say that Sb is very effective for suppressing 3-D growth in this material.
To investigate the crystalline-characteristics of
GaInNAsSb SQW laser further, we studied the secondary
ion mass spectroscopy (SIMS) and TEM for a film withvarious Sb contents. Figure 2 shows SIMS for GaInNAsSb
SQW lasers with Sb flux of 1x10-6 torr, where N signal(Cs+N ion) and Sb signal (Cs+Sb ion) are shown. We calculated the integral intensity of SIMS signal from this figure, and show the relationship between the integrated
intensity of Sb and N amount and the flux of Sb in Figure
3. Sb was incorporated into the GaInNAsSb-SQW layer
with linearity up to the Sb flux of 2x10-6 torr, while theamount of N was almost constant.
Figure 4 shows TEM images for GaInNAsSb-SQW
lasers with Sb flux of 2x10-7 torr and 1x10-6 torr, respectively. The SQW with Sb flux of 2x10-7 torr shows 3-D
growth, however, the SQW with Sb flux of 1x10-6 torrshows 2-D growth. Sb seems to react in the
GaInNAs/GaAs system like a surfactant, which restricts
the formation of 3D-growth by suppressing surface diffusion caused by lowering the surface free energy.
PL intensities decrease with a Sb flux of more than
2x10-6 torr. The reason why the PL intensity decreases forthis amount of Sb could be due to defects caused byincreasing strain.

1000
600

GaInNAsSb-SQW
Sb=1x10-6 torr

Sb+Cs

Integrated counts (a.u.)

Secondary ion counts

N+Cs

100
Growth direction

10

500
GaInNAsSb SQWfrom SIMS

400
300
200

Sb signal
N signal

100

1
0

100

200

300

400

500

0
0

Depth (sec)

0.5

1

1.5

2

2.5

Flux of Sb (x10-6torr)

Figure 2

2

SIMS profile for GaInNAsSb SQW lasers with Sb fluxof 1x10-6 torr, where N signal (Cs+N ion) and Sb signal (Cs+Sb ion) are shown.

Figure 3

The integrated intensity of Sb and N in SIMS profile
against the flux of Sb.

Furukawa Review, No. 21

2002

Next, we studied the effects of annealing on the PL
characteristics for GaInNAsSb-SQW lasers, where N composition was decreased to 0.33% by decreasing the N
radical; that is, Ga0.61In0.39N0.0033As0.9807Sb0.016-SQW as
shown in Figure 5. The increase of PL intensity and theblue shift caused by annealing were observed as reported
in other papers. The annealing temperature of 550°C
almost recovered the quality of GaInNAsSb lasers and thewavelength of the lasers annealed at 550°C was 1.23 µm
and the FWHM of PL spectrum was as narrow as 23 meV.
We investigated extending the PL wavelength of
GaInAs-QW film 5 ) using the same methods as
GaInNAsSb-QW. The PL intensity becomes strongest
when Sb of 2x10-7 torr is added, which is estimated as Sb
composition of 0.32%. We obtained strong PL emissions
up to 1.17 µm, and we confirmed that Sb also reacts like asurfactant 5).
2.2 Evaluation of Broad Contact Lasers
The threshold current density (Jth) and the lasing wavelength were evaluated using broad area lasers forGa0.61In0.39As0.9968Sb0.0032 and Ga0.61In0.39N0.0033As0.9807Sb0.016 SQW lasers. The lasing spectrum was 1.185 µm
and 1.246 µm, respectively, for the lasers with a 600-µm
cavity under pulse conditions shown in Figure 6 (a), (b).
The lasing wavelength of GaInAsSb lasers is the longest
value reported for a MBE-grown GaInAs/GaAs-QF based
system to our knowledge. Figure 7 shows J th against
inverse cavity length. Jth for the lasers with 900-µm cavity
was as low as 280 A/cm2 for GaInAsSb lasers and 700
A/cm2 for GaInNAsSb lasers, respectively, which is rela-

tively low values among the ever reported results for 1.2µm-range GaInAs QF lasers 2) and 1.25~1.3 µm range
GaInNAs lasers 1)~3). Jth can be expressed as follows:
Nw Jtr
exp
Jth =
η

(

αi +

( )

1
1
ln
2L
RfRr
NwξwG03.

LASING CHARACTERISTICS OF RIDGEGaInNAsSbGaInNAsSb

2

Intensity (a.u.)

Intensity (a.u.)

GaAs

1

0
1174

1184

1194

1

0
1240

Wavelength (nm)
(a)

GaAs

GaAs

Figure 4

TEM images for GaInNAsSb-SQW lasers with Sb fluxof 2x10-7 torr (a) and 1x10-6 torr (b), respectively.

(1)

where Jtr is the transparent current density, Nw is thenumber of the well, η is the spontaneous emission efficiency at the threshold, αi is the internal loss, L is cavity
length, and Rf is the reflectivity of the front facet, Rr is thereflectivity of the rear facet, ξw is the optical confinement
factor per well, and G0 is the gain coefficient.
The refractive index (nr) for 1.185 µm- and 1.246 µmlight can be calculated as 3.47 and 3.46 for GaAs, and3.18 and 3.17 for GaInP. So, the optical confinement factor can be obtained by solving Maxwell's equation as
1.99% for GaInAsSb lasers and 1.98% for GaInNAsSb
lasers, respectively, assuming that nr for GaInAsSb and
GaInNAsSb is 3.52. The gain coefficient for GaInAsSb
lasers and GaInNAsSb lasers assuming the logarithmic
gain can be estimated as 1450 cm-1 and 1700 cm-1 by fitting the experimental data in Figure 7. G0 of GaInNAsSb
laser is about 1.2 times larger than that of GaInAsSb
laser, which is probably due to the strong electron confinement with the deeper band offset for electrons by adding
N; therefore, GaInNAsSb lasers can expect a larger T0
compared to GaInAsSb lasers.

2

GaAs

)

Figure 6

1245

1250

Wavelength (nm)(b)

The lasing spectrum for broad contact lasers with a
600-µm cavity for GaInAsSb SQW laser (a), and
GaInNAsSb SQW laser (b).

1.26

0.3

1.18

0.2

1.16
Ipl

0.15

1.14

wav

G 0 =1700cm-12

1.2

Broad contact laser
1000

Jth (A/cm )

1.22

0.25

Wavelength (µm)

PL intensity (a.u.)

1.24

G 0 =1450cm-1

1.12

Jth(GaInNAsSb)
Jth(GaInAsSb)

1.1

0.1
450

500

550

600

650

700

750

800

100
0

Anneal temperature (°C)

10

20

30

40

1/L (cm -1 )Figure 5

The effects of annealing on the PL intensities and PL
wavelength for GaInNAsSb-SQW lasers, where N
composition was decreased to 0.33%.

Figure 7

Jth against inverse cavity length for broad contact
lasers of GaInAsSb and GaInNAsSb SQW lasers.

3

100

100

80

30%/30%(Cal.)

30%/30%(Cal.)GaInAsSb
SQW lasers

30%/95%(Cal.)80

30%/95%(Cal.)

78%/95%(Cal.)
30%/30%(Exp.)60

Ith (mA)

Ith (mA)

78%/95%(Cal.)
30%/30%(Exp.)
30%/95%(Exp.)

40

60

30%/95%(Exp.)
78%/95%(Exp.)40

78%/95%(Exp.)

20

20

0

200

400

600

800

0

1000

200

400

600

800

1000

Cavity length (µm)

Cavity length (µm)

Figure 8

GaInNAsSb
SQW lasers

Ith against cavity length for GaInAsSb SQW lasers
with a facet reflectivity parameter. The lines are theoretical curves calculated using equation (2).

Figure 9

Ith against cavity length for GaInNAsSb SQW lasers
with a facet reflectivity parameter. The lines are theoretical curves calculated using equation (2).

LASERS
We fabricated ridge lasers with a reverse mesa structure.
The off-ridge was etched by selective wet etching to theinterface between n-InGaP cladding and GaAs opticalconfinement layer using a SiNx mask. A solution of tartaricacid and hydrogen peroxide was used to etch the GaAs
layers and hydrochloric acid was used to etch the GaInP
layers. The widths at the bottom of the ridge were about
4.3 µm for both types of laser.
3.1

Evaluation of Threshold Current and Laser
Parameters
Internal loss (αi) and internal efficiency (ηi) were evaluated from cavity length dependency of external differential
quantum efficiency for GaInAsSb and GaInNAsSb, and αiand ηi were estimated as 7 cm-1 and 100% for both typesof laser. Jtr/η can be solved as 150 A/cm2 for GaInAsSb
lasers and 380 A/cm2 for GaInNAsSb lasers, respectively,by fitting the experimental results in Figure 7, substituting
αi into equation (1). Jtr/η of GaInNAsSb lasers is about 2.5
times larger than that of GaInAsSb lasers, mainly becauseof the poor spontaneous emission efficiency ( η ) of
GaInNAsSb lasers. The further optimization of
GaInNAsSb QW growth conditions will improve the valueof η, which will result in a further reduction of GaInNAsSb
lasers.
The experimental I t h for GaInAsSb lasers and
GaInNAsSb lasers are plotted in Figure 8 and Figure 9,
respectively, along with the theoretical curves as a function of facet reflectivity. The threshold current (Ith) of theridge lasers can be expressed as follows:
Nw Jtrexp
Ith = WLη(( )αi + 1 ln 1
2L
RfRr
NwξwG0)+ I1L + I2

(2)

where W is the width at the bottom of the ridges, andI1L+I2 is the leakage current, in which I1 and I2 are constant values. We referred the value of I1 and I2 reported
previously in the analysis of 980 nm-InGaAs/AlGaAs SQWridge lasers. I 2 value was set to the same value thatreported in the paper (I2=0.78 mA). I1 was determined by

4

fitting the experimental threshold currents of the lasers
with cleaved facets (L=300, 600, 900 µm). I1 were determined as 1.3x10-2 mA/µm for GaInAsSb lasers and 2x10-2
mA/µm for GaInNAsSb lasers. Ith for GaInAsSb were 12.5
mA, 20 mA, and 26 mA for cavity lengths of 300 µm, 600µm, and 900 µm, respectively with pulse operation at
25°C. Ith for GaInNAsSb were 25 mA, 35 mA, and 47 mA
for cavity lengths of 300 µm, 600 µm, and 900 µm,
respectively with pulse operation at 25°C. The minimum
Ith of the short cavity lasers (L=200 µm) with high reflectivity (HR) coatings on both facets (SiO2/α-Si; 78%/95%)
exhibit values as low as 6 mA and 9.5 mA for GaInAsSb
lasers and GaInNAsSb lasers, respectively. Here, notethat I th for lasers with HR coatings (CL/HR, HR/HR)
agrees well with the theoretical curves.
The temperature dependence of light output power
against injected current (L-I) characteristics was investigated for lasers (L=300 µm, CL/95%) at pulse conditions
shown in Figure 10 (a) for GaInAsSb lasers and (b) for
GaInNAsSb lasers. The slope efficiencies at 25°C were0.46 W/A for GaInAsSb and 0.44 W/A for GaInNAsSb
lasers. The maximum oscillating temperatures were
145°C for GaInAsSb and 95°C for GaInNAsSb lasers.
Figure 11 shows the temperature dependence of Ith forthese lasers, where we can see that the characteristic
temperatures are 120 K (@25-125°C) for GaInAsSb
lasers and 111 K (@25-85°C) for GaInNAsSb lasers.
Figure 12 shows the temperature dependence of the maximum slope efficiencies for these lasers. The decreasingrate of the maximum slope efficiencies were -0.010 dB/K(@25-125°C) for GaInAsSb and -0.022 dB/K (@25-75°C)
for GaInNAsSb lasers. Although the band offset for theelectron becomes larger by adding N into the well, thetemperature dependence of L-I curves of GaInNAsSb
lasers deteriorated compared to GaInAsSb lasers. This
could be due to the poor crystalline of GaInNAsSb lasers;
therefore, further improvement can be expected by optimizing the growth conditions of the GaInNAsSb QW layer.
3.2 DC Characteristics of Ridge Lasers
The short cavity lasers (L=200 µm) with high reflection(HR) coatings on both facets (Rf/Rr=78%/95%) were test-

Furukawa Review, No. 21

2002

1
L=300 µm, 30%/95%

GaInAsSb SQW
L=300 µm
30%/95%
Pulsed∆T=10°C

6

Pulsed

425°C∆ Sd max = -0.022dB/K(@25-75°C)

2
145°C

GaInNAsSbGaInAsSb

0
0

10

20

30

40

50

0.1
20

60

40

8

80

100

120

140

160

Figure 12 The temperature dependence of slope efficiency for
GaInAsSb and GaInNAsSb SQW lasers under pulse
operation (L=300 µm, 30/95%).

GaInNAsSb SQW
L=300 µm
30%/95%
Pulsed∆T=10°C

660

Temperature (°C)

Current (mA)

42
GaInNAsSb SQW Laser
L=200µm, 78%/95%
CW, ∆T=10°C

25°C
2
95°C
0
0

10

20

30

40

50

60

Current (mA)

Figure 10 The temperature dependence of light-current characteristics for GaInAsSb lasers (a), and GaInNAsSb
lasers (b) under pulsed operation (L=300 µm,
30/95%).

1

25°C

3

1.5

0
1195

1245

1295

Wavelength (nm)

0.5
115°C

0
0

5

10

15

20

25

30

Current (mA)

Figure 13 The temperature dependence of light-current characteristics for GaInNAsSb lasers under CW operation(L=200 µm, 78/95%). The inset shows lasing spectrum at room temperature.

100
L=300 µm
30%/95%
Pulsed1.5

Output power (nW)

Output power (mW)

Output power (mW)

∆ Sd max = -0.010dB/K(@25-125°C)

Sd max (W/A)

Output power (mW)8

Ith(GaInNAsSb)
Ith(GaInAsSb)

Ith (mA)

T0 (@25-85°C)=111K

T0 (@25-125°C)=120K
10
20

40

60

80

100

120

140

160

Temperature (°C)

Figure 11 The temperature dependence of threshold currents
for GaInAsSb and GaInNAsSb SQW lasers underpulsed operation (L=300 µm, 30/95%).

ed under CW operation. Figure 13 shows the temperaturedependence of the light-current characteristics for
GaInNAsSb lasers. The low Ith of 12.4 mA at 25°C was
obtained under CW operation, which is almost the samevalue with the best results reported for narrow stripe
lasers 3), 6). The lasing wavelength is 1.258 µm as shown in
the inset of Figure 13. A large T0 of 157 K was obtained in
the range of 25-85°C while keeping Ith low; therefore, thisis the best result for GaInNAs-based edge emission lasers
with the low Ith and the large T0 to our knowledge 3), 6).
Further, a relatively high slope efficiency of 0.22 W/A at
25°C, a superior decreasing rate of the maximum slope
efficiency of -0.014 dB/K (@25-85°C), and a CW oscillat-

ing at more than 100°C were obtained.
GaInAsSb lasers (L=200 µm, 78/95%) were also tested
under CW operation. The lasing wavelength of GaInAsSb
laser is 1.20 µm at 20°C, and the lasers show lower Ith(6.3 mA@20°C) and higher T0 (256 K@20~70°C) compared to GaInNAsSb lasers, and it is also the best resultfor 1.2 µm-range highly strained GaInAs-based narrow
stripe lasers 6 ) . From these results, we can say thatGaInNAsSb QF lasers are very promising for realizing
peltier-free access networks and VCSELs.

4.

CONCLUSIONSLong wavelength-GaInNAsSb SQW lasers that include asmall amount of Sb, were successfully grown on GaAs
substrates by GSMBE. We confirmed that Sb reacts in ahighly strained GaInAs/GaAs system and a
GaInNAs/GaAs system like a surfactant, which increases
the critical thickness at which the growth mode changes
from 2-dimentional (2-D) growth to 3-dimentional (3-D)
growth. Low CW Ith (12.4 mA) with high T0 (157 K) andoscillation over 100°C were obtained for 1.26 µm
GaInNAsSb SQW ridge lasers, and low CW Ith (6.3 mA)
with high T0 (256 K) was obtained for 1.20 µm GaInAsSb

5

SQW ridge lasers. Both types of laser produced the best
results ever reported for GaInNAs-based edge emission
lasers and highly strained GaInAs-based edge emission
lasers with low I t h and high T 0 to our knowledge.
GaInNAsSb QF lasers are very promising for realizing
peltier-free access networks.

ACKNOWLEDGMENT
The authors would like to thank Mr. J. Kikawa for his
encouragement throughout this study. Further, we also
acknowledge Dr. M. Yokozeki, Dr. S. Yoshida, Dr. Y.
Hiratani, and Mr. T. Kurobe for their helpful discussions on
RF-GSMBE growth.

REFERENCES
1) M. Kondow et al., Jpn. J. Appl. Phys., vol. 35, p. 5711, 1996.
2) S. Sato et al., IEEE Photon. Technol. Lett., vol. 11, p. 1560, 1999.
3) S. Illek, Electron. Lett., vol. 36, p. 725, 2000.
4) M. Copel et al., Phys. Rev. Lett., vol. 63, p. 632, 1989.
5) H. Shimizu et al., Electron. Lett., vol. 36, p.1379, 2000.
6) H. Shimizu et al., Electron. Lett., vol. 36, p.1701, 2000.

Manuscript received on May 25, 2001.

6

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2002