High performance Ga As Sb ∕ Ga As quantum well lasers
S.-Q. Yu, D. Ding, J.-B. Wang, N. Samal, X. Jin, Y. Cao, S. R. Johnson, and Y.-H. Zhang
Citation: Journal of Vacuum Science & Technology B 25, 1658 (2007); doi: 10.1116/1.2781531
View online: http://dx.doi.org/10.1116/1.2781531
View Table of Contents: http://scitation.aip.org/content/avs/journal/jvstb/25/5?ver=pdfcov
Published by the AVS: Science & Technology of Materials, Interfaces, and Processing
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High performance GaAsSb/ GaAs quantum well lasers
S.-Q. Yu,a兲 D. Ding, J.-B. Wang, N. Samal, X. Jin, Y. Cao, S. R. Johnson, and Y.-H. Zhang
Center for Solid State Electronics Research, Department of Electrical Engineering, Arizona State
University, Tempe, Arizona 85287-6206

共Received 19 April 2007; accepted 13 August 2007; published 13 September 2007兲
GaAsSb/ GaAs quantum wells 共QWs兲 with 1.3 ␮m light emission are grown using solid-source
molecular beam epitaxy. The growth temperature is optimized based on photoluminescence 共PL兲
linewidth and intensity and edge-emitting laser 共EEL兲 threshold current density; these
measurements concur that the optimal growth temperature is ⬃490 ° C 共⬃500 ° C兲 for
GaAsSb/ GaAs QWs grown with 共without兲 GaAsP strain compensation. High performance EELs
and vertical-cavity surface-emitting lasers 共VCSELs兲 are demonstrated using the
GaAsSb/ GaAs/ GaAsP strain compensated active region. One EEL achieved an output power up to
0.9 W with thresholds as low as 356 A / cm2 under room temperature pulsed operation, while
another achieved continuous-wave 共cw兲 operation at temperatures up to 48 ° C for wavelengths as
long as 1260 nm. A set of VCSELs achieved room temperature cw operation with output powers
from 0.03 to 0.2 mW and lasing wavelengths from 1240 to 1290 nm. The temperature
characteristics of these devices indicate that the optimal gain-peak cavity-mode tuning for pulsed
operation specifies a room temperature PL peak redshift of 20– 30 nm relative to the cavity mode.
© 2007 American Vacuum Society. 关DOI: 10.1116/1.2781531兴

I. INTRODUCTION
Vertical-cavity surface-emitting lasers 共VCSELs兲 operating at 1.3 ␮m are of great interest for low-cost data transmission applications such as fiber to the home, local area
networks, and free-space optical interconnects. As the preferred substrate for 1.3 ␮m VCSELs, GaAs permits the
growth of near lattice-matched GaAs/ AlGaAs distributed
Bragg reflectors 共DBRs兲, which have superior optical and
thermal properties when compared to other III-V DBRs. Furthermore, the fabrication of GaAs based 1.3 ␮m VCSELs
can take full advantage of the industrial standard 850 nm
VCSEL fabrication technology, which is attractive from a
manufacturing point of view. GaAsSb quantum wells 共QWs兲
have been shown to be one of the most suitable candidates
for 1.3 ␮m active regions on the GaAs substrate.1–12
The growth of high quality GaAsSb QWs using molecular
beam epitaxy 共MBE兲 can be challenging.13–15 GaAsSb QWs
are highly strained 共⬃2.7% 兲 at the composition necessary to
achieve 1.3 ␮m emission. The strain not only limits the
maximum QW number that can be grown without misfit dislocations but also results in the strain-driven in-plane composition fluctuations that cause inhomogeneous linewidth
broadening14 and reduce internal quantum efficiency. Moreover, the growth of mixed group-V materials requires additional calibration work since the group-V species 共As and
Sb兲 have a less than unity sticking coefficient that varies with
both growth temperature and the relative flux of each
group-V element. The quality of GaAsSb/ GaAs QWs for
1.3 ␮m light emission can be improved by introducing
GaAsP strain compensation layers and further optimizing the
growth conditions of the resulting five-layer QW system.14
a兲

Author to whom correspondence should be addressed; electronic mail:
yushq@asu.edu

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J. Vac. Sci. Technol. B 25„5…, Sep/Oct 2007

As a result, high internal quantum efficiency edge-emitting
lasers 共EELs兲 and high power VCSELs have been demonstrated using this active region structure.8,11,12,16
Realizing GaAsSb/ GaAs based VCSELs can be challenging because a nearly flat conduction band alignment between
GaAs and GaAsSb results in the weak confinement of electrons and the strong confinement of holes and a less than
ideal electron-hole wave function overlap that limits
gain.15,17 Furthermore, the combination of limited gain and
in-plane composition fluctuations bring about a significant
blueshift in the gain peak under injection.16 This is an important design concern, as the key to good VCSEL performance
is the excellent alignment of the gain peak and the cavity
mode at the operating temperature. In designing a VCSEL, it
is convenient to establish this alignment based on a wavelength difference between the room temperature active region photoluminescence 共PL兲 peak and the cavity mode. For
GaAs and InGaAs active materials, the gain-peak position is
governed by thermal effects and is insensitive to band filling
under high injection. Therefore, the design rule for GaAs or
InGaAs VCSELs is to have the room temperature PL peak
slightly blueshifted relative to the cavity mode.18–20 In which
case, the active region heats up under continuous-wave 共cw兲
operation, and since the gain-peak redshift with temperature
exceeds that of the cavity mode, the gain peak and cavity
mode are aligned at the operating temperature. However, the
design rule for GaAsSb VCSELs is not as straightforward
since in addition to the thermal induced redshift, there is a
substantial gain-peak blueshift due to band filling under high
injection.
This article studies the issues related to the optimization
and growth of 1.3 ␮m, strain compensated GaAsSb/
GaAs/ GaAsP QW structures for laser applications, including
the performance characteristics of high power, cw, room

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©2007 American Vacuum Society

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Yu et al.: High performance GaAsSb/ GaAs quantum well lasers

FIG. 1. Calculated wavelength of the first energy transition in a
GaAsP / GaAs/ GaAsSb/ GaAs/ GaAsP 共9 / 5 / 7 / 5 / 9 nm兲 five-layer QW
structure as a function of Sb composition.

temperature EELs and VCSELs, and the competing effects of
a thermally induced redshift and an injection induced blueshift on the design rules of GaAsSb based VCSELs.
II. STRAIN COMPENSATED GaAsSb QWs
The critical layer thickness for pseudomorphically
strained GaAs0.6Sb0.4 on GaAs is approximately 7 nm;21
critical layer thickness not only limits the thickness of each
QW, it also limits the total number of QWs that can be consecutively grown. The latter can be overcome by adding tensile strain layers between the QWs, for which GaAsP is
readily available and as well offers enhanced electron confinement when placed either side and near to the
GaAsSb/ GaAs QW. In this work, a five-layer
GaAsP / GaAs/ GaAsSb/ GaAs/ GaAsP strain compensated
QW system is developed. The ground-state transition wavelength for this five-layer system with layer thicknesses
9 / 5 / 7 / 5 / 9 nm is calculated using the transfer-matrix
method and plotted as a function of Sb mole fraction in Fig.
1. The material parameters used for GaAs1−xSbx are linearly
interpolated between those of GaAs and GaSb except the
formula for the band gap of unstrained bulk GaAs1−xSbx,
which has a substantial bowing parameter and is given by17
Eg共x兲 = 1.43共1 − x兲 + 0.73 − 1.58x共1 − x兲.

共1兲

The Sb mole fraction is ⬃0.36 for the light emission at
1.3 ␮m.
The materials studied in this work are grown by solidsource molecular beam epitaxy using a VG V80H system
equipped with As, Sb, and P valved crackers to control the
mixed group-V composition of the active layers. To calibrate
the composition of GaAsSb layers, two sets of GaAsSb PL
samples are studied. These samples contain the above mentioned five-layer QW system, with a 50 nm thick GaAs space
layer on either side, that is sandwiched between two 50 nm

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thick Al0.25Ga0.75As barrier layers, all of which is grown on
top of a 400 nm thick GaAs buffer on a n+-GaAs 共100兲 substrate and capped by a 30 nm thick GaAs layer. The GaAs
buffer and cap and AlGaAs barriers are grown at 590 ° C and
the substrate temperature is ramped down 共up兲 without interruption during the growth of the first 共second兲 50 nm GaAs
spacer to the much lower 490 ° C growth temperature of the
active region.
The V/III flux ratios 共FAs/Ga and FSb/Ga兲 used during the
GaAsSb layer growth are FAs/Ga = 0.90, with FSb/Ga varying
from 0.2 to 0.4 for the first set of PL samples, and FAs/Ga
= 1.0, with FSb/Ga varying from 1.0 to 5.0 for the second set
of PL samples. The flux ratio used here is the ratio of the
group-V flux rate over the group-III flux rate where both are
in units of atoms per unit area per unit time. The GaAs
growth rate was 15 nm/ min and the P flux ratio was fixed
during the growth of the GaAsP layers in both sets of PL
samples. The Sb mole fraction of the GaAsSb active region
is determined from the PL peak position and is plotted as a
function of FSb/Ga and FAs/Ga in Fig. 2共a兲. The power law
equation,
xSi = 关a共FAs/Ga兲b/共FSb/Ga兲c + 1兴−1 ,

共2兲

is fit to the data 共see solid curves兲, where xSb is the Sb mole
fraction of the GaAs1−xSbx layer, FAs/Ga and FSb/Ga are the
As/ Ga and Sb/ Ga flux ratios, and a, b, and c are fitting
parameters whose values are listed in the inset of Fig. 2共a兲.
Similarly, three sets of GaAsP PL samples with a GaAsP
QW sandwiched between two AlGaAs barriers were grown
at various V/III ratios 共FP/Ga and FAs/Ga兲 to calibrate the
GaAsP composition; the P mole fraction as function of FP/Ga
and FAs/Ga is shown in Fig. 2共b兲. Equation 共2兲 共with FSb/Ga
replaced by FP/Ga兲 is fit to the data 共see solid curves兲 and the
fitting parameters are listed in the inset of Fig. 2共b兲. These
parameters provide insight into the incorporation efficiency
of the two group-V elements during the growth of mixed
As–Sb and mixed As–P ternaries. Of the three fitting parameters in Eq. 共2兲, a and c are similar and b is larger than c for
both GaAsSb and GaAsP; this result indicates that As incorporates more efficiently than either P or Sb. Furthermore, the
difference between b and c for GaAsSb is much greater than
that for GaAsP, indicating that Sb does not compete nearly as
efficiently with As as P does.
The growth temperature of the active region is further
optimized by comparing the room temperature PL peak intensity, PL linewidth, and pulsed threshold current density of
broad-area EELs with triple-QW active regions 共without
GaAsP strain compensation兲 that were grown at various substrate temperatures. A plot of the measurement results versus
growth temperature is shown in Fig. 3. All three curves, PL
peak intensity 共upper plot兲, PL linewidth 共middle plot兲, and
threshold current density 共lower plot兲, concur that the optimal growth temperature is ⬃500 ° C. Similar growth studies
indicate that the optimal growth temperature for the fivelayer,
strain
compensated,
GaAsP / GaAs/ GaAsSb/
GaAs/ GaAsP QW system is ⬃490 ° C. The introduction of
GaAsP strain compensation layers to GaAsSb/ GaAs QWs

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Yu et al.: High performance GaAsSb/ GaAs quantum well lasers

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FIG. 3. EEL wafer PL intensity 共upper plot兲, PL linewidth 共middle plot兲, and
threshold current density 共lower plot兲 versus GaAsSb QW growth
temperature.

FIG. 2. 共a兲 Sb mole fraction versus Sb/ Ga and As/ Ga flux ratios for MBE
grown GaAs1−xSbx alloys. 共b兲 P mole fraction versus P / Ga and As/ Ga flux
ratios for MBE grown GaAs1−xPx. The solid curves are fits of Eq. 共2兲 to the
data; the fitting parameters are listed in the table shown in each plot.

can reduce the PL linewidth by up to a factor of 2,14 indicating that the addition of strain compensation substantially reduces the strain-driven Sb segregation.
III. HIGH POWER, ROOM TEMPERATURE,
CONTINUOUS-WAVE EDGE-EMITTING LASERS
Two high performance EEL devices, labeled A and B, are
studied; these devices utilize strain compensated GaAsSb
QWs grown under optimized growth conditions. The
active region of device A 共B兲 is a single 共triple兲
QW
GaAs0.9P0.1 / GaAs/ GaAs0.7Sb0.3 / GaAs/ GaAs0.9P0.1
with 8 / 3 / 7 / 3 / 8 nm 共9 / 5 / 7 / 5 / 9 nm兲 thicknesses. The
nominal Sb concentration is 30%, a value estimated from PL
measurements and modeling. The active region in device A is
sandwiched between two 78 nm thick Al0.20Ga0.75As layers,
followed by two 150 nm thick linearly graded AlGaAs lay-

ers, with Al mole fractions of 25%–65%, to form a gradedindex 共GRIN兲 waveguide, followed by a Si-doped 共2
⫻ 1018 cm−3兲, 1.8 ␮m thick, n-type Al0.65Ga0.35As cladding
layer and a 500 nm thick GaAs buffer layer on the substrate
side and a Be-doped 共2 ⫻ 1018 cm−3兲, 1.8 ␮m thick, p-type
Al0.65Ga0.35As cladding layer and a 100 nm thick GaAs contact layer on the surface side. The doping concentration is
decreased from 2 ⫻ 1018 to 1 ⫻ 1017 cm−3 in both the p and n
GRIN layers and is increased to 2 ⫻ 1019 cm−3 in the
p-contact layer. Device B has a similar structure, except that
the active region is sandwiched between two 20 nm
Al0.25Ga0.75As layers and both the p- and n-type
Al0.65Ga0.35As cladding layers are 2 ␮m thick.
The devices are fabricated using photolithography and inductively coupled plasma etching to define stripe ridges,
ranging from 4 to 32 ␮m wide. By etching down to about
0.1 ␮m above the active region, these ridges provide current
confinement as well as optical waveguiding. A photoresist
mask is used to define the ridges, which also serves as a
lift-off mask for the deposition of an Al2O3 isolation layer.
This procedure ensures that a self-aligned contact window is
exposed after lift-off. Wide Ti/ Pt/ Au p-contact stripes are
deposited using a second mask, after which the wafers are
lapped down to 100 ␮m thick and AuGe/ Ni/ Au n-metal
contacts are deposited on the back side of the substrate; this
is followed by rapid thermal annealing of both metal contacts. The wafers are cleaved to form EELs with various
cavity lengths. The as-cleaved devices are mounted junction
side up onto a temperature variable test stage. Room temperature pulsed measurements are performed using a 0.5 ␮s
wide pulse and a 0.1% duty cycle. The power output is measured using a calibrated power meter equipped with an
InGaAs detector and an integration sphere. Laser spectrum

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FIG. 5. L-I curve of a GaAsSb/ GaAs QW EEL cw operating at 20 ° C with
a 935 ␮m cavity length and a 16 ␮m ridge width. Inset 共a兲: threshold lasing
spectrum at 25 ° C. Inset 共b兲: threshold lasing wavelength as a function of
temperature.

FIG. 4. Characterization results of a GaAsSb QW EEL with an 878 ␮m
cavity length and a 32 ␮m ridge width. 共a兲 Pulsed L-I curve 共single facet兲.
共b兲 Electroluminescence and lasing spectra.

measurements are performed using a 200 ␮m core diameter
multimode fiber to couple the light into an ANDO 6315A
optical spectrum analyzer.
A typical power-current 共L-I兲 curve for device A 共single
QW兲 with an 878 ␮m cavity length and a 32 ␮m stripe
width is given in Fig. 4共a兲. The device is driven by currents
up to 2500 mA. The maximum output power is
0.45 W/facet, for a total 0.9 W output. The device has a
threshold current 共Ith兲 of 100 mA, which corresponds to a
low threshold current density 共Jth兲 of 356 A / cm2. The small
kink in the curve near 2000 mA is attributed to a detector
measurement artifact due to a slow switching response during autoscaling. The emission spectra below threshold at
0.3Ith and 0.6Ith and just above threshold at 1.1Ith are given in
Fig. 4共b兲; the luminescence peak blueshifts from 1228 nm at
0.3Ith to1205 nm at 0.6Ith and to 1190 nm at 1.1Ith. Temperature dependent threshold current measurements between 0
and 85 ° C exhibit a characteristic temperature of 60 K,
which is close to previous reported results for this material
system.5–7,10,12,16 Further temperature dependent device characterization work for this material system is reported in Ref.
16.
A typical cw L-I curve at 20 ° C for device B 共triple QWs兲
with a 935 ␮m cavity length and a 16 ␮m stripe width is
given in Fig. 5; the power output measurements were limited
by the detector to a maximum of 2 mW. The lasing threshold
current density was 1.27 kA/ cm2. The 25 ° C lasing spec-

trum slightly above threshold is shown in Fig. 5, inset 共a兲.
This device exhibited a cw laser output up to 48 ° C with
wavelengths as long as 1260 nm. The threshold lasing wavelength increases from 1217 nm at 5 ° C to 1260 nm at 48 ° C
关see Fig. 5, inset 共b兲兴. This device also exhibits a significant
blueshift under lasing operation; the room temperature PL
peak wavelength is 1291 nm. This is the first reported
GaAsSb/ GaAs QW EEL with room temperature cw operation in the vicinity of 1.3 ␮m.
IV. ROOM TEMPERATURE CONTINUOUS-WAVE
VCSELs
Top-emitting VCSELs utilizing the triple five-layer strain
compensated GaAsSb/ GaAs/ GaAsP QWs were also studied. In these devices, the active region is placed at the center
of a one ␭ cavity that is between the upper DBR of 23 pair
Be-doped p-type Al0.9Ga0.1As/ GaAs layers and the bottom
DBR of 30.5 pair Si-doped n-type Al0.9Ga0.1As/ GaAs layers.
A 50 nm thick p-type AlAs oxidation layer is placed 3␭ / 4
away from the cavity center in the p-DBR. Reflectance measurements were used to characterize the cavity mode of the
as-grown wafer. PL measurements were performed by first
etching away the top DBR so that the 514 nm Ar+ laser can
directly pump the active region. The VCSELs were fabricated using standard photolithography and wet etching to
define square 共120⫻ 120 ␮m2兲 mesas. The mesa etch went
down through the p-DBR layer and was stopped 0.1 ␮m
above the active region to expose the oxidation layer. Selective wet oxidation of the AlAs layer was performed in a
steam environment to form an ⬃5 ⫻ 7 ␮m2 current confinement aperture. A Ti/ Au p contact was deposited on top of
the mesa and a AuGe/ Ni/ Au n contact was deposited on the
back side of the substrate. Finally, the devices were annealed
at 400 ° C for 30 s to form Ohmic contacts.
The devices were tested under cw operation at room temperature and exhibited peak powers ranging from
0.03 to 0.2 mW at wavelengths ranging from 1290 to

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Yu et al.: High performance GaAsSb/ GaAs quantum well lasers

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FIG. 6. GaAsSb VCSEL L-I-V curve; the lasing spectrum at 1.1 times
threshold is shown in the upper-left inset; the near field lasing profile is
shown in the lower-right inset.

1240 nm, respectively, depending on where the device was
located on the wafer. Figure 6 shows the light-currentvoltage 共L-I-V兲 characteristics and lasing spectrum 共upperleft inset兲 at 1.1 times threshold. The threshold current,
turn-on voltage, and peak power are 3.7 mA, 1.5 V, and
0.18 mW, respectively. The ripples in the L-I curve are due
to the optical feedback from the polished back side of the
substrate. A three-dimensional near field image is shown in
the lower-right inset of Fig. 6 and indicates that this VCSEL
operates in a high order mode.
Three VCSELs labeled C, D, and E were studied with
respective PL peak and lasing cavity-mode wavelengths of
1278 and 1260 nm 共18 nm PL redshift兲, 1266 and 1285 nm
共19 nm PL blueshift兲, and 1291 and 1260 nm 共31 nm PL
redshift兲 共see Table I兲. The lasing cavity-mode wavelengths
are estimated from the cw lasing wavelengths. The device
characteristics were determined using temperature dependent
pulsed L-I measurements over a 0 – 90 ° C range. The lasing
threshold current versus temperature exhibits very different
tuning characteristics for these three VCSELs; the results are
given in Fig. 7 for device C 共upper plot兲, device D 共middle
plot兲, and device E 共lower plot兲. For device C, the threshold
current increases slightly as the temperature increases from
0 to 60 ° C and the threshold increases steeply from
60 to 80 ° C. For device D, the threshold current decreases
from 0 to 80 ° C. For device E, the threshold decreases from
0 to 10 ° C, is constant from 10 to 60 ° C, and increases
from 60 to 90 ° C.

TABLE I. Summary of device PL peak, cavity mode, and PL peak redshift to
cavity mode for devices C, D, and E.

VCSEL
C
D
E

PL peak
共nm兲

Cavity mode
共nm兲

PL peak redshift to
cavity mode 共nm兲

1278
1266
1291

1260
1285
1260

18
−19
31

FIG. 7. Pulsed threshold current versus heat-sink temperature for three different GaAsSb QW VCSELs.

V. DISCUSSION
For the GaAsSb/ GaAs material system, the gain peak is
substantially blueshifted relative to the PL peak under injection due to strong band filling and inhomogeneous Sb
composition,16 which is confirmed by the EEL results reported above. The different VCSEL threshold temperature
characteristics shown in Fig. 7 are attributed to a combination of this blueshift and different initial gain-peak cavitymode alignments; all devices tested were grown using the
same recipe and processed back to back, and therefore similar electrical characteristics are expected. The room temperature PL peak relative to the cavity mode for devices C and E
is redshifted by 18 and 31 nm, respectively. Consequently,
the blueshift during lasing moves the gain peak toward the
cavity mode, resulting in a low, temperature insensitive,
threshold region from 10 to 60 ° C where the gain peak and
the cavity mode are nearly aligned. Conversely, the room
temperature PL peak relative to the cavity mode for device D
is blueshifted by 19 nm. Consequently, the blueshift during
lasing moves the gain peak even further away from the cavity mode, resulting in a high, temperature sensitive, threshold
that continually improves from 0 to 90 ° C as the thermal
redshift continually moves the gain peak toward the cavity
mode. These results indicate that the room temperature PL
peak should be redshifted by 20– 30 nm relative to the cavity
mode for optimal pulsed performance. However, under cw
operation, it is estimated that the active region temperature is
⬃40 ° C higher than the heat-sink temperature, causing a
redshift of ⬃15 nm and a correspondingly reduced PL peak
redshift for best room temperature cw performance.
The gain-peak blueshift also contributes to the high order
transverse mode operation shown in the lower-right inset of
Fig. 6. For oxide confined VCSELs, there are two distinct
cavity modes: one at the longer wavelengths specified by the
as-grown cavity length that lies within the oxide aperture and

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Yu et al.: High performance GaAsSb/ GaAs quantum well lasers

one at the shorter wavelengths specified by the shorter cavity
length in the region outside the oxide aperture, where the
high refractive index AlAs layer has been converted to a low
refractive index 共optically thinner兲 Al2O3 layer. The spatial
distribution of the modal gain at longer wavelengths conforms to the oxide aperture profile, which tends to support
the single fundamental mode, provided that the aperture size
is small 共typically 10⫻ 10 ␮m2 for GaAs or InGaAs based
VCSELs兲, while at shorter wavelengths the profile is ringlike, which tends to support high order transverse modes.
Therefore, when the peak modal gain at shorter wavelengths
is larger 共due to the above mentioned blueshift兲, the high
order transverse mode will prevail 共assuming the same optical losses for both modes兲. For the VCSEL shown in Fig. 6,
the room temperature PL peak was close to the cavity mode,
resulting in a blueshifted misalignment of the gain peak and
cavity mode during lasing operation; this is expected to be
the reason why this device exhibits a high order transverse
modal behavior even though the oxide aperture is small.
These distinctive gain properties of the GaAsSb material
system require a different design rule for VCSELs. In order
to have good gain-peak cavity-mode alignment during room
temperature lasing, it is essential that the room temperature
PL peak be at substantially longer wavelengths than the cavity mode.
VI. CONCLUSIONS
The MBE growth of GaAsSb containing active regions is
optimized by performing temperature dependent photoluminescence intensity, linewidth, and threshold current density
measurements on edge-emitting lasers. The optimal growth
temperatures are found to be 490 ° C for strain compensated
GaAsSb/ GaAs/ GaAsP active regions and 500 ° C for
GaAsSb/ GaAs active regions. High performance edgeemitting lasers and vertical-cavity surface-emitting lasers are
demonstrated using the strain compensated active region.
The edge emitters demonstrated power outputs up to 0.9 W
and threshold current densities as low as 356 A / cm2 under
pulsed operation and wavelengths as long as 1260 nm at
temperatures up to 48 ° C under cw operation. All edge-

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emitting lasers displayed a strong gain-peak blueshift under
high injection. The oxide confined VCSELs demonstrated
room temperature cw operation with power outputs from
0.03 to 0.2 mW and lasing wavelengths from 1240
to 1290 nm. A room temperature PL peak redshift of
20– 30 nm relative to the cavity mode provides the best
pulsed operation performance for GaAsSb VCSELs.
ACKNOWLEDGMENT
This work is partially supported by the National Science
Foundation under Grant No. 0070125.
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