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Electronics Letters, 41, 2, pp. 71-72, 2005-01-20
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1.53µm GaInNAsSb laser diodes grown on GaAs(100)
Gupta, J. A.; Barrios, P. J.; Zhang, X.; Pakulski, G.; Wu, X.
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1.53 m GaInNAsSb laser diodes
grown on GaAs(100)
J.A. Gupta, P.J. Barrios, X. Zhang, G. Pakulski and X. Wu
GaInNAsSb=GaNAs double quantum well ridge waveguide laser
diodes with room temperature lasing wavelength of 1532 nm are
reported. The devices exhibit leakage-corrected threshold current
densities as low as 969 A cm
2
per quantum well in pulsed mode,
with characteristic temperatures as high as 90 K.
Introduction: In the past decade, GaInNAs vertical cavity and edge-
emitting laser diodes ha v e been used for 1.3 mm emission with promising
results
[1]. Although early efforts at wav elengths suitable for long-haul
fibre transmission yielded devices with very high laser threshold currents
[2, 3], the most recent devices ha v e had more reasonable characteristics.
These latest devices have used GaInNAs
[4] or GaInN AsSb [5, 6] active
regions, producing emission in the 1.5 mmrange.
In this Letter we present results of GaInNAsSb=GaNAs double
quantum well lasers with record lasing wavelength of 1532 nm. The
structures were grown by molecular beam epitaxy (MBE) using a novel
method of Ar gas dilution in a radio frequency (RF) plasma to control
the active nitrogen flux for MBE growth. Narrow, single-lateral-mode
ridge waveguide (RWG) devices were tested in pulsed mode and exhibit
threshold currents as low as 115 mA (w ¼ 3 mm) at room temperature
(RT), while wider (w ¼ 10 mm) devices exhibit high characteristic
temperatures of 90 K. After accounting for lateral leakage current, the
threshold current densities for sets of devices with cavity lengths of
1202 and 444 mm were found to be 1.94 and 2.66 kA cm
2
. These
results provide clear confirmation of the promise of GaInNAsSb active
regions for GaAs-based 1550 nm laser diodes.
Fabrication: The lasers w ere grown on an n þ GaAs substrate in a custom
VG V90 MBE system. Flux es were pro vided by group-III and dopant
effusion cells with valved cracker cells for As
2
and Sb
2
. Active nitrogen w as
pro vided by a VEECO RF plasma source using N
2
=Ar dynamic
gas switching, as described previousl y
[7]. The active region, grown at
415
C, nominally consists of two 7 nm Ga
0.61
In
0.39
N
0.027
As
0.962
Sb
0.011
quantum we lls with 20 nm GaN
0.044
As
0.956
barriers, within a 371 nm GaAs
waveguide. 1.5 mmAl
0.33
Ga
0.67
As:Be (1 10
18
cm
3
) and 1.8 mm
Al
0.33
Ga
0.67
As:Si (2 10
18
cm
3
) cladding layers were grown at 600
C.
After each 97 nm of n-cladding growth, a 3 nm GaAs:Si la y er was grow n
to smooth the surface. The top 100 nm GaAs:Be contact la yer was doped to
1 10
19
cm
3
, while the bottom GaAs:Si buffer la y er was doped to
2 10
18
cm
3
. Before fabrication, the wafer was annealed at 700
C, for
300 s under flowing N
2
with GaAs proximity capping.
RWG lasers were fabricated using chemically-assisted ion beam
etching with standard Ti-Pt-Au and Au-Ge-Ni p- and n-contact metal-
lisations, respectively. The lasers were cleaved into bars with Fabry-
Perot cavity lengths of 1202, 894 and 444 mm and mounted p-side up
onto alumina carriers. Each bar contains devices with ridge widths from
2to10mm. Measurements were made in pulsed mode with a 1% duty
cycle and the output power was measured using a calibrated Ge
detector. The emission spectra were measured using an optical spectrum
analyser.
Results:
Fig. 1 shows the light output wi th input curre nt (L–I )curve
for a nar row, 2 mm-wide RWG d evice wi th cavity length 1202 mm.
The RT threshold current was found to be 157 mA with stimulated
emission wavelength near 1532 nm at low current injection, as shown.
Temperature-dependent measurements of this device yi elded a charac-
teristic temperature, T
0
,of66K,whilea10mm-wide device with the
same cavity length exhibited T
0
¼ 90 K. The lowest threshold current
measured in this s tudy was 115 mA f or a nar row RWG d evice
measuring 3 by 444 mm, and the same device exhibited the highest
external differential efficiency, Z
D
,of35%.
The lateral leakage current in these devices was estimated using the
method of
[8]. Fig. 2 shows the dependence of threshold current on
ridge width for the complete set of devices. For each cavity length, the
leakage current was determined from the expression I
th
¼ J
th
wL þ I
leak
,
via a linear regression of the data in
Fig. 2 for widths longer than 4 mm.
The narrowest devices (2 and 3 mm) were excluded because these
dimensions are close to the estimated carrier diffusion length. Note
that this analysis yields a single value of threshold current density for
each cavity length, as well as the leakage current estimate.
Fig. 1 Light output per facet (L) against applied current (I) for laser diode
(width 2 mm, length 1202 mm)
Inset: Spectrum at 165 mA (1.05I
th
)
Fig. 2 Threshold current (I) dependence on ridge width for several cavity
lengths as indicated
Fig. 3 Inverse differential quantum efficiency dependence on cavity length
for 5 and 9 mm ridge widths as indicated
For device widths of 5 and 9 mm, the internal quantum efficiency, Z
i
,
and internal loss, a
i
, were determined from Fig. 3. For the 5 mm-wide
devices we found Z
i
¼ 0.66 0.13 and a
i
¼ 25 7cm
1
, while the
9 mm-wide devices had Z
i
¼ 0.61 0.07 and a
i
¼ 29 5cm
1
.
In
Fig. 4 we plot the relationship between threshold current density,
J
th
, and cavity length. The current density for infinite cavity length was
ELECTRONICS LETTERS 20th January 2005 Vol. 41 No. 2
found to be 806 A cm
2
per quantum well, and for devices of width
5 and 9 mm, the transparency current densities were J
tr
¼ 317 A cm
2
and 282 A cm
2
, using the internal parameters determined earlier.
Fig. 4 Threshold current density dependence on inverse cavity length
Conclusion: We have demonstrated 1.53 mm emission from
Ga InNAsSb RWG laser d iodes with relatively low threshold currents.
To our knowledge, this is the longest lasi ng wavelength achieved
for GaInNAs(Sb) lasers on GaAs substrates. Future work will focus
on refinement of the las er design to improve the internal parameters
and optimise the devices for 1.55 mm.
Acknowledgments: The authors are g rate ful for th e technical supp or t
ofP.Chow-Chong,G.I.Sproule,R.Wang,M.Beaulieu,M.Bresee
and helpful discussio ns with Z.R. Wasilewski.
# IEE 2005 28 October 2004
Electronics Letters o nline no : 20 05762 3
doi: 10.1049/ el:2 00576 23
J.A. Gupta, P.J. Bar r ios, X. Zhan g, G. Pakulski and X . Wu (Institute
for Microstructural Sc iences, Nation al Research Counc il of Canada ,
Ottawa, Canada K1A 0R6 )
E-mail: james.gupta@nrc.ca
X. Zhang: Also with the Sc hool of Information Technology and
Engineering, University of Ottawa, 800 King Edward Ave., Ottawa,
Canada K1N 6N5
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ELECTRONICS LETTERS 20th January 2005 Vol. 41 No. 2