The gain spectra of multilayer quantum-well heterostructures on the basis of GaInAs/GaInPAs and
GaInAsSb/AlGaAsSb compounds have been analyzed. The possibility of implementing of wide and almost flat
spectrum of modal gain in the near IR range upon inhomogeneous excitation of quantum wells in such compounds
is shown

Belyavskii, V. S.

Manak, I. S.

Ushakov, D. V.

English

Электронная библиотека БГУ

ISSN 1062-8738, Bulletin of the Russian Academy of Sciences: Physics, 2008, Vol. 72, No. 2, pp. 243–245. © Allerton Press, Inc., 2008.
Original Russian Text © I.S. Manak, D.V. Ushakov, V.S. Belyavskii, 2008, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2008, Vol. 72, No. 2, pp. 262–
264.
 
243
 
Laser Diodes with a Wide Flat Modal Gain Spectrum 
in the (1–3)-
 
µ
 
m Range
 
I. S. Manak, D. V. Ushakov, and V. S. Belyavskii
 
Belarussian State University, ul. Nezavisimosti 4, Minsk, 220030 Belarus
e-mail: manak@bsu.by
 
Abstract
 
—The gain spectra of multilayer quantum-well heterostructures on the basis of GaInAs/GaInPAs and
GaInAsSb/AlGaAsSb compounds have been analyzed. The possibility of implementing of wide and almost flat
spectrum of modal gain in the near IR range upon inhomogeneous excitation of quantum wells in such com-
pounds is shown.
 
DOI: 
 
10.3103/S1062873808020275
 
Laser diodes operating in the wavelength range 1–
3 
 
µ
 
m are necessary to develop high-efficiency fiber
optical communication and data transfer systems, as
well as perform environmental monitoring, and precise
long-range optical measurements. Injection lasers on
multilayer asymmetric quantum-well (QW) hetero-
structures based on the GaInPAs and GaInAsSb quater-
nary compounds are most promising for solving the
noted problems. Such lasers provide a wide modal gain
spectrum and make it possible to implement optical
units with different lasing frequencies and the same las-
ing power.
It is well known that the transmission spectrum of
the atmosphere has transparency windows in the ranges
1.2–1.3, 1.55–1.7, and 2–2.3 
 
µ
 
m, as well as fairly effec-
tive transparency bands at wavelengths of 2.3–2.5 and
2.85–3 
 
µ
 
m [1]. At the same time, the laser radiation
decay coefficient in a quartz fiber at 
 
λ
 
 = 1.27 
 
µ
 
m is
about 0.2 db nm
 
–1
 
, while germanate glass 
 
GeO
 
2
 
 doped
with antimony oxide 
 
Sb
 
2
 
O
 
3
 
 and free of OH hydroxyls,
transition-metal ions, and other foreign impurities pro-
vides a line attenuation of 0.1 db nm
 
–1
 
 in the wave-
length range 1.8–2.5 
 
µ
 
m [2]. These characteristics
should be taken into account in design of two-color
optical units based on GaInPAs and GaInAsSb com-
pounds and operating in the (1–3)-
 
µ
 
m range.
In QW heterostructures, the wavelength corre-
sponding to radiative interband transitions, depends on
the thickness and composition of the active and barrier
layers. Therefore, individual QWs in such structures
amplify radiation in different wavelength ranges.
Selective doping of barrier layers with donor or accep-
tor impurities is performed to provide conditions for
inhomogeneous QW excitation [3, 4]. Then, the total
gain spectrum of a multilayer heterostructure with
inhomogeneously excited active layers can cover a
fairly wide wavelength range.
By the example of AlGaAs/GaAs compounds, it
was previously shown that there are several techniques
for obtaining asymmetric multilayer QW heterostruc-
tures [3, 4]. The active layers of a structure may have
different thicknesses, composition, and order of
arrangement with respect to each other and to the emit-
ters.
The gain spectra of the structures based on the GaIn-
PAs and GaInAsSb quaternary compounds are ana-
lyzed and a possibility of implementing a wide flat
modal gain spectrum in these compounds is demon-
strated here. In the case of the former compound, the
calculations were performed for an asymmetric QW
heterostructure with three or four QWs of different
thickness, generating in the (1.3–1.6)-
 
µ
 
m band. The
 
Ga
 
0.17
 
In
 
0.83
 
As
 
0.4
 
P
 
0.6
 
 compound was used for barrier lay-
ers, and the QW material was 
 
Ga
 
0.45
 
In
 
0.55
 
As
 
. The
parameters of the active and barrier layers were chosen
according to [5], so as to match the lattice constants; the
semiconductor was chosen to be direct-gap, with a band
gap corresponding to the interband transitions in the
range 1.3–1.6 
 
µ
 
m.
For these QW heterostructures in calculation of the
band energy diagram, it is necessary to take into
account the effect of hole-state mixing; therefore, the
energy levels and the wave functions of the valence
band were calculated within the approximation of the
four-band 
 
kp
 
 method [6].
The characteristics of heterostructures with QWs of
different width are considered in this study. The active
region of a heterostructure consisted of three or four
QWs with the widths 
 
d
 
1
 
 = 4
 
 nm, 
 
d
 
2
 
 = 9
 
 nm, 
 
d
 
3
 
 = 14 nm,
and 
 
d
 
4
 
 = 5 nm. The QWs were chosen so as to make the
wavelengths of the optical transitions of electrons to the
heavy- and light-hole levels in different QWs to be
slightly spaced and overlap the desired wavelength
range.
 244
 
BULLETIN OF THE RUSSIAN ACADEMY OF SCIENCES: PHYSICS
 
      
 
Vol. 72
 
      
 
No. 2
 
      
 
2008
 
MANAK et al.
 
The difference 
 
∆
 
F
 
 in the Fermi quasi-levels of QWs
of different thickness was optimized to obtain a wide
and almost flat total spectrum of modal gain. The
results of the calculations of the gain spectra for the TE-
mode with due regard to the optical limitation 
 
Γ
 
 factor
for the active region with different numbers of QWs are
shown in Fig. 1. As can be seen in Fig. 1b, a wide QW
amplifies in the long-wavelength region, while a nar-
row (4 nm) QW amplifies in the range 1.35–1.5 
 
µ
 
m. To
obtain a wide and flat gain spectrum, one needs a nar-
row amplifying QW and an absorbing QW. For the TE
mode, a 4-nm-thick QW is amplifying, and a 5 nm-
thick QW is absorbing. A 9-nm-thick QW is used to
increase the total heterostructure gain in the range 1.5–
1.6 
 
µ
 
m. Calculations show that, for an active region
with four QWs, the width of the gain spectrum with an
almost constant maximum value of 
 
~30
 
 cm
 
–1
 
 is
 
~120
 
 nm in the range 1.48–1.6 
 
µ
 
m. As can be seen in
Fig. 1a, the decrease of the number of QWs to three nar-
rows the constant-gain range. An increase in the num-
ber of QWs to five leads to an increase in the maximum
gain; however, the plateau region narrows as well.
The QW thicknesses and excitation levels for the
heterostructures based on narrow-gap GaInAsSb semi-
conductors can be chosen in the same way. The calcu-
lations of the energy levels were performed for the
Ga
 
0.60
 
In
 
0.40
 
As
 
0.36
 
Sb
 
0.64
 
/Al
 
0.35
 
Ga
 
0
 
.65As
 
0.03
 
Sb
 
0.97
 
 system
with the corresponding effective masses in the QWs
(
 
m
 
c
 
 = 
 
0.033
 
m
 
e
 
, 
 
m
 
υ
 
l
 
 = 0.030
 
m
 
e
 
, 
 
m
 
υ
 
h
 
 = 0.289
 
m
 
e
 
) and bar-
rier layers (
 
m
 
c
 
 = 0.075
 
m
 
e
 
, 
 
m
 
υ
 
l
 
 = 0.059
 
m
 
e
 
,
 
m
 
υ
 
h
 
 = 0.295
 
m
 
e
 
).
As can be seen in Fig. 2a, for the QWs with widths
from 5 to 15 nm, the wavelengths of the main optical
transitions lie in the range 2–3 
 
µ
 
m. The optimized
modal gain spectra for the structure with four QWs are
 
g
 
, 
 
cm
 
–1
 
20
0
14
9
4
(a)
(b)
20
0
14
 
9
 
4
5
1300 1400 1500 1600
 
λ
 
, 
 
nm
 
g
 
, 
 
cm
 
–1
 
λ
 
, 
 
µ
 
m
 
λ
 
nm
 
, 
 
µ
 
m
 
3.0
2.5
2.0
1.5
6 8 10 12 14
 
d
 
w
 
, 
 
nm
 
c
 
1
 
–
 
υ
 
h
 
1
 
c
 
1
 
–
 
υ
 
l
 
1
 
c
 
2
 
–
 
υ
 
h
 
2
 
c
 
2
 
–
 
υ
 
l
 
2
 
25
0
2.0 2.4 2.8
10
14
6
4
(a)
(b)
 
Fig. 1.
 
 Gain spectra for the TE mode in a
QW
 
Ga
 
0.45
 
In
 
0.55
 
As/Ga
 
0.17
 
In
 
0.83
 
As
 
0.4
 
P
 
0.6
 
 structure with
(a) three and (b) four QWs at different excitation levels and
QW thicknesses 
 
d
 
w
 
 (numbers at curves in nm) and the total
gain spectrum (thick line); (a) 
 
d
 
 = 4 nm, 
 
∆
 
F
 
 = 0.85 eV, 
 
Γ
 
 =
2.6 
 
·
 
 10
 
–3
 
; 
 
d
 
 = 9 nm, 
 
∆
 
F
 
 = 0.97 eV, 
 
Γ
 
 = 5.9 · 10–3; d = 14 nm,
∆F = 1.0 eV, Γ = 9.1 · 10–3; (b) d = 4 nm, ∆F = 0.98 eV, Γ =
3.2 · 10–3; d = 5 nm, ∆F = 0.80 eV, Γ = 4.0 · 10–3; d = 9 nm,
∆F = 0.93 eV, Γ = 7.2 · 10–3; d = 14 nm, ∆F = 0.93 eV, Γ =
11 · 10–3.
Fig. 2. (a) Wavelengths λnm of the optical transitions in a
QW Ga0.60In0.40As0.36Sb0.64/ Al0.35Ga0.65As0.03Sb0.97
structure between the electron and light-hole levels,
depending on the QW thickness dw and (b) gain spectra for
the TE mode in a QW structure with four QWs at different
excitation levels and QW thicknesses dw (numbers at curves
in nm), and the total gain spectrum (bold line); d = 4 nm,
∆F = 0.50 eV; d = 6 nm, ∆F = 0.52 eV; d = 10 nm, ∆F =
0.68 eV; d = 14 nm, ∆F = 0.59 eV.
BULLETIN OF THE RUSSIAN ACADEMY OF SCIENCES: PHYSICS      Vol. 72      No. 2      2008
LASER DIODES WITH A WIDE FLAT MODAL GAIN SPECTRUM 245
shown in Fig. 2b. According to the calculations, the
width of the range of almost constant gain at a level of
43 cm–1 is ~490 nm.
Thus, the use of asymmetric multilayer QW hetero-
structures based on the GaInPAs and GaInAsSb quater-
nary compounds with inhomogeneously excited active
layers of different thickness allows one to obtain a wide
and almost flat modal gain spectrum in the near-IR
range. The gain spectra of such structures were ana-
lyzed for different excitation levels. At inhomogeneous
excitation of QWs of differing thickness, a wide and
almost flat modal gain spectrum was obtained. It is
shown that the structure with four QWs is optimal for
obtaining a wide and flat modal gain spectrum.
Injection lasers based on AlGaAs, GaInPAs, and
GaInAsSb compounds with a wide flat modal gain
spectrum make it possible to implement two-color
units, if they are connected with a fiber containing two
Bragg gratings, or emitters continuously tuned in a
wide frequency band, when external dispersive ele-
ments are used.
ACKNOWLEDGMENTS
This study was supported by the GKPNI “Photon-
ics” and the Belarussian Republican Foundation for
Basic Research.
REFERENCES
1. Spravochnik po lazeram (Handbook on Lasers),
Prokhorov, A.M., Ed., Moscow: Sovetskoe Radio, 1978.
2. VLOS Volokonno-opticheskie linii svyazi (VLOS Fiber-
Optic Communication Lines), Svechnikov, S.V. and
Andrushenko, L.M., Eds., Kiev: Tekhnika, 1988.
3. Kononenko, V.K., Manak, I.S., and Nalivko, S.V., Spec-
trochim. Acta A, 1999, vol. 55, p. 2091.
4. Manak, I.S., Kononenko, V.K., and Nalivko, S.V., Phys.
Chem. Solid State, 2005, vol. 6, p. 666.
5. Casey, H.C.,Jr. and Panish, M.B., Heterostructure
Lasers, New York: Academic, 1978. Translated under the
title Lazery na geterostrukturakh, Moscow: Mir, 1981.
6. Nalivko, S.V., Manak, I.S., and Chizh, A.L., Litovskii
Fiz. Zh., 1999, vol. 39, no. 1, p. 365.
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Laser Diodes with a Wide Flat Modal Gain Spectrum in the (1–3)- μm Range

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Laser Diodes with a Wide Flat Modal Gain Spectrum in the (1–3)- μm Range

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