2017 11th International Conference on Intelligent Systems and Control (ISCO)
Impact of Length and Thickness of Active Region on Radiated Output Power of
InP/InGaAsP Laser
Ashish Prajapati*, Pritam Dey, Jivesh Verma, T. D. Das
Department of Electronics and Communication Engineering
National Institute of Technology, Arunachal Pradesh, India
*Email: ashishpraj12@gmail.com
Abstract—A double heterostructure light amplification by
stimulated emission of radiation device is designed from two
different semiconductor materials. The material used for the active
region is InGaAsP and is nearly lattice matched with InP acting as
the bulk. We have designed the device in order to observe the
impact of length and thickness of active region on radiated output
power, photon density and the changes in the radiation pattern of
the active region with the variation of length and thickness of the
active region. A proper octagonal coherent monochromatic
radiation pattern is observed as we reduce the thickness but with the
variation of length of the active region, the radiation pattern seems
to get disturbed. For the anode voltage of 1.7V, the maximum light
intensity achieved from the Fabry-Perot laser is 2.72×108 and is
obtained at a wavelength of 1.21µm. In this regard we have studied
the variation of reflectivity as function of length of the active
region.
and is shown in figure1. For designing of the index guided
laser12, InGaAsP/InP14 combination is used because of the
difference in the refractive index of the materials which leads
to the generation of high intense coherent monochromatic15
light source. In this regard, the variation of reflectivity with
length of the simulated device, output power as a function of
current, optimized intensity and anode voltage--anode current
characteristics have been studied. The impact of length and
thickness of active region on the radiation pattern were also
studied.
Index Terms—Double hetero-structure, radiation pattern,
LASER, length, thickness, reflectivity.
I. INTRODUCTION
Semiconductor "light amplification by stimulated emission of
radiation"(LASER)1 have drawn much interest in the field of
electronics as they are compact, efficient, provides direct
modulation and optoelectronic integration etc. In the early
days, 100 mw of power was obtained from small
semiconductor LASERs but with recent developments, 60W
of output power is possible to obtain. For optical
communication, a low noise optical2 fiber amplifier acting as a
pumping source with long span high data rate Fabry-Perot3
edge emitting laser have been simulated with Silvaco-ATLAS
simulation tool. Fabry-Perot LASER oscillates in several
longitudinal modes but with the help of frequency selection,
we have chosen a single mode of oscillation4 at a wavelength
of 1.21µm at which the maximum intensity and high
modulation bandwidth are achieved in the active region. This
wavelength range is thus important for optical fiber
communication5-8. The double heterostructure9 bulk material
without any quantum confinement III-V InGaAsP/InP10
nearly lattice matched semiconductor device is designed in
order to obtain high carrier confinement, lower losses, design
flexibility, reliability11-12 etc. The lower bandgap
semiconductor material is sandwiched between two layers of
higher bandgap material, as a result of which there exists a
potential barrier and the electrons move towards the active
region but still the barrier exists on the side, so the electrons
are forced to remain in the active region and similarly the
holes are confined in the active region and the concentration of
carrier density becomes extremely high for the same current
because the volume where they are confined is very small.
This results in very high Carrier concentration per unit volume
978-1-5090-2717-0/17/$31.00 ©2017 IEEE
Fig.1 Energy band diagram of double heterostructure
InGaAsP/InP laser.
II. DEVICE
PROCEDURE
STRUCTURE
AND
SIMULATION
The schematic of simulated device is shown in figure1.The
energy bandgap of the semiconductor materials InP and
InGaAsP are 10.8 ev and 1.34 ev respectively. The refractive
indices are 3.4 and 3.6 for InP and InGaAsP.
Fig.2 Schematic of double heterostructure bulk Fabry-Perot
LASER.
323
Due to reverse biasing, current blocking layers are generated at
region 2 and 6 which are responsible for higher carrier
confinement in the active region and thus high intensity light
source is designed. The optimum values of different parameters
of the simulated device are mentioned in table1.
Table1: DEVICE DESCRIPTION
Carrier concentration(cm -3)
1
Doping
profile
n-type
2
p-type
2×1017
1.5
3
p-type
2×1017
1.5
4
n-type
18
1×10
0.75
5
p-type
2×1015
0.15
6
n-type
2×1017
1
7
n-type
17
2×10
8
p-type
1×1018
1.6
9
p-type
1×1018
1
p-type
18
10
Thickness(µm)
18
1×10
2×10
0.03
1
1
Total power emitted (W)
Region
During the simulation process, the impact of different
parameters likes length of the active region, thickness of the
active region on generated output power; photon density and
light intensity have been studied. The following results show
the output power variation as a function of anode current,
photon density as function of anode voltage for different
length of the active region.
L=1um
L=2um
L=4um
L=10um
0.02
0.01
0.00
5.5
0.000
The ATLAS model of the simulated device is shown in figure.
The bulk hetero structure is obtained by considering two
semiconductors of different band gap and the radiation pattern
achieved in the active region. These are shown in figure2.
0.001
0.002
0.003
Anode Current (A/m)
III .SIMULATION RESULTS
Fig.5 Variation of output power as function of anode current
L=1um
L=2um
L=4um
L=10um
8
Photon density, mode 1
3x10
8
2x10
8
1x10
0
0.5
1.0
1.5
2.0
Anode Voltage (V)
Fig.6 Variation of photon density as a function of anode
voltage
Fig.3 ATLAS model of Fabry-Perot LASER.
The maximum achieved output power is 24.4 mill watt and is
obtained at a length of 10µm of the active region. In the
process we have studied the variation of light intensity as a
length of the active region and it is seen that as we increase the
length of the active region, the light intensity is reduced and is
shown in figure . In this regard the variation of anode current
as function of anode voltage is also taken into consideration.
The impact of variation of length of the active region in the
designing of the bulk hetero structure laser is given in Table 2.
Table 2: Output obtained for different length of active layers
Length of
active
region(µm)
1
2
4
10
20
Anode
Current(mA)
Output
power(mW)
Photon
density
Light
intensity
2.57
2.45
2.36
2.44
2.15
5.94
9.26
16.2
24.4
24
8.17×107
1.27×108
2.23×108
3.36×108
3.30×108
2.72×108
1.9×108
1.08×108
8.05×107
8.04×107
Fig.4 Radiation pattern and heterostructue generated in the
simulated device.
324
0.003
0.002
Photon density, mode 1 (/cm)
Anode Current (A)
8
L=1um
L=6um
L=12um
L=18um
0.001
0.000
0.5
1.0
1.5
1.2x10
x=100nm
x=50nm
x=25nm
7
6.0x10
0.0
2.0
0.5
1.0
Anode Voltage (V)
1.5
2.0
Anode Voltage (V)
Fig.7 Variation of anode current as a function of anode
voltage
Fig.10 Variation of photon density as a function of anode
voltage
Anode Current (A)
0.004
t=400nm
t=25nm
t=10nm
0.002
0.000
0.5
1.0
1.5
2.0
Anode Voltage (V)
Fig.8 Light intensity as a function of length of the active
region
Fig.11 Variation of anode current as a function of anode
voltage
As we change the thickness of the active region, it is observed
that the light intensity decreases as the thickness of the active
region is reduced, also with thickness, the output power and
the photon density vary. The optimum output power is 9.28
milli watt and is obtained at a thickness of 0.2 µm. At this
particular thickness we obtained the maximum light intensity
which is 1.28×108.The impact of thickness of active region on
the device performance is shown in the following figures.
-2
t=200nm
t=100nm
t=50nm
Total power emitted (W)
1.0x10
Fig.12 The variation of reflectivity as a function thickness
-3
5.0x10
Table: 3 Output obtained for different thickness of active
layers
0.0
0.000
0.001
0.002
0.003
Anode Current (A/m)
Fig.9 Variation of output power as function of input current
Thickness of
active
region(µm)
0.3
0.2
0.1
0.05
0.01
Anode
Current(mA)
Output
power(mW)
Photon
density
Light
intensity
2.32
2.40
2.52
2.67
4
9.24
9.28
9.10
6.63
0.035
1.27×108
1.28×108
1.25×108
9.13×107
4.82×103
2.06×108
2.04×108
1.83×108
1.12×108
5.16×107
325
Reflectivity of the simulated device is related with the length
of the active region by equation (x)
Where αm is the mirror loss and is taken as 21.1 cm-1, L is the
length of the active region,R1 and R2 are reflectivity of the two
cleaved surfaces and the overall value is considered as R. The
variation of R with the length of active region L is tabulated
below and from the observations, it can be concluded that as
the length of the active region increases, the reflectivity so in
the designing process the length of the active region should be
kept minimum.
Table:4 Reflectivity as a function of length of active region
Fig.15 Radiation pattern for varying thickness of active region.
Length of the active region(µm)
Reflectivity (%)
1
2
4
5
99.78
99.57
99.12
98.74
The variation of reflectivity as a function length of the active
region is shown in figure
From the different oscillating modes of Fabry-Perot
LASER, a single mode of oscillation is chosen with the help of
frequency selection method. At a wavelength of 1.21µm which
maximum light intensity and high modulation bandwidth are
achieved in the active region. The light intensity is plotted as a
function of wavelength and is shown in figure
101.0
100.5
100.0
Reflectivity (%)
99.5
99.0
98.5
98.0
97.5
97.0
96.5
96.0
95.5
95.0
-4 -2 0
2
4
6
8 10 12 14 16 18 20 22 24
Length of the active region(µm)
Fig.13 Variation of reflectivity as a function of length of
active region.
As we have varied the thickness of active region, we obtain
more monochromatic coherent radiation pattern which is very
much suitable for the double heterostructure bulk optical
source and on the other hand with the variation of length of the
active region, the shape and pattern of radiation get disturbed.
The radiation pattern of both the cases is shown in figure 14
and 15.
Fig.16 Variation of light intensity as a function of wavelength.
CONCLUSION
We have simulated a high power, efficient 1.21µm double
heterostructure bulk III-V InGaAsP/InP Fabry-Perot edge
emitting laser to achieve monochromatic, coherent light source
from the active region designed with InGaAsP. During the
simulation process we have seen the impact of length and
thickness of the active region on radiated output power,
photon density and anode current. As we reduce the thickness,
a octagonal monochromatic source of radiation is obtained but
it is not so for variation of the length of active region. At a
wave length of 1.21µm, the optimum value of light intensity is
2.72×108.It can also be concluded that the reflectivity
increases as we reduce the length of the active region.
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