Download The Effect of Magnetic Field on Light/Current and Current/Voltage

International Journal of Pure and Applied Physics.
ISSN 0973-1776 Volume 8, Number 2 (2012), pp. 129-134
© Research India Publications
http://www.ripublication.com/ijpap.htm
The Effect of Magnetic Field on Light/Current and
Current/Voltage Characteristics of MQW Laser
Firas Sabeeh Mohammed
Department of Physics, College of Sciences,
AL–Mustansiriyah University, Iraq
Abstract
The influence of relatively weak magnetic field up to 2 Tesla at room
temperature on light/current and current/voltage characteristics of MQW laser
was examined. Threshold current, forward bias voltage, light output, and
series resistance were studied without and with magnetic field at room
temperature. A fundamental change in laser characteristics was observed by
applying the magnetic field at different directions with respect to the quantum
well plane. The behavior of MQW laser is described in terms of the
temperature-induced changes in the junction voltage and internal series
resistance as well as the current-density alteration when the magnetic field is
applied
Introduction
The application of quantum well structures to semiconductor laser diodes has received
consideration attention because of physical interest as well as its superior
characteristics, such as low threshold current density, low temperature dependence of
threshold current, wavelength tenability, and excellent dynamic properties [1].The
electrical, dynamic and spectral characteristics of laser diode depends on the injection
current, laser temperature and composition. However it is also known to depend on
magnetic field and pressure [2]. Some preliminary, low temperature investigations,
under extremely strong magnetic fields were performed [3]. And to our knowledge,
only a little work related to study the characteristics of quantum well laser (QWL) at
room temperature in relatively weak magnetic field has been reported [4]. The
purpose of this paper is to relate the experimental electrical properties of AlGaInP
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Firas Sabeeh Mohammed
MQWL to existing diode laser models. Light / current, light / voltage, and current /
voltage characteristics recorded without and with magnetic field up to (2 Tesla) at
room temperature. The Landau level based theory was used for explaining the
behavior of laser diode at very low temperature, in strong magnetic field [3]. Our
experimental condition differs from theirs. Therefore we measured these changes in
magnetic field precisely and introduced a shift mechanism in which the carrier
confinement of the laser diode was important. We carried out the experiment by using
high accuracy, stability and high speed digital multimeter, it has 0.01 % DC voltage
basic accuracy, and in order to reduce the error we used digital video camera to
monitor and measure the injection current, output power and bias voltage
instantaneously.
Experimental setup
Figure (1) shows our experimental system and technique used for data acquisition and
analyses and illustrated as follow: the semiconductor laser used in our Experiments is
(Sanyo DL3149-056. AlGalnP Index Guided Multiple Quantum well active laser) and
the lasing wavelength 660 nm at 25°C. The laser diode fixed between poles of a
(7.5mm x 1.3cm x 1.3cm) electromagnetic on L-shape copper block, the copper block
is mounted through Pelter's element (Thermoelectric module TOM-8-127-4-6,0M)
driven by DC current works as a thermal pump. The heat pump is squeezed between
the copper plate and the heat sink, the heat sink was supplied with a fan for an
efficient heat pumping (CPU cooler). Laser mount, photodiode and lens are fixed on
high precise XYZ microposition. For stable operation of laser diode it is necessary
that both injection current and laser temperature are controlled. Current control was
designed and used in order to stabilizer current of the laser diode within (0.05 mA)
and current limit (0-60 mA). The temperature controller was designed both to set the
laser operating temperature and to detect the laser temperature fluctuation and correct
for them. We project the laser beam from laser diode directly at a photodetector
through (colominat lens). We used a Hamamatsou (S2281 Si photodiode). The output
power of laser diode measured by using (DVM) through 1.5 kΩ terminal resistance.
The fluctuation in (power output, laser diode injection current, laser diode
temperature and electromagnet current) are recorded by a digital video camera, and
the time resolution of this measurement is determined by frame of the video camera
system which is ( 1/60 sec). Based on information gained from [5, 6] we found that
the relation between the magnetic field and the laser diode direction is also important.
Therefore, the experiment was performed in the following way. First the magnetic
flux density vector B and the normal direction n of the layered surface of the laser
diode are parallel to each other (B//n) as shown in figure (2a), and second they are
perpendicular (B┴n) as shown in figure (2b).
The Effect of Magnetic Field on Light/Current
131
Figure 1: Experimental Setuup
Figure 2: Orientation of the Magnetic Field
Results and Discussion
Figure (3) and figure (4) shows the light / current characteristics with and without
magnetic field for B//n and B┴n respectively at T=25 ºC. This shows the abrupt onset
of laser action at the threshold current and the increase in the threshold when the
magnetic field is applied for B//n.In the case of B┴n the effect of magnetic field was
small as shown in fig.(4). Fig (5) shows the optical output-power shift versus
magnetic flux density at (T=25 ºC) and (1.05 Ith) injection current condition for B//n
and B┴n. The optical output power decreases when subject to a magnetic field. As the
magnetic field was swept from (0 to 2T), the output power drops from (574.21 to
481.4 µ watt) in the case of B//n and from (574.36 to 535.71µ watt) in the case of
B┴n. Figure (6) shows the voltage / current characteristics at (T=25 ºC), where the
normalized threshold voltage at threshold current and constant light output power
plotted without and with magnetic field for B//n and B┴n. The forward bias voltage
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Firas Sabeeh Mohammed
for AlGaInP MQW laser drops and the series resistance of the laser increases when
the magnetic field applied at the saturation region, no effect has been recorded at
spontaneous and stimulated region. The magnetic field effected currents within and/or
around the active layer and the current flow is altered by the Lorentz force [6]. The
force on the current depends on the relation in direction between a magnetic field and
the current. Thus, the current direction in the active layer is sensitive to the direction
of the magnetic field, Hence the change in the current path causes a change in the
current density in the active layer leading to a change in temperature and carrier
distribution and in turn the oscillation threshold current, forward bias voltage, and
output power shift. In particular, the current I and magnetic field B are parallel (B//I)
for B//n, suppressing the current diffusion leading to a higher current density than
B┴n and a higher temperature, as a result the threshold current takes place toward a
higher side and the series resistance, output power, and forward bias voltage drops
[5].
Figure 3: Light/current characteristics with and without magnetic field at T=25 ºC for
B//n
Figure 4: Light/current characteristics with and without magnetic field at T=25 ºC for
B┴n
The Effect of Magnetic Field on Light/Current
133
Figure 5: The optical output power shift versus magnetic field at T=25ºC and 1.05Ith
injection current condition.
Figure 6: Light/Voltage characteristics without and with magnetic field (2Tesla)
Conclusion
We measured the threshold current, optical output power and forward bias voltage
shifts of MQW laser diode, in a weak magnetic field at room temperature. We
observed the higher threshold current side, the lower power side optical output power
shift and lower forward bias voltage especially for B//n. The behavior of MQW laser
is described in terms of the temperature-induced changes in the junction voltage and
internal series resistance as well as the current-density alteration when the magnetic
field is applied.
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Firas Sabeeh Mohammed
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