Doping Layers in Quantum Cascade Lasers: A study in doping density, position and migration effects
(2022) FYSM60 20151Mathematical Physics
- Abstract
- Quantum Cascade Lasers (QCLs) consist of several semiconductor materi-
als sandwiched together. The QCL achieves stimulated emission in the mid-IR
(m-IR) to the THz region of the electromagnetic spectrum by inter-subband
transitions. These parts of the electromagnetic spectrum are hard to lase in
with conventional means. This makes them highly eligible in spectroscopic
applications used in many research areas including chemistry, physics and
medicine. These structures are also important because instead of a large laser which requires much equipment to lase in the wanted region, only a small chip can be used. The QCLs which lase in the IR operate at room temperature, but the operating temperature of the THz QCLs is low which... (More) - Quantum Cascade Lasers (QCLs) consist of several semiconductor materi-
als sandwiched together. The QCL achieves stimulated emission in the mid-IR
(m-IR) to the THz region of the electromagnetic spectrum by inter-subband
transitions. These parts of the electromagnetic spectrum are hard to lase in
with conventional means. This makes them highly eligible in spectroscopic
applications used in many research areas including chemistry, physics and
medicine. These structures are also important because instead of a large laser which requires much equipment to lase in the wanted region, only a small chip can be used. The QCLs which lase in the IR operate at room temperature, but the operating temperature of the THz QCLs is low which constitutes a problem. This limits their applicability. It is therefore beneficial to have a THz system which operates at room temperature. Hence continued research about these systems (in the THz) is important.
In this thesis work, three studies have been performed. The first study
investigated the impact of changing the doping density. The second study
considered the impact of changing the position of the doping layer. The third
study investigated if dopant migration effects can account for experimental
results on symmetric QCLs. This thesis work is theoretical and the results
are simulated using a FORTRAN programme which is based on Non Equilib-
rium Green's Function Theory (NEGFT). The results of the studies will be
compared to experimental measurements when this is possible.
In this investigation it has been shown that the current densities and the
gain are highly dependent on the doping density and the position of the doping layer. Dopant migration effects have also been investigated and it has been found that the case when the diffusion of the charge carriers have spread out over almost the entire period gives the closest correspondence to the reference results. (Less) - Popular Abstract
- Quantum Cascade Lasers (QCLs) are semiconductor devices which in contrast to other semiconductor lasers which utilise transitions across the band gap, are based on inter subband transitions. Hence radiation in the mid-IR and THz range of the electromagnetic spectrum is received. QCLs are important because they can be used in many research areas such as chemistry, physics and medicine. The THz QCLs however have a limited operating temperature due to the properties of their structure. Therefore it is important to research and develop better structures which can operate at higher temperatures. The position and density of the doping layers are two important attributes which have been investigated in this thesis work.
The work has been... (More) - Quantum Cascade Lasers (QCLs) are semiconductor devices which in contrast to other semiconductor lasers which utilise transitions across the band gap, are based on inter subband transitions. Hence radiation in the mid-IR and THz range of the electromagnetic spectrum is received. QCLs are important because they can be used in many research areas such as chemistry, physics and medicine. The THz QCLs however have a limited operating temperature due to the properties of their structure. Therefore it is important to research and develop better structures which can operate at higher temperatures. The position and density of the doping layers are two important attributes which have been investigated in this thesis work.
The work has been theoretical in character and addresses three different issues i) the impact of the doping density, ii) the position of the doping layer, iii) adding migration effects (due to diffusion of the added impurities when the laser is grown). The results were simulated in a computer program using Non-Equilibrium Green’s Function Theory.
During this investigation it has been found that when changing the doping density the photon energy and gain change accordingly. Hence the same periodic structure will have a different laser output by just increasing or decreasing the doping density. This is in response to increased scattering and a shift in the potential due to bending of the conduction band edge. This investigation has also shown that the laser output is highly dependent on where the doping layer is placed. So when constructing the QCL, the position of the doping layer and the doping density have to be taken into account carefully in order to receive the desired frequency. Dopant migration has been simulated and it is probable that this accounts for the bias polarity dependence reported in experimental results on symmetric QCLs; even though the migration must be large in order to affect the theoretical results. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9071332
- author
- Reftlér, Josefin
- supervisor
- organization
- course
- FYSM60 20151
- year
- 2022
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9071332
- date added to LUP
- 2022-01-12 11:18:25
- date last changed
- 2022-01-12 11:18:25
@misc{9071332,
abstract = {{Quantum Cascade Lasers (QCLs) consist of several semiconductor materi-
als sandwiched together. The QCL achieves stimulated emission in the mid-IR
(m-IR) to the THz region of the electromagnetic spectrum by inter-subband
transitions. These parts of the electromagnetic spectrum are hard to lase in
with conventional means. This makes them highly eligible in spectroscopic
applications used in many research areas including chemistry, physics and
medicine. These structures are also important because instead of a large laser which requires much equipment to lase in the wanted region, only a small chip can be used. The QCLs which lase in the IR operate at room temperature, but the operating temperature of the THz QCLs is low which constitutes a problem. This limits their applicability. It is therefore beneficial to have a THz system which operates at room temperature. Hence continued research about these systems (in the THz) is important.
In this thesis work, three studies have been performed. The first study
investigated the impact of changing the doping density. The second study
considered the impact of changing the position of the doping layer. The third
study investigated if dopant migration effects can account for experimental
results on symmetric QCLs. This thesis work is theoretical and the results
are simulated using a FORTRAN programme which is based on Non Equilib-
rium Green's Function Theory (NEGFT). The results of the studies will be
compared to experimental measurements when this is possible.
In this investigation it has been shown that the current densities and the
gain are highly dependent on the doping density and the position of the doping layer. Dopant migration effects have also been investigated and it has been found that the case when the diffusion of the charge carriers have spread out over almost the entire period gives the closest correspondence to the reference results.}},
author = {{Reftlér, Josefin}},
language = {{eng}},
note = {{Student Paper}},
title = {{Doping Layers in Quantum Cascade Lasers: A study in doping density, position and migration effects}},
year = {{2022}},
}