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Interface Roughness in Quantum Cascade Lasers

Krivas, Kasparas Antanas LU (2015) FYSM60 20141
Mathematical Physics
Abstract
The quantum cascade laser (QCL) is a solid state device capable of generating the coherent mid-infrared and terahertz radiation. It is made from layers of different semiconducting materials. This layered structure gives rise to sub-bands, that are employed to achieve charge inversion necessary for lasing. However, the large number of interfaces that are not perfect strongly influences the operation of the device. In this work we study the influence of interface roughness (IFR) on the performance of the QCL. The program based on non-equilibrium Green's functions were used to simulated two realised terahertz lasers. These simulations provided current density dependence on bias per period and the gain spectrum as well as the energetically and... (More)
The quantum cascade laser (QCL) is a solid state device capable of generating the coherent mid-infrared and terahertz radiation. It is made from layers of different semiconducting materials. This layered structure gives rise to sub-bands, that are employed to achieve charge inversion necessary for lasing. However, the large number of interfaces that are not perfect strongly influences the operation of the device. In this work we study the influence of interface roughness (IFR) on the performance of the QCL. The program based on non-equilibrium Green's functions were used to simulated two realised terahertz lasers. These simulations provided current density dependence on bias per period and the gain spectrum as well as the energetically and spatially resolved charge density.
The obtained data was analysed and compared with reference simulations in order to determine the dominant mechanisms the IFR scattering affects the operation of the QCL.

A number of phenomena were observed. One of them is the additive influence (superposition) of different interfaces on the current density.A shift or a decrease in an emission peak were also observed when interface roughness was altered.

By analysing results, it was determined that interface roughness affects both current and gain of the investigated quantum cascade lasers. It was determined by investigating spatially and energetically resolved electron density, that one of the main mechanisms the IFR affects the operation of the QCL is electron scattering into the lower energy sub-bands in the same well. (Less)
Popular Abstract
Coherent radiation sources (lasers) are devices that have a lot of applications in the modern world. Lasers are used in data storage (optical disc readers), communication infrastructure (fiber-optic Internet), fabrication of various materials and also in spectroscopy. Spectroscopy (the investigation of light after its interaction with matter) can be used to deduce the composition of investigated samples. Since only photons (light particles) of specific energies are absorbed by atoms or molecules, photons of different energies must be used to investigate different materials. Therefore there is a strong reason for developing lasers radiating light at various wavelengths (energies).

Certain ranges of the electromagnetic spectrum are... (More)
Coherent radiation sources (lasers) are devices that have a lot of applications in the modern world. Lasers are used in data storage (optical disc readers), communication infrastructure (fiber-optic Internet), fabrication of various materials and also in spectroscopy. Spectroscopy (the investigation of light after its interaction with matter) can be used to deduce the composition of investigated samples. Since only photons (light particles) of specific energies are absorbed by atoms or molecules, photons of different energies must be used to investigate different materials. Therefore there is a strong reason for developing lasers radiating light at various wavelengths (energies).

Certain ranges of the electromagnetic spectrum are covered by high quality, well developed lasers. However, there exists a gap where laser coverage is poor. The range in question is the mid-infrared and terahertz frequencies. The traditionally used lasers for these wavelengths perform poorly at room temperature (therefore require cooling by liquid nitrogen) or are extremely expensive. In 1994 a new principle for lasing was demonstrated: the quantum cascade laser (QCL). These lasers provided an additional option to cover the mid-infrared and terahertz wavelength range. Two decades after the first realisation of the QCL, the mid-infrared quantum cascade lasers have reached the point where industrial applications are widely used. These lasers can operate at room temperature and are thus suited for everyday use. Terahertz lasers are not there yet, but a lot of effort is being made to improve them.

However, quantum cascade lasers are complicated structures and there are still a lot of gaps in our understanding of these devices. A big effect on the performance of the QCL is due to the interface roughness scattering. The influence of interface roughness is not understood in detail, but there are indications that high interface roughness strongly inhibits the lasing. The aim of this work is to investigate several mechanisms at work in a laser with interface roughness and how they affect the performance of quantum cascade lasers by performing simulations of the structure. (Less)
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author
Krivas, Kasparas Antanas LU
supervisor
organization
course
FYSM60 20141
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Quantum Cascade Lasers, Interface Roughness, Modeling
language
English
id
5043355
date added to LUP
2015-05-19 12:41:49
date last changed
2015-06-02 09:31:44
@misc{5043355,
  abstract     = {The quantum cascade laser (QCL) is a solid state device capable of generating the coherent mid-infrared and terahertz radiation. It is made from layers of different semiconducting materials. This layered structure gives rise to sub-bands, that are employed to achieve charge inversion necessary for lasing. However, the large number of interfaces that are not perfect strongly influences the operation of the device. In this work we study the influence of interface roughness (IFR) on the performance of the QCL. The program based on non-equilibrium Green's functions were used to simulated two realised terahertz lasers. These simulations provided current density dependence on bias per period and the gain spectrum as well as the energetically and spatially resolved charge density. 
The obtained data was analysed and compared with reference simulations in order to determine the dominant mechanisms the IFR scattering affects the operation of the QCL.

A number of phenomena were observed. One of them is the additive influence (superposition) of different interfaces on the current density.A shift or a decrease in an emission peak were also observed when interface roughness was altered.

By analysing results, it was determined that interface roughness affects both current and gain of the investigated quantum cascade lasers. It was determined by investigating spatially and energetically resolved electron density, that one of the main mechanisms the IFR affects the operation of the QCL is electron scattering into the lower energy sub-bands in the same well.},
  author       = {Krivas, Kasparas Antanas},
  keyword      = {Quantum Cascade Lasers,Interface Roughness,Modeling},
  language     = {eng},
  note         = {Student Paper},
  title        = {Interface Roughness in Quantum Cascade Lasers},
  year         = {2015},
}