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1
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Intervalley Scattering and the Role of Indirect Band Gap AlAs Barriers: Application to GaAs/AlGaAs Quantum Cascade Lasers

100%
Mc Tavish J., Ikonić Z., Indjin D., Harrison P.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
891-902
EN
We report on the results of our simulations of Γ-X scattering in GaAs/AlGaAs heterostructures, discussing the importance of the mole fraction, doping density, and lattice and electron temperature in determining the scattering rates. We consider three systems, a single quantum well (for the investigation of Γ-X scattering), a double quantum well (to compare the Γ-X-G and Γ-Γ scattering rates), and an example of a GaAs/AlGaAs mid-infrared quantum cascade laser. Our simulations suggest that Γ-X scattering can be significant at room temperature but falls off rapidly at lower temperatures. One important factor determining the scattering rate is found to be the energy difference between the Γ- and X-states.
2
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Quantum Dots as Sources and Detectors οf Mid- and Far-Infrared Radiation: Theoretical Models

100%
Vukmirović N., Indjin D., Ikonić Z., Harrison P.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
464-467
EN
We present a review of theoretical methods used to study the electronic structure, optical and transport properties of intraband optoelectronic devices based on self-assembled quantum dots.
3
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Charge Carrier Transport in Quantum Cascade Lasers in Strong Magnetic Field

88%
Radovanović J., Milanović V., Indjin D., Ikonić Z., Harrison P.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
99-102
EN
We have developed a comprehensive rate equations based model for calculating the optical gain in the active region of a quantum cascade laser in magnetic field perpendicular to the structure layers, which takes into account all the relevant scattering channels. The model is applied to gain-optimized quantum cascade laser active region, obtained by a systematic optimization procedure based on the use of genetic algorithm, which we have previously set up for designing novel structures and improving performance of existing ones. It has proven to be very efficient in generating optimal structures which emit radiation at specified wavelengths corresponding to absorption fingerprints of particular harmful pollutants found in the atmosphere. We also illustrate another interesting prospective application of quantum cascade laser-type structures: the design of metamaterials with tunable complex permittivity, based on amplification via intersubband transitions. In this case, the role of the magnetic field is to assist the attainment of sufficient optical gain (population inversion), necessary to effectively manipulate the permittivity and fulfill the conditions for negative refraction (left-handedness).
4
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Quantum Cascade Laser Design for Tunable Output at Characteristic Wavelengths in the Mid-Infrared Spectral Range

88%
Daničić A., Radovanović J., Milanović V., Indjin D., Ikonić Z.
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issue 5
772-776
EN
We present a method for systematic optimization of quantum cascade laser active region, based on the use of the genetic algorithm. The method aims at obtaining a gain-maximized structure, designed to emit radiation at specified wavelengths suitable for direct absorption by pollutant gasses present in the ambient air. After the initial optimization stage, we introduce a strong external magnetic field to tune the laser output properties and to slightly modify the emission wavelength to match the absorption lines of additional compounds. The magnetic field is applied perpendicularly to the epitaxial layers, thus causing two-dimensional continuous energy subbands to split into series of discrete Landau levels. This affects all the relevant relaxation processes in the structure and consequently the lifetime of carriers in the upper laser level. Furthermore, strong effects of band nonparabolicity result in subtle changes of the lasing wavelength at magnetic fields which maximize the gain, thus providing a path for fine-tuning of the output radiation properties. Numerical results are presented for GaAs/Al_{x}Ga_{1-x}As based quantum cascade laser structures designed to emit at particular wavelengths in the mid-infrared part of the spectrum.
5
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Time Delay in Thin Slabs with Kerr-Type Nonlinearity

88%
Radovanović J., Milanović V., Isić G., Ikonić Z., Indjin D.
Acta Physica Polonica A
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2007
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vol. 112
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issue 5
987-992
EN
In this paper we analyzed the following model: a thin slab with Kerr nonlinearity placed between two semi-infinite samples of linear and nonmagnetic materials. A general relation between the bidirectional group delay and the dwell time is derived for the thin slab. It is shown that the group delay is equal to the dwell time plus a self-interference delay. Particular attention is given to solving the Helmholtz equation for this case. Detailed and rigorous treatment revealed that the solutions of the Helmholtz equation are given via elliptic functions of the first kind. The boundary conditions at the interfaces are determined precisely. Finally, we provide an overall procedure for numerical calculation of the dwell times.
6
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Spin Precession of Quasi-Bound States in Heterostructures with Spin-Orbit Interaction

76%
Isić G., Indjin D., Ikonić Z., Milanović V., Radovanović J., Harrison P.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
513-515
EN
We use a finite-difference model that is capable of describing the single state spin dynamics in a double-barrier AlGaAs heterostructure. The use of Green's functions enables a description of the double-barrier structure by a finite matrix while the interaction with contacts is described by appropriate self-energies. To account for interface roughness scattering, a self-energy Σp_{IR}(E, k) is derived within the random phase approximation. The dominant part is due to in-plane momentum relaxation while a smaller part describing spin-flip scattering is neglected. The former only decreases the state lifetime while the latter can also affect the spin precession frequency.
7
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Content available

Carrier Dynamics in Quantum Cascade Lasers

64%
Harrison P., Indjin D., Jovanović V., Mirčetić A., Ikonić Z., Kelsall R., McTavish J., Savić I., Vukmirović N., Milanović V.
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EN
A fully quantum-mechanical model for carrier scattering transport in semiconductor intersubband devices was applied to modelling of carrier dynamics in quantum cascade lasers. The standard model uses the envelope function and effective mass approximations to solve electron band structure under an applied bias. The k·p model has been employed in p-type systems where the more complex band structure requires it. The resulting wave functions are then used to evaluate all relevant carrier-phonon, carrier-carrier and alloy scattering rates from each quantised state to all others within the same and the neighbouring period. This piece of information is then used to construct a rate equation for the equilibrium carrier density in each subband and this set of coupled rate equations are solved self-consistently to obtain the carrier density in each eigenstate. The latter is a fundamental description of the device and can be used to calculate the current density and gain as a function of the applied bias and temperature, which in turn yields the threshold current and expected temperature dependence of the device characteristics. A recent extension which includes a further iteration of an energy balance equation also yields the electron (or hole) temperature over the subbands. This paper will review the method and describe its application to mid-infrared and terahertz, GaAs, GaN, and SiGe cascade laser designs.
8
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Normal Incidence Mid-Infrared Photocurrent in AlGaN/GaN Quantum Well Infrared Photodetectors

52%
Sherliker B., Halsall M., Harrison P., Jovanović V., Indjin D., Ikonić Z., Parbrook P., Whitehead M., Wang T., Buckle P., Phillips J., Carder D.
Acta Physica Polonica A
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2005
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vol. 107
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issue 1
174-178
EN
We report the growth and characterization of AlGaN/GaN multiple quantum well structures designed to have intersubband transitions in the mid-infrared region of the spectrum. The samples were nominally undoped but were found to contain a high electron population in the wells induced by the local polarization fields. The sample was characterized by the use of the Raman spectroscopy and photocurrent spectroscopy. The Raman spectroscopy shows electronic Raman scattering from intersubband transitions in the AlGaN/GaN quantum wells. The e_1-e_2 and e_1-e_3 transitions of the confined 2d electron population in the wells can clearly be observed. A sample designed to absorb at 4μm was fabricated into mesa structures and the vertical photocurrent measured under normal incidence illumination from the free-electron laser FELIX. A wavelength and bias dependent photocurrent was observed in the mid-IR region of spectrum. The peak responsivity was of the order of 50μA/W at 4 K, the photocurrent still being measurable at room temperature.
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