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On Optical Characterization of Carrier Lifetimes in GaN Layers by Time-Resolved Four-Wave Mixing and Photoluminescence Techniques

100%
Malinauskas T., Jarašiūnas K.
Acta Physica Polonica A
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2005
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vol. 108
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issue 5
781-787
EN
We provide numerical analysis of nonequilibrium carrier dynamics in GaN layers at interband photoexcitation by a picosecond light pulse. By solving the continuity equation for bipolar carrier plasma, we analyze spatial and temporal evolution of carrier density. We show that fast carrier diffusion to the bulk determines the carrier in-depth profile in GaN epilayers with a thickness larger than the carrier diffusion length. By integrating the carrier spatial profiles at experimental conditions, corresponding to time-resolved four-wave mixing and time-resolved photoluminescense we simulate the four-wave mixing and time-resolved photoluminescense kinetics in subnanosecond time domain. The modeling data using parameters of the studied GaN epilayers (their thickness, diffusion coefficient, carrier lifetime, and absorption coefficients at emission wavelengths) were compared with the experimental results. The analysis provided conditions at which the discrepancy between the measured carrier lifetime by time-resolved photoluminescense and time-resolved four-wave mixing may occur. For hydride-vapor phase epitaxy GaN layers with a large diffusion length, the fast photoluminescense kinetics are confirmed by modeling and experiments that they are due to diffusion governed carrier in-depth redistribution, while four-wave mixing kinetics remain insensitive for carrier in-depth redistribution.
2
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On Oscillating Carrier Dynamics in Highly Excited InP:Fe Crystals

81%
Subačius L., Kadys A., Jarašiūnas K., Kamiński P.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
855-858
EN
The numerical analysis and experimental data on time-resolved four-wave mixing confirmed a novel origin of oscillations in subnanosecond carrier dynamics in highly excited InP:Fe crystals. The effect was attributed to simultaneous presence of electron and hole gratings, which drift in the space charge field and contribute constructively or destructively to refractive index modulation in time domain.
3
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Time-Resolved Transient Grating Spectroscopy for Studies of Nonequilibrium Carrier Dynamics in Wide Band-Gap Semiconductors

71%
Jarašiūnas K., Malinauskas T., Neimontas K., Gudelis V., Aleksiejūnas R.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
201-209
EN
Using interdisciplinary fields relevant to a highly excited semiconductor - nonequilibrium phenomena in high density plasma, light-induced changes of optical properties, and dynamic holography, we developed time-resolved four-wave mixing technique for monitoring the spatial and temporal carrier dynamics in wide band-gap semiconductors. This opened a new possibility to analyse fast electronic processes in a non-destructive "all-optical" way, i.e. without any electrical contacts. This technique allowed evaluation of recombination and transport processes and the determination of important carrier parameters which directly reveal the material quality: carrier lifetime, bipolar diffusion coefficients, surface recombination rate, nonlinear recombination rate, diffusion length, threshold of stimulated recombination. The recent experimental studies of differently grown group III-nitrides (heterostructures and free standing films) as well silicon carbide epilayers by nondegenerate picosecond four-wave mixing are presented.
4
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High-Speed Quadratic Electrooptic Nonlinearity in dc-Biased InP

71%
Subačius L., Kašalynas I., Vingelis M., Aleksiejūnas R., Jarašiūnas K.
Acta Physica Polonica A
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2005
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vol. 107
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issue 2
280-285
EN
We present experimental data on degenerate four-wave mixing as well as simulation results of fast optical nonlinearities in highly-excited semi-insulating InP under applied dc-field. Hot-electron transport governed enhancement of optical nonlinearity is obtained by applying a dc-field of 10-14 kV/cm at full-modulation depth of a light-interference pattern. The hydrodynamic model, which incorporates both free-carrier and photorefractive nonlinearities is used to explain the experimentally observed features. We show that the enhancement of optical nonlinearity is due to the quadratic electrooptic effect.
5
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Transients of Carrier Recombination and Diffusion in Highly Excited GaN Studied by Photoluminescence and Four-Wave Mixing Techniques

52%
Juršėnas S., Miasojedovas S., Kurilčik G., Žukauskas A., Aleksiejūnas R., Malinauskas T., Sūdžius M., Jarašiūnas K.
Acta Physica Polonica A
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2005
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vol. 107
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issue 2
240-244
EN
Time-resolved photoluminescence and four-wave mixing techniques have been combined for studies of carrier relaxation dynamics in a highly photoexcited GaN epilayer. For a moderate excitation density below 1 mJ/cm^2, carrier recombination was due to free carrier capture by deep traps. The characteristic time of carrier capture,τ_e=550 ps, was measured under deep trap saturation regime. The ambipolar diffusion coefficient for free carriers, D=1.7 cm^2/s, was estimated from the analysis of the transients of the light-induced gratings of various periods. A complete saturation of the four-wave mixing efficiency was observed for the excitation energy density exceeding 1.5 mJ/cm^2. The latter saturation effect was shown to be related to electron-hole plasma degeneration, which results in a significant enhancement of carrier recombination rate due to onset of stimulated emission.
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