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1

Femtosecond Dynamics of Neutral and Charged Exciton Absorption in Cd_{1-x}Mn_xTe Quantum Well

100%

Płochocka P., Kossacki P., Maślana W., Radzewicz C., Gaj J., Cibert J., Tatarenko S.

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issue 4-5

679-686

EN

We present a study of time-dependent transmission spectra of a modulation-doped Cd_{1-x}Mn_xTe/Cd_{1-y-z}Zn_yMg_zTe quantum well with variable hole gas concentration. We study the influence of pump pulses on excitonic absorption in subpicosecond time scale. A spectrally broad probe pulse of duration of 40 femtoseconds was used to record the absorption spectra at controlled delay. Studies of temporal evolution of exciton energies revealed coherence decay of linearly polarized excitons and thermalization of non-equilibrium exciton states. We found that a characteristic timescale for thermalization of non-equilibrium populations of photocreated excitons is between 0.8 and 3.6 ps. The timescale of this process depends on the hole concentration in quantum well: for higher hole concentration the decay is faster. Long-lived photo-induced magnetization accompanied by heating of the magnetic system was also observed.

2

Oscillator Strengths for Neutral, Charged, and Scattered Excitons in CdTe Quantum Wells Containing a 2D Electron Gas

100%

Cox R., Huard V., Bourgognon C., Saminadayar K., Tatarenko S., Miller R.

Acta Physica Polonica A

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2004

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vol. 106

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issue 3

287-298

EN

Absorption spectra have been measured for a 10 nm CdTe(0.3%Mn) quantum well with electron concentration n_e variable up to 1.5×10^{11}cm^{-2}. Following recent theory appropriate to low n_e, here ≈0.1/π a_B^2, the spectra are interpreted in a "strong exciton" model, where the initial oscillator strength of the excitonic resonance (X) is conserved, with screening and phase-space filling effects negligible. As n_e increases in zero-field and as the filling factorν increases in magnetic field, the intensity of X is transferred to: (i) trion processes, namely exciton-one electron scattering and the trion resonance (T), and (ii) quatron processes, namely exciton-two electron scattering and trion-one electron scattering. In magnetic field, the three- and four-body scattering processes become discrete, combined "exciton and cyclotron" and combined "trion and cyclotron" excitations that take all the intensity of X and T for ν≾1 and ν>2, respectively.

3

Ferromagnetism in II-VI Based Semiconductor Structures

100%

Cibert J., Ferrand D., Tatarenko S., Wasiela A., Kossacki P., Dietl T.

Acta Physica Polonica A

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2001

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vol. 100

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issue 2

227-236

EN

The experimental results on carrier-induced ferromagnetic interaction in II-VI diluted magnetic semiconductors are shortly reviewed and analyzed in the light of the mean field approximation. We particularly take the point of view of the experimentalist to emphasize (i) points which are easily understood within this simple model (as the role of the detailed structure of the valence band) and hence should be incorporated into more sophisticated models, and (ii) points which are not taken into account in the mean field model (e.g., disorder effects) and hence call for more elaborate descriptions. We particularly discuss the case of a low carrier density, and show that the situation appears as experimentally very different in the highly disordered 3D layers and in the modulation doped 2D quantum wells.

4

Carrier Density Control by Illumination in Surface Doped, p-Type (Cd,Mn)Te Quantum Wells

84%

Maślana W., Kossacki P., Gaj J., Ferrand D., Bertolini M., Tatarenko S., Cibert J., Kutrowski M., Wojtowicz T.

Acta Physica Polonica A

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2006

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vol. 110

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issue 2

255-262

EN

We report both decrease and increase in the 2D carrier gas density in a simple (Cd,Mn)Te/(Cd,Mg)Te heterostructure with (Cd,Mn)Te quantum well. The two effects were achieved by light with different photon energies. The quantum wells were 10 nm wide with 2D hole gas supplied by surface states. For the sample with 25 nm cap layer thickness, it was possible to tune the hole gas concentration from almost empty well (hole density below 1×10^{10} cm^{-2}) to 45×10^{10} cm^{-2}. The illumination with 425 nm wavelength almost doubled the hole gas density from the initial 24×10^{10} cm^{-2}. The depletion mechanism was most effective for illumination with the orange (575 nm) light.

5

Control of Ferromagnetism in Cd_{1-x}Mn_xTe Based Quantum Wells

84%

Bertolini M., Boukari H., Ferrand D., Cibert J., Tatarenko S., Gilles B., Maślana W., Gaj J., Kossacki P., Dietl T.

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issue 4-5

603-608

EN

New structures aiming at controlling the ferromagnetic properties of diluted magnetic semiconductor quantum wells are presented. The carrier density is controlled by applying a voltage across a p-i-n diode. A new method, creating a 2D hole gas by adjusting the distance between the quantum well and surface, offers opportunities for a broader range of structures.

6

Photoluminescence of p-Doped Quantum Wells with Strong Spin Splitting

84%

Boukari H., Kossacki P., Bertolini M., Ferrand D., Cibert J., Tatarenko S., Gaj J., Deveaud B., Ciulin V.

Acta Physica Polonica A

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2004

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vol. 106

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issue 3

299-310

EN

Photoluminescence of p-type modulation doped (Cd,Mn)Te quantum wells is studied with carrier density up to 5×10^{11} cm^{-2} at various spin splittings. This splitting can be made larger than the characteristic energies of the system thanks to the giant Zeeman effect. At small spin splitting and regardless of the carrier density, the photoluminescence exhibits a single line, which corresponds to the charged exciton in the singlet state. Above a certain spin splitting, the charged exciton is destabilized in favor of the exciton at vanishing hole density, and in favor of a double line at higher carrier density. It is found here that the charged exciton destabilization energy hardly depends on the carrier density. The double line is found to be band-to-band like, with the same initial state - where the holes have the same spin orientation - and final states that differ by some excitation of the 2D hole gas. In addition, the spin splitting needed to fully polarize the hole gas is twice smaller than expected from the single particle image and gives a unique insight into many-body effects in the hole gas.

7

Exciton Trions in II-VI Heterostructures

84%

Cox R., Huard V., Kheng K., Lovisa S., Miller R., Saminadayar K., Arnoult A., Cibert J., Tatarenko S., Potemski M.

Acta Physica Polonica A

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1998

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vol. 94

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issue 2

99-109

EN

Optical spectra associated with transitions that create or annihilate charged excitons X^{-} or X^{+} can be observed in quantum well heterostructures containing an electron gas or a hole gas, respectively. A review is given of properties of trion states in CdTe quantum wells in zero field and of the magnetic field-dependence of the circular polarization and oscillator strength of the trion optical resonance. The possibility that disorder is needed to stabilise trion states in concentrated 2D electron or hole systems is discussed.

8

Many-Body Interactions in the CdTe-Based Quantum Well under Strong Optical Excitation

84%

Płochocka P., Kossacki P., Piechal B., Maślana W., Golnik A., Cibert J., Tatarenko S., Gaj J.

Acta Physica Polonica A

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2004

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vol. 106

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issue 3

413-422

EN

We performed pump-probe time-resolved absorption measurements on a modulation p-doped (Cd,Mn)Te quantum well. The density of the 2D hole gas was controlled, in the 10^{10} cm^{-2} range, by additional cw illumination. Interactions between photocreated neutral (X) and charged (X^{+}) excitons and the 2D hole gas were analyzed. We found that the strongest effect is the influence of the carriers on both X and X^+ optical resonances. Neutral and charged excitons are screened by holes, which results in the decrease in their intensities. We conclude from polarization resolved experiments that this screening is spin-dependent: it is more efficient between holes with opposite spins. Binding holes into the charged excitons reduces the screening of the neutral excitons and leads to an enhancement of the neutral exciton intensity. We also analyzed weaker effects, due to exciton-exciton interaction, at a constant hole density. We found that the reduction of the neutral exciton intensity due to two different mechanisms (phase-space filling and biexciton formation) is almost equal. We observed a spin-dependent blue shift of the neutral exciton line in the presence of a population of neutral excitons created by the pump pulse. Due to the attractive interaction between excitons with opposite spins, the corresponding shift of the neutral exciton is smaller than that observed due to the interaction between excitons with the same spins.

Refine search results

Femtosecond Dynamics of Neutral and Charged Exciton Absorption in Cd_{1-x}Mn_xTe Quantum Well

Oscillator Strengths for Neutral, Charged, and Scattered Excitons in CdTe Quantum Wells Containing a 2D Electron Gas

Ferromagnetism in II-VI Based Semiconductor Structures

Carrier Density Control by Illumination in Surface Doped, p-Type (Cd,Mn)Te Quantum Wells

Control of Ferromagnetism in Cd_{1-x}Mn_xTe Based Quantum Wells

Photoluminescence of p-Doped Quantum Wells with Strong Spin Splitting

Exciton Trions in II-VI Heterostructures

Many-Body Interactions in the CdTe-Based Quantum Well under Strong Optical Excitation