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4 Acta Physica Polonica A

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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.

Acta Physica Polonica A

2002

tom 102

nr 4-5

679-686

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.

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.

Acta Physica Polonica A

2002

tom 102

nr 4-5

603-608

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.

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

2006

tom 110

nr 2

255-262

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.

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

2004

tom 106

nr 3

413-422

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.