Neutral and charged excitons in a CdTe-based quantum well

We present a summary of our spectroscopic studies of the oscillator strength of transitions related to the formation of neutral and positively charged excitons in modulation p-doped CdTe-based quantum wells. The hole concentration was controlled in the range from 10¹⁰ cm⁻² to 10¹¹ cm⁻². Continuous-wave and time-resolved femtosecond pump–probe absorption measurements were performed. They allowed us to study the interacting system of excitons, trions, and free holes. Characteristic times of the system were determined, such as the trion formation time. A new explanation of so-called oscillator strength «stealing» has been proposed, in terms of spin-dependent screening. Experimental evidence is presented for optical creation of transient spin polarization in the quantum well

Oscillating magnetoresistance in diluted magnetic semiconductor barrier structures

Ballistic spin polarized transport through diluted magnetic semiconductor (DMS) single and double barrier structures is investigated theoretically using a two-component model. The tunneling magnetoresistance (TMR) of the system exhibits oscillating behavior when the magnetic field are varied. An interesting beat pattern in the TMR and spin polarization is found for different NMS/DMS double barrier structures which arises from an interplay between the spin-up and spin-down electron channels which are splitted by the s-d exchange interaction.Comment: 4 pages, 6 figures, submitted to Phys. Rev.

INDIRECT EXCHANGE INTERACTION IN Hg1-xMnxTe AND Cd1-xMnxTe ALLOYS

Nous étudions dans les alliages Hg1-xMnxTe et Cd1-xMnxTe l'interaction d'échange indirecte, entre deux moments localisés, qui provient des transitions virtuelles entre la bande de valence remplie et la bande de conduction vide (mécanisme de Bloembergen et Rowland). Nous examinons à la fois le cas de matériaux zérogap (les alliages Hg1-xMnxTe de faible x) et de matériaux semiconducteurs (les alliages Hg1-xMnxTe de grand x et les alliages Cd1-xMnxTe). Nous calculons la température de Curie Weiss et nous la comparons aux résultats expérimentaux existants.We investigate in Hg1-xMnxTe and Cd1-xMnxTe alloys, the indirect exchange interaction between two localized moments, which arises from the virtual transitions between the filled valence band and the empty conduction band (Bloembergen and Rowland mechanism). Both cases of zerogap materials (Hg1-xMnxTe alloys of low x) and semiconducting materials (Hg1-xMnxTe alloys of large x and Cd1-xMnxTe alloys) are examined. The Curie Weiss temperature is calculated and compared to the available experimental results

Scattering Dynamics of Excitons in ZnSe Based Semimagnetic Semiconductors

Resonant Raman scattering was measured for (Zn,Fe)Se and (Zn,Cr)Se with the magnetic ion mole fraction below 0.02. LO phonons and intra-Fe$\text{}^{++}$ transitions were observed. Polarization measurements versus magnetic field allowed to obtain polarization lifetimes (polariton flight times) in the sub-picosecond range

Low temperature specific heat of Fe-based diluted magnetic semiconductors

Specific heat of ZnFeS, ZnFeSe, CdFeSe and HgFeSe is reported for 1.

Low temperature specific heat of Fe-based diluted magnetic semiconductors

Specific heat of ZnFeS, ZnFeSe, CdFeSe and HgFeSe is reported for 1.

Photon Correlations and Cross-Correlations from a Single CdTe/ZnTe Quantum Dot

We report correlation and cross-correlation continuous wave measurements in II-VI quantum dots grown by molecular beam epitaxy. Combination of spectral selection, saturation measurements and good temporal resolution allowed us to see an antibunching effect on photons from radiative recombination of excitons in a single CdTe/ZnTe quantum dot, as well as cross-correlation within the biexciton (X$\text{}_{2}$)-exciton (X) radiative cascade from the same dot. We discuss the results of our experiments in terms of a model of excitonic multitransitions

Influence of configuration mixing on energies and recombination dynamics of excitonic states in CdTe/ZnTe quantum dots

We study experimentally and theoretically excitonic recombination processes in CdTe/ZnTe quantum dots. The single quantum dot photoluminescence spectrum was observed and emission lines from X, X-, X+ and 2X excitonic states were identified. Experimental results were analysed in the theoretical model based on the effective mass approximation. Numerical calculations of energy positions and recombination probabilities of X, X -, X+ and 2X were performed. Computed results reproduce correctly the order and relative positions of emission lines and ratios of radiative lifetimes.Peer reviewed: YesNRC publication: Ye

High-magnetic-field EPR of Cr-based diluted magnetic semiconductors

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