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1

Optical Properties of Diluted Magnetic Semiconductor Quantum Structures

100%

Dobrowolska M. , Luo H. , Furdyna J. K.

Acta Physica Polonica A

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1995

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tom 87

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nr 1

95-106

EN

Conduction and valence band edges in diluted magnetic semiconductors undergo enormous Zeeman shifts when a magnetic field is applied, reaching values in excess of 100 meV at low temperatures. These Zeeman shifts can thus have profound consequences on the properties of DMS/non-DMS heterostructures, since they provide the opportunity of tuning their band alignment by varying an applied field. This leads to a variety of entirely new effects, and also provides a powerful tool for probing the effect of band alignment on the properties of semiconductor heterostructures in general. We illustrate this with several examples. First, using the ZnSe/ZnMnSe system, we discuss the creation of a spatial spin modulation (spin superlattice). Second, we use the drastic differences in the Zeeman splitting occurring in different layers of a DMS/non-DMS superlattice in order to pinpoint the localization in space of the specific electronic states involved in optical transitions. We illustrate this by investigating the localization of above-barrier states in type-I ZnSe/ZnMnSe superlattices, and of spatially-direct (type-I) excitons which occur in ZnTe/CdMnSe and ZnMnTe/CdSe type-II super-lattices. Finally, we exploit Zeeman tuning to demonstrate the confinement effects which occur in a single quantum barrier.

2

Persistent Spin Resonance of Donor Electrons and Hopping Magnetoconductivity in Cd_{1-x}Mn_{x}Te_{1-y}Se_{y}

75%

Wojtowicz T. , Semaltianos N. , Kłosowski P. , Dobrowolska M. , Furdyna J. , Miotkowski I.

Acta Physica Polonica A

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1991

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tom 80

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nr 2

287-290

EN

The first observation of electric dipole spin resonance of donor electrons in Cd_{1-x}Mn_{x}Te_{1-y}Se_{y} in far-infrared magnetotransmission is reported. Modification of the donor wave function due to non-diagonal exchange interaction with localized magnetic moments and to magnetic fluctuations are believed to allow this resonance. Hopping magnetoconductivity studied in the same crystals shows a behavior typical for wide gap diluted magnetic semiconductors.

3

Photoluminescence of Donor-Doped ZnSe Films Grown by Molecular Beam Epitaxy

75%

Karczewski G. , Hu B. , Yin A. , Luo H. , Dobrowolska M. , Furdyna J.

Acta Physica Polonica A

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1995

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tom 87

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nr 1

245-248

EN

We studied the effect of the donor doping of ZnSe films on their photoluminescence properties. The samples were doped during the molecular beam epitaxy growth, either with gallium or with chlorine. As the dopant concentration dose increases, the intensity of the band-edge emission first saturates, and then quenches in favor of the deep-level photoluminescence band. The main effect of donor doping on photoluminescence is a strong increase in intensity of the donor-bound exciton line, referred to as I_{2}. For Ga-doped films deep-band emission is much stronger, and the I_{2}-line is slightly weaker than for Cl-doped films with comparable doping level. The results confirm the superiority of chlorine over gallium as an n-type dopant in ZnSe. We discuss the photoluminescence results and relate them to deep level transient spectroscopy data obtained on the same samples.

4

Far-Infrared Magneto-Optical Studies of HgTe-CdTe Superlattices in the Semimetallic Regime

75%

Wojtowicz T. , Dobrowolska M. , Furdyna J. , Meyer J. , Bartoli F. , Hoffman C. , Ram-Mohan L.

Acta Physica Polonica A

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1991

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tom 80

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nr 2

245-254

EN

We review recent magneto-optical investigations performed on HgTe-CdTe semimetallic superlattices. Far infrared magnetotransmission data obtained as a function of temperature, photon energy, and sense of circular polarization are compared with the predictions of a comprehensive new theory which fully incorporates the complexities of type-III superlattice band structure. It is found that the theory accounts for nearly all of the many unusual features which have been observed experimentally. These include the occurrence of two cyclotron resonances due to holes; the coexistence of electron and hole cyclotron resonances in the low temperature limit; the observation of three distinct CRA minima; a step-like change in the temperature dependence of the electron cyclotron mass; and a dramatic increase of the CRI absorption peak intensity with increasing magnetic field.

5

Exchange Coupling in Magnetic Semiconductor Multilayers and Superlattices

75%

Furdyna J. , Leiner J. , Liu X. , Dobrowolska M. , Lee S. , Chung J. , Kirby B.

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EN

The study of ferromagnetic semiconductors continues to be of great interest because of their potential for spintronic devices. While there has been much progress in our understanding of ferromagnetic semiconductor materials - particularly of the canonical III-V system Ga_{1-x}Mn_xAs - many issues still remain unresolved. One of these is the nature of interlayer exchange coupling in GaMnAs-based multilayers, an issue that is important from the point of view of possible spintronic applications. In this connection, it is important to establish under what conditions the interlayer exchange coupling between successive GaMnAs layers is antiferromagnetic or ferromagnetic, since manipulation of such interlayer exchange coupling can then be directly applied to achieve giant magnetoresistance and other devices based on this material. In this review we will describe magneto-transport, magnetization, and neutron reflectometry experiments applied to two types of GaMnAs-based multilayer structures - superlattices and tri-layers - consisting of GaMnAs layers separated by non-magnetic GaAs spacers. These measurements serve to identify conditions under which AFM coupling will occur in such GaMnAs/GaAs multilayer systems, thus providing us the information which can be used for manipulating magnetization (and thus also giant magnetoresistance) in structures based on the ferromagnetic semiconductor GaMnAs.