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1

Tuning of Color Chromaticity of Light Emission from ZnSe Films Grown on a GaAs Substrate by Atomic Layer Epitaxy

100%

Skrobot M., Godlewski M., Guziewicz E., Kopalko K., Phillips M.

Acta Physica Polonica A

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2006

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vol. 110

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issue 3

359-367

EN

Monocrystalline films of sphalerite-type ZnSe were grown on GaAs(100) substrates from elemental Zn and Se precursors by atomic layer epitaxy in a gas flow system. Due to color mixing of band edge and deep defect-related emissions these layers emit intensive white light. Depth profiling cathodoluminescence indicates that green and red emissions mostly come from disordered regions of the films, close to the ZnSe/GaAs interface. We tested a possibility of tuning of chromaticity coordinates and of color temperature of the emission. We found that the chromaticity parameters (color perception) can be tuned by either regulating the appropriate accelerating voltage of electrons or current density of primary electrons in cathodoluminescence investigations. These properties of ZnSe films make them suitable for some practical applications as white light sources.

2

Structure, Surface Morphology and Optical Properties of Thin Films of ZnS and CdS Grown by Atomic Layer Epitaxy

86%

Szczerbakow A., Godlewski M., Dynowska E., Ivanov V., Świątek K., Goldys E., Phillips M.

Acta Physica Polonica A

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1998

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vol. 94

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issue 3

579-582

EN

In this communication we report successful growth of monocrystalline cubic ZnS and monocrystalline and polycrystalline cubic and wurtzite films of CdS by atomic layer epitaxy. Structural and optical properties of these films are analysed. ZnS (and CdS/ZnS) films grown on GaAs substrate are cubic. Atomic layer epitaxy grown films provide several advantages over ZnS and CdS materials grown by other techniques, especially compared to bulk material, which is grown at higher temperatures. First results for ZnS/CdS/ZnS quantum well structures are also discussed.

3

Growth and Characterization of ZnO Nanoparticles

86%

Tomaszewska-Grzęda A., Łojkowski W., Godlewski M., Yatsunenko S., Drozdowicz-Tomsia K., Goldys E., Phillips M.

Acta Physica Polonica A

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2005

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vol. 108

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issue 5

897-902

EN

In this work we evaluate structural and optical properties of ZnO nanoparticles grown by wet chemistry method. Light emission properties of these nanoparticles are studied with cathodoluminescence and micro-photoluminescence. Even at the room temperature excitonic emission is well resolved, due to high exciton binding energy of ZnO. Decay kinetics of photoluminescence emissions and efficiency of inter-nanoparticles energy migration is evaluated from maps of in-plane variations of photoluminescence decay times measured in microphotoluminescence setup.

4

Dynamics of Light Emission in CdMnS Nanoparticles

86%

Godlewski M., Yatsunenko S., Drozdowicz-Tomsia K., Goldys E., Phillips M., Klar P., Heimbrodt W.

Acta Physica Polonica A

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2005

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vol. 108

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issue 4

681-688

EN

We demonstrate coexistence of slow and fast components of photoluminescence decay of the Mn^{2+} intra-shell emission in nanoparticles of CdMnS. We explain the observed decrease in PL lifetime of the Mn^{2+} intra-shell transition by high efficiency of spin dependent magnetic interactions between localized spins of Mn^{2+} ions and free carriers. This mechanism is enhanced in nanostructures, but it is also present in bulk samples.

5

Origin of Ultrafast Component of Photoluminescence Decay in Nanostructures Doped with Transition Metal or Rare-Earth Ions

73%

Godlewski M., Yatsunenko S., Ivanov V., Khachapuridze A., Świątek K., Goldys E., Phillips M., Klar P., Heimbrodt W.

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EN

Bulk samples, layers, quantum well, and quantum dot structures of II-Mn-VI samples all show coexistence of slow and fast components of Mn^{2+} photoluminescence decay. Thus, fast photoluminescence decay cannot be related to low dimensionality of a host material. This also means that the model of the so-called quantum confined atom is incorrect. Based on the results of time-resolved photoluminescence and optically detected magnetic resonance investigations we relate the observed lifetime decrease in Mn^{2+} intra-shell transition to spin dependent magnetic interactions between localized spins of Mn^{2+} ions and between Mn^{2+} ions and spins/magnetic moments of free carriers. The latter mechanism is enhanced in nanostructures.

6

Mechanisms of Yellow and Red Photoluminescence in Wurtzite and Cubic GaN

73%

Godlewski M., Suski T., Grzegory I., Porowski S., Langer R., Barski A., Bergman J., Monemar B., Goldys E., Phillips M.

Acta Physica Polonica A

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1998

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vol. 94

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issue 2

326-330

EN

The origin of two "deep" photoluminescence (PL) emissions observed in wurtzite (yellow PL) and cubic (red PL) GaN is discussed. PL and time-resolved PL studies confirm donor-acceptor pair character of the yellow band in wurtzite GaN and point to participation of shallow donors in this emission. A similar PL mechanism is proposed for the red emission of cubic GaN. We further show a puzzling property of both yellow and red PLs. Both yellow and red emissions show spatial homogeneity and are only weakly dependent on surface morphology.

7

Light Emission Properties of GaN-Based Laser Diode Structures

73%

Godlewski M., Phillips M., Czernecki R., Targowski G., Perlin P., Leszczyński M., Figge S., Hommel D.

Acta Physica Polonica A

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2005

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vol. 108

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issue 4

675-680

EN

Cathodoluminescence is applied for evaluation of in-depth and in-plane variations of light emission from two types of GaN-based laser diode structures. We evaluate in-depth properties of the laser diode emission and demonstrate that potential fluctuations still affect emission of laser diodes for e-beam currents above thresholds for a stimulated emission.

8

Cathodoluminescence Profiling of InGaN-Based Quantum Well Structures and Laser Diodes - In-Plane Instabilities of Light Emission

59%

Godlewski M., Ivanov V., Goldys E., Phillips M., Böttcher T., Figge S., Hommel D., Czernecki R., Prystawko P., Leszczynski M., Perlin P., Grzegory I., Porowski S.

Acta Physica Polonica A

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2003

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vol. 103

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issue 6

689-694

EN

Instabilities of light emission and also of stimulated emission in series of GaN epilayers and InGaN quantum well structures, including laser diode structures, are studied. A stimulated emission is observed under electron beam pumping. This enabled us to study light emission properties from laser structures and their relation to microstructure details. We demonstrate large in-plane fluctuations of light emission and that these fluctuations are also present for excitation densities larger than the threshold densities for the stimulated emission.

9

Relationship between Sample Morphology and Carrier Diffusion Length in GaN Thin Films

59%

Godlewski M., Goldys E., Phillips M., Böttcher T., Figge S., Hommel D., Czernecki R., Prystawko P., Leszczynski M., Perlin P., Wisniewski P., Suski T., Bockowski M., Grzegory I., Porowski S.

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issue 4-5

627-632

EN

Scanning and spot-mode cathodoluminescence investigations of homo- and hetero-epitaxial GaN films indicate a surprisingly small influence of their microstructure on overall intensity of a light emission. This we explain by a correlation between structural quality of these films and diffusion length of free carriers and excitons. Diffusion length increases with improving structural quality of the samples, which, in turn, enhances the rate of nonradiative recombination on structural defects, such as dislocations.

10

Spin Dependent Interactions of Free Carriers and Manganese Ions in Nanostructures of Wide Band Gap II-Mn-VI Semiconductors - Mechanism of Lifetime Reduction

59%

Yatsunenko S., Khachapuridze A., Ivanov V., Godlewski M., Khoi L., Gołacki Z., Karczewski G., Goldys E., Phillips M., Klar P., Heimbrodt W.

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EN

Based on the results of optically detected magnetic resonance and time-resolved investigations we relate the observed lifetime shortening of intra-shell Mn^{2+} emission to spin dependent magnetic interactions between localized spins of Mn^{2+} ions and spins/magnetic moments of free carriers. We show that this mechanism is active in both bulk and in low dimensional structures, such as quantum wells, quantum dots, and nanostructures.

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Tuning of Color Chromaticity of Light Emission from ZnSe Films Grown on a GaAs Substrate by Atomic Layer Epitaxy

Structure, Surface Morphology and Optical Properties of Thin Films of ZnS and CdS Grown by Atomic Layer Epitaxy

Growth and Characterization of ZnO Nanoparticles

Dynamics of Light Emission in CdMnS Nanoparticles

Origin of Ultrafast Component of Photoluminescence Decay in Nanostructures Doped with Transition Metal or Rare-Earth Ions

Mechanisms of Yellow and Red Photoluminescence in Wurtzite and Cubic GaN

Light Emission Properties of GaN-Based Laser Diode Structures

Cathodoluminescence Profiling of InGaN-Based Quantum Well Structures and Laser Diodes - In-Plane Instabilities of Light Emission

Relationship between Sample Morphology and Carrier Diffusion Length in GaN Thin Films

Spin Dependent Interactions of Free Carriers and Manganese Ions in Nanostructures of Wide Band Gap II-Mn-VI Semiconductors - Mechanism of Lifetime Reduction