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1
Content available remote Efficient Two-Center Auger Mechanism of Electron Trapping by Fe^{3+} Ions in ZnSe:Fe,Cr
100%
Surma M. , Godlewski M.
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nr 5
1017-1020
EN
A detailed analysis of decay kinetics of light induced electron spin resonance signals of Cr^{1+} and Fe^{3+} ions in ZnSe:Fe,Cr is given. We observe that the Cr^{1+} electron spin resonance signal decays once free electrons are thermally ionized from shallow donors of ZnSe. Such unusual behavior of the Cr^{1+} electron spin resonance signal is explained by efficient two-center Auger recombination: the Cr^{1+} center is ionized due to the Auger-type energy transfer from the electron being trapped by the Fe^{3+} ion. Such process is shown to be consistent with the temperature dependence of the decay times of electron spin resonance signals. Its quantum efficiency is estimated to be as large as 18% for Cr and Fe concentrations which were studied.
2
Content available Spin Relaxation Processes in Quantum Well Structures of Cd_{1-x}Mn_xTe/Cd_{1-x}Mg_xTe
80%
Khachapuridze A. , Ivanov V. , Godlewski M. , Karczewski G.
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nr 4-5
643-648
EN
Fast spin relaxation of Mn^{2+} ions in a magnetic quantum well of CdMnTe with 1% Mn fraction is related to a very efficient spin-flip interaction between Mn ions and free carriers. This mechanism of spin relaxation becomes dominant at increased excitation densities. The observed response of the photoluminescence bands to the Mn^{2+} magnetic resonance indicates that free carriers are heated at the magnetic resonance conditions. A decrease in formation/recombination rates of free and trion excitons is observed. Donor bound exciton photoluminescence is enhanced, which we relate to delocalization of free excitons, caused by interaction with microwave heated free carriers.
3
Content available remote Transition Metal Impurities and Electronic Structure of ZnSe-Based Isovalent Semiconductor Alloys
80%
Surkova T. P. , Giriat W. , Godlewski M. , Permogorov S.
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nr 5
1009-1012
EN
Energy level positions of the nickel 2+/1+ and cobalt 2+/3+ charge states have been used to estimate band edges for the valence and conduction bands of ZnSe-based alloys with cation (ZnCdSe) and anion (ZnSSe) substitution. Chemical trends in band offsets of heterostructures of Zn- or Mn-based II-VI compounds are analysed. Further on, the change of Ni^{2+}(3d^{8}) and Co^{2+}(3d^{7}) intra-d shell transition bands upon the alloying of host material is discussed.
4
Content available remote Hot Carrier Effects in Optically Detected Cyclotron Resonance Studies of III-V Semiconductors
80%
Karpińska K. , Dedulewicz S. , Godlewski M.
Acta Physica Polonica A
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1992
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tom 82
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nr 4
623-626
EN
The mechanisms of irregular photoluminescence intensity oscillations, as observed in optically detected cyclotron resonance experiments, are discussed. Two possible scenarios are analyzed, both requiring impact ionization of the center(s) by electric field accelerated free carriers. The first assumes coexistence of dielectric and energy relaxation processes. The second assumes a subsequent impact ionization of two different centers.
5
Content available remote Infrared Absorption Study of Thermally Generated Shallow Donor Centers in Czochralski Silicon
80%
Kaczor P. , Kopalko K. , Godlewski M. , Gregorkiewicz T.
Acta Physica Polonica A
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1992
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tom 82
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nr 4
677-680
EN
A comparative study of thermally generated donor centers in boron and aluminum doped Czochralski silicon was performed by means of Fourier transform infrared technique. A detailed study revealed presence of donor centers belonging to the well-known series of thermal donors and shallow thermal donors. For both types of material the same centers could be observed while considerable differences in their generation kinetics occurred. In addition to the previously identified species also new ones could be observed. One of them, with single ionization level at approximately 39.5 meV, was found to exhibit clear dependence of its concentration upon illumination of the sample during cooling from room temperature to liquid He temperature.
6
Content available remote ZnO Nanopowders by a Microwave Hydrothermal Method - Influence of the Precursor Type on Grain Sizes
80%
Wolska E. , Witkowski B. , Godlewski M.
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nr 5
683-685
EN
Two series of ZnO nanopowders obtained by a microwave hydrothermal method are examined. We used two different zinc precursors (zinc chloride (ZnCl_2) and zinc nitrate hexahydrate (N_2O_6Zn·6H_2O)). Both types of nanopowders show a bright emission in a visible light, including the band edge emission, which indicates their good crystallographic quality. Results of scanning electron microscopy, photo- and cathodoluminescence investigations are presented.
7
Content available remote AlGaAs to GaAs Energy Transfer Mechanisms in AlGaAs/GaAs Structures
71%
Karpińska K. , Godlewski M. , Żytkiewicz Z. , Chen W. , Weber E.
Acta Physica Polonica A
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1992
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tom 82
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nr 4
713-716
EN
The results of photoluminescence and optically detected cyclotron resonance experiments are presented for thick AlGaAs epilayers grown by liquid phase electroepitaxy method on GaAs:Cr substrate. These results indicate an efficient energy transfer from excited AlGaAs to GaAs.
8
Content available remote Photo-ESR Study of the DX to Shallow Donor Conversion in Te Doped Al_{x}Ga_{1-x}As
71%
Surma M. , Żytkiewicz Z. , Fronc K. , Stalinga P. , Godlewski M.
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nr 4
757-760
EN
Results of detailed electron spin resonance (ESR) study of Te doped Al_{x}Ga_{1-x}As epilayers with x = 0.41, 0.42, and 0.5 Al fractions are presented. It is shown that the ESR signal observed critically depends on cooling steps and that the shallow donor ESR signal can be observed prior to illumination. The first ESR study of AlGaAs layers with removed GaAs substrate are presented. The mechanism of the enhanced photosensitivity of the ESR signal is explained. It is found very paradoxical that the ESR signals decreases upon the illumination even though shallow donor concentration is increased.
9
Content available remote Optical Properties of ZnCoO Films and Nanopowders
61%
Wolska E. , Łukasiewicz M. , Fidelus J. , Łojkowski W. , Guziewicz E. , Godlewski M.
Acta Physica Polonica A
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2009
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tom 116
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nr 5
918-920
EN
ZnCoO is one of the most studied and promising semiconductor materials for spintronics applications. In this work we discuss optical and electrical properties of ZnCoO films and nanoparticles grown at low temperature by either atomic layer deposition or by a microwave driven hydrothermal method. We report that doping with cobalt quenches a visible photoluminescence of ZnO. We could observe a visible photoluminescence of ZnO only for samples with very low Co fractions (up to 1%). Mechanisms of photoluminescence quenching in ZnCoO are discussed. We also found that ZnO films remained n-type conductive after doping with Co, indicating that a high electron concentration and cobalt 2+ charge state can coexist.
10
Content available remote Barriers in Miniaturization of Electronic Devices and the Ways to Overcome Them - from a Planar to 3D Device Architecture
61%
Godlewski M. , Guziewicz E. , Gierałtowska S. , Łuka G. , Krajewski T. , Wachnicki Ł. , Kopalko K.
Acta Physica Polonica A
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2009
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tom 116
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nr S
S-19-S-21
EN
We witness a new revolution in electronic industry - a new generation of integrated circuits uses as a gate isolator HfO_{2}. This high-k oxide was deposited by the atomic layer deposition technique. The atomic layer deposition, due to a high conformality of deposited films and low growth temperature, has a large potential to be widely used not only for the deposition of high-k oxides, but also of materials used in solar cells and semiconductor/organic material hybrid structures. This opens possibilities of construction of novel memory devices with 3D architecture, photovoltaic panels of the third generation and stable in time organic light emitting diodes as discussed in this work.
11
Content available remote Mechanism of Optical Detection of Magnetic Resonance in Cd_{1-x}Mn_{x}Te
61%
Godlewski M. , Surma M. , Gałązka R. , Nguyen K. , Gisbergen S. , Gregorkiewicz T. , Ammerlaan C.
Acta Physica Polonica A
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1992
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tom 82
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nr 4
717-719
EN
The photoluminescence and optically detected magnetic resonance studies of Cd_{1-x}Mn_{x}Te (x = 0.095) are presented. The Mn^{2+} magnetic resonance is detected optically via the changes of "edge" emission induced by the decrease of the Mn spin system magnetization.
12
Content available remote Cathodoluminescence Profiling for Checking Uniformity of ZnO and ZnCoO Thin Films
61%
Witkowski B. , Łukasiewicz M. , Wolska E. , Kopalko K. , Kowalski B. , Guziewicz E. , Godlewski M.
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nr 5
675-677
EN
We employ scanning electron microscopy and cathodoluminescence for evaluation of uniformity of ZnCoO films obtained by the atomic layer deposition. Cathodoluminescence quenching by Co ions allows us to detect (regions of weaker light emission) Co accumulations, with the resolution limited by diffusion length of secondary carriers.
13
Content available Origin of Ultrafast Component of Photoluminescence Decay in Nanostructures Doped with Transition Metal or Rare-Earth Ions
51%
Godlewski M. , Yatsunenko S. , Ivanov V. , Khachapuridze A. , Świątek K. , Goldys E. , Phillips M. , Klar P. , Heimbrodt W.
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nr 1
65-74
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.
14
Content available remote ZnO by ALD - Advantages of the Material Grown at Low Temperature
51%
Guziewicz E. , Godlewski M. , Krajewski T. , Wachnicki Ł. , Łuka G. , Paszkowicz W. , Domagała J. , Przeździecka E. , Łusakowska E. , Witkowski B.
Acta Physica Polonica A
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2009
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tom 116
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nr 5
814-817
EN
The 3D-architecture is a prospective way in miniaturization of electronic devices. However, this approach can be realized only if metal paths are placed not only at the top, but also beneath the electronic parts, which imposes drastic temperature limitations for the electronic device processing. Therefore last years a lot of investigations are focused on materials which can be grown at low temperature with electrical parameters appropriate for electronic applications. Zinc oxide grown by the atomic layer deposition method is one of the materials of choice. We obtained ZnO-ALD films at growth temperature range between 100°C and 200°C, and with controllable electrical parameters. Free carrier concentration was found to scale with deposition temperature, so it is possible to grow ZnO films with desired conductivity without any intentional doping. We used correlation of electrical and optical parameters to optimize the deposition process. Zinc oxide layers obtained in that way have free carrier concentration as low as 10^{16} cm^{-3} and high mobility (10-50 cm^{2}/(Vs)), which satisfies requirements for a material used in three-dimensional memories.
15
Content available remote Structure Dependent Conductivity of Ultrathin ZnO Films
51%
Snigurenko D. , Kopalko K. , Krajewski T. , Łuka G. , Gierałtowska S. , Witkowski B. , Godlewski M. , Dybko K. , Paszkowicz W. , Guziewicz E.
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nr 6
1042-1044
EN
Zinc oxide films dedicated for hybrid organic/inorganic devices have been studied. The films were grown at low temperature (100°C, 130C and 200°C) required for deposition on thermally unstable organic substrates. ZnO layers were obtained in atomic layer deposition processes with very short purging times in order to shift a structure of the films from polycrystalline towards amorphous one. The correlation between atomic layer deposition growth parameters, a structural quality and electrical properties of ZnO films was determined.
16
Content available remote Properties and Characterization of ALD Grown Dielectric Oxides for MIS Structures
51%
Gierałtowska S. , Sztenkiel D. , Guziewicz E. , Godlewski M. , Łuka G. , Witkowski B. , Wachnicki Ł. , Łusakowska E. , Dietl T. , Sawicki M.
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nr 5
692-695
EN
We report on an extensive structural and electrical characterization of undergate dielectric oxide insulators Al_2O_3 and HfO_2 grown by atomic layer deposition. We elaborate the atomic layer deposition growth window for these oxides, finding that the 40-100 nm thick layers of both oxides exhibit fine surface flatness and required amorphous structure. These layers constitute a base for further metallic gate evaporation to complete the metal-insulator-semiconductor structure. Our best devices survive energizing up to ≈ 3 MV/cm at 77 K with the leakage current staying below the state-of-the-art level of 1 nA. At these conditions the displaced charge corresponds to a change of the sheet carrier density of 3 × 10^{13} cm^{-2}, which promises an effective modulation of the micromagnetic properties in diluted ferromagnetic semiconductors.
17
Content available Relationship between Sample Morphology and Carrier Diffusion Length in GaN Thin Films
41%
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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nr 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.
18
Content available remote ZnCoO Films by Atomic Layer Deposition - Influence of a Growth Temperature οn Uniformity of Cobalt Distribution
41%
Łukasiewicz M. , Witkowski B. , Godlewski M. , Guziewicz E. , Sawicki M. , Paszkowicz W. , Łusakowska E. , Jakieła R. , Krajewski T. , Kowalik I. , Kowalski B.
Acta Physica Polonica A
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2009
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tom 116
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nr 5
921-923
EN
We report on the structural, electrical and magnetic properties of ZnCoO thin films grown by atomic layer deposition method using reactive organic precursors of zinc and cobalt. As a zinc precursor we applied either dimethylzinc or diethylzinc and cobalt(II) acetyloacetonate as a cobalt precursor. The use of these precursors allowed us the significant reduction of a growth temperature to 300°C and below, which proved to be very important for the growth of uniform films of ZnCoO. Structural, electrical and magnetic properties of the obtained ZnCoO layers will be discussed based on the results of secondary ion mass spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, atomic force microscopy, Hall effect and SQUID investigations.
19
Content available remote Thin Film ZnO as Sublayer for Electric Contact for Bulk GaN with Low Electron Concentration
41%
Grzanka S. , Łuka G. , Krajewski T. , Guziewicz E. , Jachymek R. , Purgal W. , Wiśniewska R. , Sarzyńska A. , Bering-Staniszewska A. , Godlewski M. , Perlin P.
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nr 5
672-674
EN
Fabrication of low resistivity ohmic contacts to N polarity gallium nitride crystal is an important issue for the construction of the vertical current flow devices like laser diodes and high brightness light emitting diodes. Gallium nitride is a challenging material because of the high metal work function required to form a barrier-free metal-semiconductor interface. In practice, all useful ohmic contacts to GaN are based on the tunneling effect. Efficient tunneling requires high doping of the material. The most challenging task is to fabricate high quality metal ohmic contacts on the substrate because the doping control is here much more difficult that in the case of epitaxial layers. In the present work we propose a method for fabricating low resistivity ohmic contacts on N-side of GaN wafers grown by hydride vapor phase epitaxy. These crystals were characterized by a n-type conductivity and the electron concentration of the order of 10^{17} cm^{-3}. The standard Ti/Au contact turned out to be unsatisfactory with respect to its linearity and resistance. Instead we decided to deposit high-n type ZnO layers (thickness 50 nm and 100 nm) prepared by atomic layer deposition at temperature of 200°C. The layers were highly n-type conductive with the electron concentration in the order of 10^{20} cm^{-3}. Afterwards, the metal contact to ZnO was formed by depositing Ti and Au. The electrical characterization of such a contact showed very good linearity and as low resistance as 1.6 × 10^{-3} Ω cm^2. The results indicate advantageous properties of contacts formed by the combination of the atomic layer deposition and hydride vapor phase epitaxy technology.
20
Content available remote Do We Understand Magnetic Properties of ZnMnO?
41%
Godlewski M. , Wójcik A. , Kopalko K. , Ivanov V. , Wilamowski Z. , Jakieła R. , Guziewicz E. , Szczepanik A. , Dłużewski P. , Chikoidze E. , Barjon J. , Dumont Y. , Putkonen M. , Niinistö L. , Tang D.
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nr 2
261-267
EN
Optical and magnetic properties of ZnMnO films are discussed based on the results of cathodoluminescence, photoluminescence, and magneto-photoluminescence investigations. We show that photoluminescence/cathodoluminescence emissions are strongly quenched and become in-plane inhomogeneous in samples with increased Mn fractions. Strong polarization of photoluminescence is observed, even though excitonic lines do not shift and are not split at magnetic fields up to 6 T.
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