Wyniki wyszukiwania - Biblioteka Nauki

1

4f Shell of Gd^{2+} and Gd^{3+} Ions in Sn_{1-x}Gd_{x}Te - Resonant Photoemission Study

100%

Kowalski B. J. , Gołacki Z. , Guziewicz E. , Orłowski B. A. , Johnson R. L.

|

nr 5

875-878

EN

Resonant photoemission spectra of Sn_{1-x}Gd_{x}Te (x=0.02 and 0.08) measured for the photon energy range 142 to 151 eV show the valence band density of states distribution and the Gd 4f derived maximum. The energy position of the J=0 component of the Gd 4f maximum was determined and used as a measure of the Gd 4f shell binding energy. The electrostatic model of core level shifts was used to interpret the difference in the Gd 4f binding energies observed for x=0.02 and x=0.08.

2

Optical Properties of ZnCoO Films and Nanopowders

86%

Wolska E. , Łukasiewicz M. , Fidelus J. , Łojkowski W. , Guziewicz E. , Godlewski M.

Acta Physica Polonica A

|

2009

|

tom 116

|

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.

3

Barriers in Miniaturization of Electronic Devices and the Ways to Overcome Them - from a Planar to 3D Device Architecture

86%

Godlewski M. , Guziewicz E. , Gierałtowska S. , Łuka G. , Krajewski T. , Wachnicki Ł. , Kopalko K.

Acta Physica Polonica A

|

2009

|

tom 116

|

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.

4

Visible Luminescence from Porous Silicon

86%

Bała W. , Firszt F. , Nossarzewska-Orłowska E. , Brzozowski A. , Orłowski B. , Kowalski B. , Guziewicz E.

|

nr 4

761-764

EN

This paper presents results of investigation of the temperature dependence of visible luminescence in porous silicon layers prepared by anodization in hydrofluoric acid. Luminescence spectra were measured in the temperature range between 40 K and 350 K. Room temperature reflectivity spectra were also measured in vacuum ultraviolet radiation range from 4 eV to 12 eV.

5

Cathodoluminescence Profiling for Checking Uniformity of ZnO and ZnCoO Thin Films

86%

Witkowski B. , Łukasiewicz M. , Wolska E. , Kopalko K. , Kowalski B. , Guziewicz E. , Godlewski M.

|

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.

6

Response of ZnO/GaN Heterostructure to Ion Irradiation

72%

Barcz A. , Pągowska K. , Kozubal M. , Guziewicz E. , Borysiewicz M. , Dyczewski J. , Jakieła R. , Ratajczak J. , Snigurenko D. , Dynowska E.

|

nr 5

832-835

EN

In this paper we report on the analysis of Al⁺-implanted ZnO/GaN bilayers in search for the damage production mechanism and possible ion mixing. 100 nm or 200 nm thick ZnO epitaxial layers were grown on GaN substrates by either sputter deposition or atomic layer deposition technique followed by adequate annealing. Ion irradiations of ZnO/GaN were carried out at room temperature using 200 keV Al⁺ ions with fluences of 2×10¹⁵ and 10¹⁶ at./cm². Unprocessed and irradiated samples were characterized by the Rutherford backscattering spectrometry in channeling geometry (RBS\c), X-ray diffraction and transmission electron microscopy. Additionally, secondary ion mass spectrometry was employed for the aforementioned samples as well as for the implanted samples subjected to further annealing. It was found that the damage distributions in ZnO/GaN differ considerably from the corresponding defect profiles in the bulk ZnO and GaN crystals, most probably due to an additional strain originating from the lattice mismatch. Amount of intermixing appears to be relatively small; apparently, efficient recombination prevents foreign atoms to relocate to large distances.

7

ZnO by ALD - Advantages of the Material Grown at Low Temperature

72%

Guziewicz E. , Godlewski M. , Krajewski T. , Wachnicki Ł. , Łuka G. , Paszkowicz W. , Domagała J. , Przeździecka E. , Łusakowska E. , Witkowski B.

Acta Physica Polonica A

|

2009

|

tom 116

|

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.

8

Structure Dependent Conductivity of Ultrathin ZnO Films

72%

Snigurenko D. , Kopalko K. , Krajewski T. , Łuka G. , Gierałtowska S. , Witkowski B. , Godlewski M. , Dybko K. , Paszkowicz W. , Guziewicz E.

|

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.

9

Electrostatic Gates for GaN/AlGaN Quantum Point Contacts

72%

Czapkiewicz M. , Cywiński G. , Dybko K. , Siekacz M. , Wolny P. , Gierałtowska S. , Guziewicz E. , Skierbiszewski C. , Wróbel J.

|

nr 6

1026-1028

EN

We report on AlGaN/GaN quantum point contacts fabricated by using e-beam lithography and dry ion etching. The tunable nano-constrictions are defined by the integration of side and top gates in a single device. In this configuration, the planar gates are located on the both sides of a quantum channel and the metallic top gates, which cover the active region, are separated from the substrate by an insulating and passivating layers of HfO_2 or Al_2O_3/HfO_2 composite. The properties of devices have been tested at T = 4.2 K. For side gates we have obtained a very small surface leakage current I_g< 10^{-11} A at gate voltages |V_g| < 2 V, however, it is not enough to close the quantum channel. With top gates we have been able to reach the pinch-off voltage at V_g = - 3.5 V at a cost of I_g ≈ 10^{-6} A, which has been identified as a bulk leakage current.

10

Properties and Characterization of ALD Grown Dielectric Oxides for MIS Structures

72%

Gierałtowska S. , Sztenkiel D. , Guziewicz E. , Godlewski M. , Łuka G. , Witkowski B. , Wachnicki Ł. , Łusakowska E. , Dietl T. , Sawicki M.

|

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.

11

ZnCoO Films by Atomic Layer Deposition - Influence of a Growth Temperature οn Uniformity of Cobalt Distribution

58%

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

|

2009

|

tom 116

|

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.

12

Thin Film ZnO as Sublayer for Electric Contact for Bulk GaN with Low Electron Concentration

58%

Grzanka S. , Łuka G. , Krajewski T. , Guziewicz E. , Jachymek R. , Purgal W. , Wiśniewska R. , Sarzyńska A. , Bering-Staniszewska A. , Godlewski M. , Perlin P.

|

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.

13

Do We Understand Magnetic Properties of ZnMnO?

58%

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.

|

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.