[Show abstract][Hide abstract] ABSTRACT: Further development and commercialization of the new generation of optoelectronic and photovoltaic is often limited by the necessity of fabrication of low-cost and efficient transparent conductive electrodes. The development so far is hindered by the conveniently used indium tin oxide (ITO), which suffers from high cost and not high enough availability to support mass production. The zinc oxide is emerging as a convenient replacement for ITO for solar cell and light-emitting diode applications. The optical functions of aluminum-doped zinc oxide thin films are determined using optical spectroscopy measurements from 300 to 1100 nm. The dopant range studied varies from intrinsic ZnO to 5% Al content. Below the direct band gap there is a residual enhancement of the optical absorption coefficient by Al dopants, which is not related to surface roughness. We determined the dielectric functions and absorption coefficient evolution as the dopant concentration increases, as well as the free-carrier concentration.
29th European Photovoltaic Solar Energy Conference and Exhibition, Amsterdam; 11/2014
[Show abstract][Hide abstract] ABSTRACT: This paper we discusses an effect of coating long-period gratings (LPGs) with a thin titanium dioxide (TiO 2) overlays on refractive index (RI) sensitivity of the LPG. The overlays have been obtained using atomic layer deposition (ALD) method. The method allows for deposition well-controlled in thickness, well defined in optical properties, high-RI and very conformal thin films as required for optical fiber sensors. For the investigated LPGs we obtained sensitivity of 3490 to 6471 nm per RI unit depending on range RI. Keywords-Atomic Layer Deposition (ALD); thin films; long-period gratings (LPGs); titanium dioxide (TiO 2); optical fiber sensors; refractive index sensing
International Journal on Smart Sensing and Intelligent Systems. 09/2014; 7(3):573.
[Show abstract][Hide abstract] ABSTRACT: The Symposium F: “Novel materials for electronic, optoelectronic, photovoltaic and energy saving applications” of the 2013 E-MRS Fall Meeting (held in Warsaw, Poland, on 16–20 September 2013) was organized to cover many important aspects of basic and applied research of novel materials for present and future industrial applications. Particular emphasis was given to new technological and application concepts concerning both bulk crystals and various quantum structures of reduced dimensionality, like quantum wells and quantum dots (nanoparticles). The presented results on application-oriented materials were mostly focused on light emitting structures, light detectors, solar cells and materials for spintronics. Special attention was given to the technological aspects and challenges: growth techniques, defect control and structure optimization, doping procedures, optical properties and degradation processes. Relevant experimental techniques and crystal growth procedures were also discussed. Experimental results were compared with theoretical calculations giving deeper insight into many problems of modern materials science. Over 100 researchers from all over the world participated in this symposium, giving in all 15 invited lectures, 38 contributed talks and 70 poster presentations.
[Show abstract][Hide abstract] ABSTRACT: Oxide nanoparticles doped with rare-earth ions are tested for applications as nanomarkers in biology and medicine, e.g. for early cancer diagnostics. In this work we describe properties of such markers obtained by a microwave hydrothermal technology. Nanomarkers based on oxide materials (ZnO) are grown and tested for medical and biological applications.
[Show abstract][Hide abstract] ABSTRACT: Aluminum-doped zinc oxide (AZO) films were grown on polyethylene terephthalate (PET) substrates by atomic layer deposition (ALD) at low deposition temperatures (110–140 °C). The films have low resistivities, ∼10−3 Ω cm, and high transparency (∼90%) in the visible range. Bending tests indicated a critical bending radius of ≈1.2 cm, below which the resistivity changes became irreversible. The films deposited on PET with additional buffer layer are more stable upon bending and temperature changes.
Materials Science and Engineering B 08/2014; · 1.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on the properties of photovoltaic (PV) structures based on thin films of n-type zinc oxide grown by atomic layer deposition method on a cheap silicon substrate. Thin films of ZnO are used as n-type partner to p-type Si (110) and, when doped with Al, as a transparent electrode. PV structures with different thicknesses of ZnO layers (from 600 nm to 1600 nm) were deposited to determine the optimal performance of PV structures. The best response we obtained for the structure with ZnO layer thickness of 800 nm. The so-obtained PV structures show 6% efficiency.
Thin Solid Films 07/2014; 563:28–31. · 1.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work is focused on the electrical and optical analyses used to estimate the activation energy of the dominant shallow donor in thin ZnO films obtained at low temperature by the atomic layer deposition process. These two approaches, based on the temperature-dependent classical Hall effect and photoluminescence investigations, yielded a donor activation energy ED in the range of 30–40 meV, including the estimated error margins. This value, as confirmed by layer composition studies, is attributed to the presence of zinc atoms in the interstitial positions of the ZnO lattice.
[Show abstract][Hide abstract] ABSTRACT: 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 (PL) of ZnO. We
could observe a visible PL of ZnO only for samples with very low Co fractions
(up to 1%). Mechanisms of PL 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.
[Show abstract][Hide abstract] ABSTRACT: Selected properties of photovoltaic (PV) structures based on n-type zinc oxide nanorods grown by a low temperature hydrothermal method on p-type silicon substrates (100) are investigated. PV structures were covered with thin films of Al doped ZnO grown by atomic layer deposition acting as transparent electrodes. The investigated PV structures differ in terms of the shapes and densities of their nanorods. The best response is observed for the structure containing closely-spaced nanorods, which show light conversion efficiency of 3.6%.
Beilstein Journal of Nanotechnology 01/2014; 5:173-9. · 2.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aluminum-doped zinc magnesium oxide (Zn1−x
O:Al) films with the Mg content from x = 0 to 0.48 were obtained using atomic layer deposition (ALD). Together with the thorough studies of the properties of the deposited films, the ALD growth parameters conditioning possible applications of Zn1−x
O:Al films as transparent electrodes are investigated. Very low film resistivities (≤~10−3 Ω cm) and the metallic-type conductivity behavior at room temperature for Zn1−x
O:Al films are observed for Mg content x < 0.19. The Mg content of x = 0.19 results in the optical absorption edge of Zn1−x
O:Al films at 3.81 eV (325 nm). Other film parameters like work function or sheet resistance can be easily modified by variation of growth parameters.
Journal of Materials Science 01/2014; 49:1512-1518. · 2.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The paper presents photoemission studies of wide band gap semiconductors
surfaces doped with gadolinium and samarium. The contribution of the
Gd4f and Sm4f electrons to the electronic structure of the doped
semiconductor systems (CdTe, GaN and ZnO) was evaluated based on the
Fano resonance measured across the RE4d → RE4f intra-ion
photoionization threshold. It was found that the RE valence and position
of the RE4f shell varies significantly between the investigated
semiconductor systems and depends not only on the used semiconductor
matrix but also on the Fermi level position.
[Show abstract][Hide abstract] ABSTRACT: Optical and magneto-optical properties of ZnCoO films grown at low
temperature by Atomic Layer Deposition are discussed. Strong wide band
absorption, with onset at about 2.4 eV, is observed in ZnCoO in addition to
Co-related intra-shell transitions. This absorption band is related to Co 2+ to
3+ photo-ionization transition. A strong photoluminescence (PL) quenching is
observed, which we relate to Co recharging in ZnO lattice. Mechanisms of PL
quenching are discussed.
[Show abstract][Hide abstract] ABSTRACT: A simple fabrication method of silver (Ag) nanoislands on ZnO films is presented. Continuous wave and time-resolved photoluminescence and transmission are employed to investigate modifications of visible and UV emissions of ZnO brought about by coupling to localized surface plasmons residing on Ag nanoislands. The size of the nanoislands, determining their absorption and scattering efficiencies, is found to be an important factor governing plasmonic modification of optical response of ZnO films. The presence of the Ag nanoislands of appropriate dimensions causes a strong (threefold) increase in emission intensity and up to 1.5 times faster recombination. The experimental results are successfully described by model calculations within the Mie theory.
[Show abstract][Hide abstract] ABSTRACT: Oxide-based thin-film capacitors (TFCs), thin-film transistors (TFTs), and sensor structures (including transparent ones) deposited on transparent substrates are investigated. All oxide elements in these structures are deposited by atomic layer deposition (ALD). Optimization of the ALD processes, which results in layers suitable for the above-mentioned devices, is briefly described. In particular, we demonstrate advantageous properties of composite dielectrics consisting of pairs of Al2O3, HfO2, ZrO2, or TiO2. These composites are then used as gate dielectrics in TFC and TFT structures, with ZnO layers deposited as channel and gate layers. The structures are obtained at low temperatures (no more than 150°C), which enables their deposition on elastic, transparent substrates (polymers, foils).
Chemical Vapor Deposition 06/2013; 19(4‐6). · 1.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, a n-ZnO/p-GaN heterojunction is analyzed using admittance spectroscopy techniques. Capacitance transient measurements performed at 10 kHz reveal four majority-carrier deep levels, the most important one located at approximately 0.57 eV below the ZnO conduction band (CB) edge with a density about two orders of magnitude below the doping level (NT = 4 × 1015 cm−3). The others, located at 0.20 eV, 0.65 eV, and 0.73 eV, are about three orders of magnitude below the doping level (NT = 4–9 × 1014 cm−3).
Journal of Applied Physics 05/2013; 113(19). · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work presents an application of thin zinc oxide (ZnO) films
obtained using atomic layer deposition (ALD) for effective tuning of
spectral response and the refractive-index (RI) sensitivity of
long-period gratings (LPGs). The technique allows for an efficient and
well controlled deposition at monolayer level of excellent quality
nano-films as required for optical sensors. The effect of ZnO deposition
on spectral properties of the LPGs is discussed. We correlated the
increase in ZnO thickness with the shift of the LPG resonance wavelength
and proved that similar films are deposited on fibers and silicon
reference samples in the same process run. The thin overlay effectively
changes the distribution of the cladding modes and thus also tunes the
device's RI sensitivity. The tuning can be simply realized by varying
number of cycles, which is proportional to thickness of the
high-refractive-index (n<1.9 in infrared spectral range) ZnO film.
The advantage of this approach is precision in determining the film
thickness resulting in RI sensitivity of the LPGs.
[Show abstract][Hide abstract] ABSTRACT: Luminescent properties of ZnO nanorods covered with Ag nanoparticles are examined. Nanorods were synthesized on AAO templates using Atomic Layer Deposition (ALD) technique. Two types of the samples were prepared with different arrangement of ZnO nanorods and doping conditions. Nanorods of the second type were codoped with Al, to stimulate defect-related emissions. The ZnO material fills heterogeneously the interior of the AAO nanopores and has hexagonal, wurtzite structure. Both types of structures exhibit a broad defect-related emission at about 440 nm, most probably related to recombination at zinc interstitial (Zni) defects. This emission in samples with a random distribution of ZnO:Al nanorods and finer Ag nanoparticles is enhanced by factor of ∼2.5 upon Ag deposition. The so-obtained material is interesting from the point of view of its application in blue range emitting diodes.
Applied Physics A 04/2013; 111:265-271. · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We demonstrate the fabrication and properties of an near ultraviolet organic light emitting diode (UV OLED) that contains 2,7-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole organic emitting layer and aluminum-doped magnesium zinc oxide (ZnMgO:Al) layer as transparent electrode. The obtained ZnMgO:Al layer is transparent for the wavelengths longer than 325 nm and has low resistivity of the order of 10-3 Ωcm. The UV OLED device turns on at the applied voltage of 9 V.
[Show abstract][Hide abstract] ABSTRACT: A series of (Zn,Co)O layers with Co contents x up to 40% grown by atomic layer deposition have been investigated. All structures deposited at 160 ∘C show magnetic properties specific to II-VI dilute magnetic semiconductors with localized spins S=3/2 coupled by strong but short-range antiferromagnetic interactions resulting in low-temperature spin-glass freezing for x=0.16 and 0.4. At higher growth temperature (200∘C) metallic Co nanocrystals precipitate in two locations giving rise to two different magnetic responses: (i) a superparamagnetic contribution coming from volume disperse nanocrystals; (ii) a ferromagneticlike behavior brought about by nanocrystals residing at the (Zn,Co)O/substrate interface. It is shown that the dipolar coupling within the interfacial two-dimensional dense dispersion of nanocrystals is responsible for the ferromagneticlike behavior.
Physical Review B 01/2013; 88:085204. · 3.66 Impact Factor