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 degrees 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 degrees 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.

For more than a decade ZnO doped with Mn and Co has remained as one of the most prospected diluted magnetic semiconductor for spintronic applications with conflicting outcome concerning the genuineness of its room temperature ferromagnetism. In order to clarify this issue we investigate (Zn,Co)O layers grown by atomic layer deposition at low temperatures. We employ and relay on wide range of extensive material characterization, which in combination with superconducting quantum interference device magnetometry allow us decisively exemplify the growth temperature as the key factor discriminating between paramagnetic (obtained at 160 °C) and various forms of ferromagnetic responses, seen when the grows is carried out at 200 °C and above.

This work reports on the Schottky junctions based on zinc oxide layers (grown by Atomic Layer Deposition from dimethylzinc (Zn(CH3)2) or diethylzinc (Zn(C2H5)2) and water precursors). If the strict electrical requirements (electron concentration not higher than 10 cm and mobility above 10 cmVs) for ZnO are fulfilled, the rectification ratio of ZnO/Ag Schottky junction as high as 10 for low forward bias (2 – 3 V) can be achieved. The ideality factor of about η ≈ 2.65 was calculated basing on the pure thermionic emission theory.

Despite many efforts, the origin of a ferromagnetic (FM) response in ZnMnO and ZnCoO is still not clear. Magnetic investigations of our samples, not discussed here, show that the room temperature FM response is observed only in alloys with a non-uniform Mn or Co distribution. Thus, the control of their distribution is crucial for the explanation of contradicted magnetic properties of ZnCoO and ZnMnO reported till now. In this paper, we discuss advantages of the atomic layer deposition (ALD) growth method, which enables us to control the uniformity of ZnMnO and ZnCoO alloys. Properties of ZnO, ZnMnO and ZnCoO films grown by the ALD are discussed.

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.

ZnO based diluted magnetic semiconductors are intensively investigated for possible spintronic applications. In the present work we investigate the ZnCoO layers grown at low temperature by atomic layer deposition. The local atomic structure of a series of layers with different Co concentration is investigated by the X-ray absorption fine structure measurements. Two groups of ZnCoO layers are investigated - the ones with an uniform Co distribution and highly nonuniform films. For uniform samples we observe that a majority of Co atoms is built into the ZnO matrix substituting the Zn atoms. In contrast, for the nonuniform samples, metallic Co inclusions are also observed. These results are in strong correlation with the magnetic properties of the films studied separately. Samples with the uniform Co distribution (Co substitutes Zn in ZnO) are paramagnetic, whereas the nonuniform ones show a ferromagnetic response.

This work reports on the zinc oxide layers grown by atomic layer deposition (ALD) from dimethylzinc (Zn(CH3)(2), DMZn) or diethylzinc (Zn(C2H5)(2), DEZn) and deionized water precursors. These films are suitable for nanoelectronic applications, e.g. selecting elements in the new generation of non-volatile 3D memories constructed in the cross-bar architecture. This architecture imposes strict requirements on the parameters of obtained ZnO layers. Growth temperature must be below 200 degrees C, electron concentration not higher than 10(17) cm(-3) and mobility above 10 cm(2) V-1 s(-1). This is possible when the ALD growth method is used. We demonstrate the correlations between the structural, optical and electrical properties of ALD-ZnO layers. Their control allows us to obtain Schottky junctions with silver, whose parameters are suitable for the applications mentioned above. The ideality factor of about eta approximate to 2.65 was calculated for the Schottky diodes based on the pure thermionic emission theory.

We demonstrate that room temperature ferromagnetic response (RT FR) of ZnCoO films grown at low temperature by the atomic layer deposition (ALD) method is due to Co metal accumulations at the ZnCoO/substrate interface region. The accumulated experimental evidences allow us to reject several other explanations of this effect in our samples, despite the fact that some of them are likely to be responsible for the low temperature FM in this class of the material.

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.

The electronic structure of ferromagnetic (Zn,Co)O films was investigated by resonant photoemission across the Co 3p -> Co 3d photoionization threshold, e.g. using photon energy between 50 eV and 66 eV. The films were grown by atomic layer deposition at temperature between 160 degrees C and 300 degrees C and they differed in distribution and content of cobalt. The maximum of the Fano resonance was observed at photon energy 63 eV, whereas the minimum at 58 eV. The difference between energy distribution curves taken at 63 eV and the one taken at 58 eV was calculated for a series of samples. It shows that the Co 3d contribution to the valence band electronic structure of ferromagnetic (Zn,Co)O films differs significantly from that of the films which show the paramagnetic response.

ZnCuO thin lms have been deposited on silicon, glass and quartz substrates by atomic layer deposition method, using reactive organic precursors of zinc and copper. As zinc and copper precursors we applied diethylzinc and copper(II) acetyloacetonate. Structural, electrical and optical properties of the obtained ZnCuO layers are discussed based on the results of scanning electron microscopy, energy dispersive spectroscopy, X-ray di raction, atomic force microscopy, the Hall e ect and photoluminescence investigations.

Electrical and magnetic properties of ZnCoO thin films grown on silicon substrates by atomic layer deposition method are investigated. The films were grown using reactive organic precursors of zinc and cobalt. The use of these precursors allowed us the significant reduction of a growth temperature to 200 C and below, which proved to be very important for the growth of uniform films of ZnCoO. We have measured the microwave AC conductivity and EPR for two types of ZnCoO samples, with different Co fractions.

We show that the atomic layer deposition (ALD) technique has great potential for widespread use in the production of ZnO films for applications in electronic, photovoltaic (PV), and optoelectronic devices. The low growth temperature makes ALD-grown ZnO films suitable for fabrication of various semiconductor/organic hybrid structures. This opens up the possibility of novel devices based on very cheap organic materials, including organic light emitting diodes and third-generation PV cells.

We present results of a resonant photoemission study of (Zn,Co)O films with Co content between 2% and 7%. The films were grown by Atomic Layer Deposition (ALD) at low temperature of 160°C, and show fully paramagnetic behavior. The Co ions are uniformly distributed in the ZnO matrix and are free of foreign phases and metal accumulations as indicated by TEM data. The electronic structure of (Zn,Co)O films was studied by Resonant Photoemission Spectroscopy across the Co3p–Co3d photoionization threshold. We have observed that the resonant enhancement of the photoemission intensity from the Co3d shell is not the same for samples with different cobalt content. We suggest that the Co3d contribution to the valence band depends on both Co and H content.

We report on the structural, electrical and magnetic properties of ZnCoO thin films grown by Atomic Layer Deposition (ALD) 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 300oC 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 SIMS, SEM, EDS, XRD, AFM, Hall effect and SQUID investigations.