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The structural, optical, and electrical properties of ZnO are intimately intertwined. In the present work, the structural and transport properties of 100 nm thick polycrystalline ZnO films obtained by atomic layer deposition (ALD) at a growth temperature (Tg) of 100–300 °C were investigated. The electrical properties of the films showed a dependence on the substrate (a-Al2O3 or Si (100)) and a high sensitivity to Tg, related to the deviation of the film stoichiometry as demonstrated by the RT-Hall effect. The average crystallite size increased from 20–30 nm for as grown samples to 80–100 nm after rapid thermal annealing, which affects carrier scattering. The ZnO layers deposited on silicon showed lower strain and dislocation density than on sapphire at the same Tg. The calculated half crystallite size (D/2) was higher than the Debye length (LD) for all as grown and annealed ZnO films, except for annealed ZnO/Si films grown within the ALD window (100–200 °C), indicating different homogeneity of charge carrier distribution for annealed ZnO/Si and ZnO/a-Al2O3 layers. For as grown films the hydrogen impurity concentration detected via secondary ion mass spectrometry (SIMS) was 1021 cm−3 and was decreased by two orders of magnitude after annealing, accompanied by a decrease in Urbach energy in the ZnO/a-Al2O3 layers.

The impact of hydrogen in ZnO is revealed by combining reaction dynamics calculations with temperature dependent Hall (TDH), photoluminescence, and secondary ion mass spectrometry measurements performed on H, 2H, and He implanted ZnO. H and 2H box profiles with a concentration ranging from ∼ 3 × 10 17 cm − 3 to ∼ 10 19 cm − 3 and He to produce as much as damage as in the [H] ∼ 3 × 10 17 cm − 3 case were implanted in the samples. The formation of Li lean regions has been observed for [ 2H] < 10 19 cm − 3 after annealing at 400 °C. This is attributed to Li i presence consequent to the diffusion of Zn i created during the H/ 2H implantation process. Results extracted from the TDH measurements performed prior to the annealing at 400 °C evidence that Li i contributes to an increase in carrier concentration up to ∼ 10 17 cm − 3 by providing a donor level with an activation energy of ∼40 meV and thus is very close to the value of ∼47 meV expected for H in the oxygen site. The reaction dynamics analysis evidences that the amount of Li i introduced is decreasing at higher H implantation doses as a result of increasing V Zn and H-V Zn retrapping, reactions in which Li i is competing with H. Overall, due to Li i formation as well as the presence of Al the maximum percentage of the implanted H or 2H acting as a donor in the investigated range is found to be ≲ 2%, which is considerably lower than previously reported.

The theoretical approach towards improving the photovoltaic response of n-ZnO/p-Si heterojunctions proposed by Knutsen et al. [Phys. Status Solidi A 210 (2013) 585–588] has been experimentally tested. AZO/n-Zn(1−x)MgxO layers were deposited at 160 °C on p-Si substrates by atomic layer deposition (ALD) with magnesium concentration in the 0–4 at% range. The examined devices showed a reduction of the conduction band offset from (0.63±0.03) eV to (0.48±0.03) eV. This decrease leads to a diminishing impact of recombination centers at the interface between zinc oxide based layers and silicon substrate, when the Mg content is below ~1.6 at%. In this range, the overall photovoltaic efficiency increased from ~3.7% to ~6.0%. As a next step, we tested solar cells with similar magnesium concentration in the Zn(1−x)MgxO layer, but deposited at 300 °C. Due to the higher deposition temperature, a further 1.1% increase in efficiency has been obtained. So far, this is the highest reported efficiency for a ZnO/Si heterojunction grown by ALD method, thus experimentally confirming the validity of the approache s here studied for raising the efficiency of heterojunctions solar cells based on n-ZnO/p-Si, while significantly reducing the fabrication complexity respect to conventional Si based devices as emphasized by Hussain et al. [Sol. Energy Mater. Sol. Cells 139 (2015) 95–100].

Arsenic-doped ZnO films were formed by thermal annealing of epitaxial ZnO films grown by Atomic Layer Deposition (ALD) in arsenic atmosphere at temperature 850–950 °C. X-ray photoelectron spectroscopy (XPS) studies of the ZnO:As films revealed the complex As3d core level spectra formed by three components located at about 41 eV, 45 eV and 47.5 eV below the Fermi level. The As3d component at binding energy (BE) of 45 eV was found to be correlated with the acceptor bound A°X exciton state observed in low temperature photoluminescence. This observation strongly supports the previously postulated assumption that the origin of the 45 eV component of the As3d spectra can be ascribed to arsenic atoms in As Zn –2V Zn complexes formed as a result of high temperature annealing. This assumption is also supported by the evident valence band shift towards the Fermi level in the ZnO:As film annealed at 950 °C.

In this paper we report on the optical and electrical studies of single GaAs1−xNx epitaxial layers grown on GaAs substrates by means of atmospheric pressure metal organic vapour phase epitaxy (APMOVPE). Three kinds of samples with 1.2 %, 1.6 % and 2.7 % nitrogen content were studied. Optical properties of the layers were investigated with the use of room temperature transmittance and reflectance measurements. Subsequently Schottky Au-GaAs1−xNx contacts were processed and characterized by current-voltage (I-V) and capacitance-voltage (C-V) measurements within 80–480 K temperature range. From the I-V and C-V characteristics the ideality factor, series resistance and built-in potential were determined. Obtained diodes can be used for further studies on defects with the use of DLTS method.

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 degrees 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. (C) 2011 Elsevier Ltd. All rights reserved. (Less)

In the present work we report on the monocrystalline growth of (00.1) ZnO films on GaN template by the Atomic Layer Deposition technique. The ZnO films were obtained at temperature of 300 °C using dietylzinc (DEZn) as a zinc precursor and deionized water as an oxygen precursor. High resolution X-ray diffraction analysis proves that ZnO layers are monocrystalline with rocking curve FWHM of the 00.2 peak equals to 0.07°. Low temperature photoluminescence shows a sharp and bright excitonic line with FWHM of 13 meV.

This paper reports on the electrical and optical properties of zinc oxide thin films grown at the temperature range between 160 and 240 °C by the atomic layer deposition method using diethylzinc (Zn(C 2 H 5 ) 2 , DEZn) and deionized water precursors. Silicon and glass were used as substrates for the ZnO growth. These films were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), low temperature photoluminescence (LT PL) and low temperature Hall effect measurements. This analysis revealed that all the obtained as-grown ZnO layers are fairly smooth (with a roughness RMS parameter less than 4 nm), show a metallic-like conductivity, exhibited a carriers' concentration (n) of 10 19 -10 20 cm -3 which was found to be practically independent of temperature between 7 and 300 K. From the LT PL spectra, it was established that the carriers' concentration is nearly inversely proportional to the intensity of the LT PL edge emission peak. These observations, together with the fact that the Hall mobility slightly increases at higher temperatures, indicate the existence of a competitive scattering mechanism (on grain boundaries as well as on ionized impurities). However, ionized impurity scattering seems to be the dominant factor limiting the carrier mobility in the discussed case. Moreover, the results suggest that efficient non-radiative Auger processes are responsible for the observed photoluminescence (PL) quenching in the samples with higher electron concentration.

Magnetic, structural, and optical properties of ZnMnO films grown with atomic layer epitaxy are discussed. Atomic layer epitaxy films were grown at low temperature using organic zinc and manganese precursors. From magnetometry and electron spin resonance investigations we conclude that lowering of a growth temperature significantly limits formation of Mn precipitates and inclusions of different foreign phases of manganese oxides to ZnMnO host.

The electronic band structure of Mn/ZnTe(110) (1×1) has been studied by angle-resolved photoelectron spectroscopy. The sets of spectra were acquired for the clean surface and after in situ deposition of 0.4 ML of Mn, in order to compare the band structures and to reveal changes brought about by the presence of Mn. The experimental band structure diagram of Mn/ZnTe along the Γ−K direction in the Brillouin zone has been derived from the experimental data. Indications of interaction between the Mn 3d states and sp bands of the semiconductor are discussed.

The Mn/ZnO(0001) system was investigated by synchrotron radiation photoemission. The Mn/ZnO interface with 4 ML of manganese deposited onto the ZnO surface was annealed up to 500◦C. No Mn capping layer was found at the surface after annealing as was confirmed by scanning Auger spectroscopy experiment. We used a resonant photoemission to extract the Mn3d partial density of states in photoemission spectra. The Mn3d states contribute to the electronic structure of the system within 10 eV of the Fermi level. They show three features: a main peak at 3.8–4.5 eV, a valence structure at the top of the valence band (1–3 eV), and a broad satellite situated between 5.5 and 9 eV below EF. The satellite/main branching ratio was determined to be 0.43, which is a fingerprint of strong hybridization between the Mn3d electrons and the valence band of the crystal. The hybridization effect in Zn1−xMnxO surface alloy is comparable to Zn1−xMnxS and much higher than in Zn1−xMnxSe, Zn1−xMnxTe, and Ga1−xMnxAs semimagnetic compounds.

The electronic structure of monocrystalline ZnTe was investigated for a clean, relaxed ( 110)-(1 x 1) surface and for the same surface after sequential deposition of Mn atoms. The resonant (Fano-type) photoemission technique was applied. The spectra were measured as energy distribution curves and in the constant initial state mode, for the valence band and Zn 3d core level. At very low Mn coverage (θ < 0.15 nm), manganese interaction with the crystal surface results in creation of ternary alloy Zn 1-x Mn x Te(110) surface. Further increasing of Mn deposition leads to formation of metallic manganese islands on the surface. The successive annealing leads to Mn atoms diffusion and to formation of Zn 1-x Mn x Te at the surface region.

Atomic layer epitaxy (ALE) of ZnO on a GaN template was performed in a low-pressure gas flow system using ZnCl2 and O2 precursors, and the evidence of monocrystallinity of an ALE-grown ZnO film is presented. The growth is achieved under the pressure of about 5 mbar with 480 °C substrate temperature and the ZnCl2-source temperature of 390 °C. According to the AFM analyses, the film surface exhibits a low roughness value of 0.45 nm RMS, which fulfills the expectations with respect to high morphological quality of the ALE products. The structural properties of the produced ZnO are characterized by means of X-ray diffraction methods based on wide range 2θ/ω scans and high-resolution studies of 00.2 and 11.4 reciprocal lattice points. Lattice parameters for ALE-grown ZnO layer are a = 0.3253(1) nm and c = 0.52060(5) nm, as derived from the high-resolution data. The mosaicity level of the GaN template layer is reproduced in the grown ZnO film.

We present the results of photoemission studies on (0 0 0 1 ) (N-polar) surfaces of bulk gallium nitride crystals. The procedures that yield clean and well-ordered (0 0 0 1 ) (1×1) surfaces were developed and tested. The surface crystallinity was assessed by low-energy electron diffraction. Angle-resolved photoemission spectroscopy with synchrotron radiation was used to determine the valence-band electronic structure of GaN along the Γ – Δ – A direction of the Brillouin zone. The band structure derived from our experimental data is compared with the results of recent band structure calculations.

We demonstrate experimental results on p-type ZnO films grown by atomic layer deposition (ALD) and co-doped with aluminum and nitrogen (ANZO). The films were obtained at low temperature (100 °C) with different N to Al ratio and show conductivity type, which depends on the N and Al content. We applied the x-ray photoelectron spectroscopy in order to get insight into a chemical nature of dopants and we found three pronounced contributions of the N1s core level which appear at binding energies of 396.1, 397.4 and around 399 eV. Based on ANZO and undoped ZnO films, both grown by the ALD technique, the ZnO homojunction was obtained in one technological process without any post-growth high temperature processing. The rectification ratio as high as 4 × 104 at ± 2 V was achieved when an ultrathin Al2O3 layer was inserted between p- and n-type ZnO and a n-type ZnO buffer layer deposited on an insulating Si substrate was applied.

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.

The new type of a p-i-n structure consists of a single acceptor doped ZnO:N film grown by plasma assisted molecular beam epitaxy, a thin isolating Al2O3 layer grown by atomic layer deposition method and n-type GaN template. The maximum forward-to-reverse current ratio I F/I R in the obtained diode is about 8 × 106 at ±7 V. Electron-beam-induced current measurements confirmed the presence of a p-i-n junction and the presence of the isolating layer located at the p-ZnO/n-GaN interface. The diffusion length of carriers was calculated. The heterostructure exhibits an absorption in the UV range and the ratio between light (UV) and dark current is above four orders of magnitude.

Electronic structure of Mn/ZnO system has been investigated by synchrotron radiation photoemission. Manganese vacuum deposition was done at room temperature onto a ZnO(0001) single crystal for coverage ΘMn < 4 ML. Photoemission spectra taken near Mn3p-Mn3d absorption edge after each deposition step show resonant enhancement of Mn3d states within 10 eV of the Fermi level. The experimentally deduced partial Mn3d density of states for Θ > 1.2 ML shows at least three features: a major Mn3d structure at 3.8–4.5 eV below the Fermi energy, a valence structure at lower binding energy (1–3 eV) and a broad satellite in the 5.5 – 9 eV range. The branching ratio of satellite/main structure increases with deposition from 0.33 for 0.4 ML to 0.65 for 4 ML. After annealing up to 500 C the satellite/main ratio decreases to 0.43 indicating a high degree of hybridization between the Mn3d states and valence band of ZnO. After annealing no manganese cap layer was found at the crystal surface as was confirmed by the lack of metallic Fermi edge in photoemission spectra and by scanning Auger spectroscopy experiment. The photoemission Mn3p core level spectra taken after annealing consist of two components separated by about 4eV. It is evidence that at least two manganese states are observed in the Mn-ZnO interface region.

Summary form only given. We evaluate structural quality and surface morphology of ZnS films grown by ALE. We study influence of film morphology and of growth conditions on optical properties of these films. Results of atomic force microscopy (AFM), scanning electron (SEM) and cathodoluminescence (CL) microscopy and of photoluminescence (PL) investigations of ZnS layers grown on GaAs substrates by three different methods are discussed.

We demonstrate the ZnO homojunction fully obtained by the atomic layer deposition technique at low temperature growth of 100?130 ?C. For the n-type partner of the junction we used undoped ZnO film obtained at 130 ?C, while nitrogen doped ZnO acted as the p-type partner of the junction. Nitrogen was introduced into the ZnO film during the ALD process by using ammonia water as an oxygen precursor and diethylzinc as a zinc precursor. The p-type conductivity of ZnO was activated by the subsequent annealing of the ZnO:N film in an oxygen or nitrogen atmosphere. The initial rectification ratio of 102 at ?2 V was raised to 4???104 by inserting an ultrathin Al2O3 layer between p- and n-type ZnO. The resulting rectification ratio is among the best parameters reported for a ZnO homojunction so far.

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.

The electronic structure of ferromagnetic (Zn,Co)O lms 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 lms were grown by atomic layer deposition at temperature between 160 ◦C and 300 ◦C and they di ered 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 di erence 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 lms di ers signi cantly from that of the lms which show the paramagnetic response.

We report on the zinc oxide (ZnO) thin films obtained by the atomic layer deposition (ALD) method using diethyl zinc and water precursors, which allowed us to lower deposition temperature to below 200 °C. The so-obtained “as grown” ZnO layers are polycrystalline and show excitonic photoluminescence (PL) at room temperature, even if the deposition temperature was lowered down to 100 °C. Defect-related PL bands are of low intensity and are absent for layers grown at 140−200 °C. This is evidence that extremely low temperature growth by ALD can result in high quality ZnO thin films with inefficient nonradiative decay channels and with thermodynamically blocked self-compensation processes.

The authors demonstrate herein that by lowering of a growth temperature they can obtain ZnMnO layers with homogeneous Mn distribution, which are free of Mn accumulations and inclusions of foreign phases due to other Mn oxides. These layers (with low Mn content fractions) show paramagnetic phase in room temperature magnetization measurements. Contribution of a high temperature ferromagnetic phase is missing, which the authors relate to blocking of spinodal decomposition of ZnMnO under controlled growth conditions of atomic layer deposition.

The electronic structure of Mn/ZnO system has been invesigated by synchrotron radiation photoemission. Manganese vacuum deposition was done at room temperature onto a ZnO(0001) single crystal for coverage Mn-Theta = 1.2 ML shows at least three features: a major Mn3d structure at 3.8-4.5 eV below the Fermi edge, a valence structure at lower binding energy (1-3 eV) and a broad satelite in the 5.5-9 eV range. The branching ratio of satellite/main structure increases with depostion from 0.33 for 0.4 ML to 0.65 for 4 ML. After annealing up to 500 degrees C the satellite/main ratio decreases to 0.43 indicating a high degree of hybridization between the Mn3d states and valence band of ZnO. After annealing no manganese cap layer was found at the crystal surfaces as was confirmed by the lack of metallic Fermi edge in photoemission spectra and by scanning Auger spectroscopy experiment. The photoemission Mn3p core level spectra taken after annealing consist of two components separated by about 4 eV, which shows that at least two manganese states are observed in the Mn-ZnO interface region. (Less)