K. Kopalko

Extremely low temperature growth of ZnO by atomic layer deposition

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.

ZnO grown by atomic layer deposition: A material for transparent electronics and organic heterojunctions

We report on zinc oxide thin films grown by atomic layer deposition at a low temperature, which is compatible with a low thermal budget required for some novel electronic devices. By selecting appropriate precursors and process parameters, we were able to obtain films with controllable electrical parameters, from heavily n-type to the resistive ones. Optimization of the growth process together with the low temperature deposition led to ZnO thin films, in which no defect-related photoluminescence bands are observed. Such films show anticorrelation between mobility and free-electron concentration, which indicates that low n electron concentration is a result of lower number of defects rather than the self-compensation effect.

Zinc oxide for electronic, photovoltaic and optoelectronic applications

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.

The influence of growth temperature and precursors' doses on electrical parameters of ZnO thin films grown by atomic layer deposition technique

In this paper we report on the low-temperature growth (Ts=30-250^oC) of zinc oxide thin films by atomic layer deposition method using two different organic zinc precursors: diethylzinc and (for comparison) dimethylzinc, and deionized water as an oxygen precursor. An evident influence of growth temperature and precursors" doses on electron concentration and Hall mobility of obtained zinc oxide layers is presented. The lowest achieved room-temperature electron concentration was at the level of 10^1^6cm^-^3 with mobility up to 110cm^2/Vs.

Magnetic properties of ZnMnO films grown at low temperature by atomic layer deposition

The authors demonstrate that by lowering deposition temperature of ZnMnO films (T<500°C) they can avoid Mn clustering and creation of inclusions of Mn oxides, which are frequently formed in ZnMnO layers grown by high temperature methods. Low temperature growth is achieved using atomic layer deposition and organic zinc and manganese precursors.

Low temperature growth of ZnMnO: A way to avoid inclusions of foreign phases and spinodal decomposition

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.

Nitrogen doped p-type ZnO films and p-n homojunction

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.

Photovoltaic properties of ZnO nanorods/p-type Si heterojunction structures

Summary 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%.

ZnO, ZnMnO and ZnCoO films grown by atomic layer deposition

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.

N and Al co-doping as a way to p-type ZnO without post-growth annealing

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.