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In order to effectively utilize the photovoltaic properties of gallium arsenide, its surface/interface needs to be properly prepared. In the experiments described here we examined eight different paths of GaAs surface treatment (cleaning, etching, passivation) which resulted in different external quantum efficiency (EQE) values of the tested photovoltaic (PV) cells. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) examinations were conducted to obtain structural details of the devices. X-ray photoelectron spectroscopy (XPS) with depth profiling was used to examine interface structure and changes in the elemental content and chemical bonds. The photoluminescence (PL) properties and bandgap measurements of the deposited layers were also reported. The highest EQE value was obtained for the samples initially etched with a citric acid-based etchant and, in the last preparation step, either passivated with ammonium sulfide aqueous solution or treated with ammonium hydroxide solution with no final passivation. Subsequent I–V measurements, however, confirmed that from these samples, only the sulfur-passivated ones provided the highest current density. The tested devices were fabricated by using the ALD method.

ZnO implanted with Rare Earth (RE) ions has a potential application as phosphor or in white light sources. The paper discusses the structural, optical and electrical changes caused by Yb, Dy and Pr ions implanted into thin ZnO films grown by Atomic Layer Deposition (ALD). Using channeling Rutherford Backscattering Spectrometry (RBS/c), room temperature photoluminescence (RT PL) technique and Hall effect measurements, it has been shown that the initial damages of the ZnO crystal lattice caused by the rare earth (RE) ion implantation can to a certain extent be removed via post-implantation thermal treatment, provided the fluence is lower than 1.5 × 1015 at.cm−2. A comparison of the structural optical and electrical properties of annealed ALD–ZnO:RE layers with the results of analogous studies performed on thermally untreated RE-implanted films allows us to conclude that properly selected annealing steps allow for a substantial improvement in the conductivity of the layers as well as the intensity of luminescence, which can be attributed to the appearing recrystallization phenomena in the ZnO lattice.

Zinc oxide is nowadays widely investigated in many different science areas. In particular, this wide band gap semiconductor is valued due to its possible use in transparent electronics as TCO (Transparent Conductive Oxide) and/or as ARC (Antireflective Coating). In other applications, ZnO can also play active role in light source devices, UV detectors, solar cells, etc. In this experiment we focused on zinc oxide applicability assessment in solar cell devices. ZnO as well as its Al-doped form AZO (Aluminum doped Zinc Oxide) were examined in view of their use both as TCO and the n-type partner for the p-type gallium arsenide (GaAs) substrate, that resulted in creation of the p-n heterojunction-based photovoltaic device. In order to deposit both ZnO as well as AZO layers, the ALD (Atomic Layer Deposition) method was applied.

Vertical structures based on Pd Schottky contacts to a ZnO/AZO bilayer have been realized and electrically characterized. Following a preliminary annealing study on the separated ZnO and AZO layers the ZnO/AZO bilayer was first annealed at 450 °C for 30 min to reduce the carrier concentration and then functionalized with a H2O2 dip prior to Pd deposition. On the basis of Atomic Force Microscopy, Transmission electron Microscopy and Capacitance vs Voltage measurements it has been found that the H2O2 treatment lowers the surface roughness and creates a ~ 200 nm thick layer formed by ZnO crystallites with grain size ≲ 10 nm embedded into an amorphous matrix with reduced carrier concentration. However, contrary to what previously reported no formation of ZnO2 has been observed. The obtained Schottky contacts showed a rectification ratio ≳ 10 2 at −2 V/+2 V with a detailed analysis based on the differential approach pointing to field enhanced emission from defective channels as the main leaking mechanisms.

Electric measurements were performed on solar cells composed of n-type ZnO nanorods grown by the hydrothermal method on p-type silicon substrate. The nanorods were covered with silver nanoparticles of sizes 20–30 nm and 50–60 nm. The diameters and density of the nanorods and nanoparticles were determined from scanning electron microscopy (SEM) and atomic force microscopy (AFM) images. On top of the structures the ZnO:Al (AZO) layer was deposited as a transparent electrode using the atomic layer deposition (ALD) method. The efficiency of the cells was found to be ∼3.4%, however the sample with larger nanoparticles exhibit better performance. The analysis of the current-voltage (I-V) measurements vs illumination intensity let us conclude that the surface recombination deteriorates their performance. The measurements of capacitance-voltage (C-V) characteristics allowed us to determine the concentration of donors in ZnO and built-in voltage at the ZnO/Si interface. The deep level transient spectroscopy (DLTS) measurements confirmed the presence of defects at the surface as well as deeper in the ZnO nanorods. Obtained results compared with the data reported elsewhere let us conclude that the defect density is much less than in the case of similar heterojunction ZnO/Si solar cells made by other technological methods.

In order to improve the efficiency of a solar cell based on silicon, one must find a compromise between its price and crystalline quality. That is precisely why the knowledge of defects present in the material is of primary importance. This paper studies the defects in commercially available cheap Schottky titanium/gold silicon wafers. The electrical properties of the diodes were defined by using current–voltage and capacitance–voltage measurements. Low series resistance and ideality factor are proofs of the good quality of the sample. The concentration of the acceptors is in accordance with the manufacturer’s specifications. Deep level transient spectroscopy measurements were used to identify the defects. Three hole traps were found with activation energies equal to 0.093 eV, 0.379 eV, and 0.535 eV. Comparing the values with the available literature, the defects were determined as connected to the presence of iron interstitials in the silicon. The quality of the silicon wafer seems good enough to use it as a substrate for the solar cell heterojunctions.

This paper is devoted to the electrophysical diagnostics of the ZnO-based rectifying structures in which the semiconducting oxide layer has been obtained by the low-temperature (80 °C ≤ T ≤ 130 °C) Atomic Layer Deposition (ALD) process. For the growth of examined diodes an organic compound (diethylzinc, DEZn) was used as a zinc precursor. As an oxygen source either deionized (in case of Schottky rectifiers as well as for n-type part of homojunction) or ammonia water (for the p-type layer of homojunction) was applied. In order to improve the basic electrical parameters of these structures (with a particular interest in the rectification (ION/IOFF) ratio) a solution based on inserting the thin dielectric layer (HfO2 or Al2O3) either below the Ag Schottky contact or between the homodiode parts, respectively, has been tested. Through comparing the electrical properties of Ag/HfO2/ZnO/ITO Schottky diodes and ZnO homojunctions as well as modeling their room-temperature current–voltage (I–V) characteristics according to the differential approach it has been proven that the optimal interlayer thickness allowing to achieve the ION/IOFF parameter as high as 104–105 for approximately ± 2 V polarization voltage range is about 2.5–5-nm. Additionally, involving the theoretical studies, the dominant carrier transport mechanisms were identified to be the monopolar injection, tunneling/trapping phenomena occurring in the dielectric layer and bimolecular recombination. The achieved results predestine the examined structures to be applied in the modern electronic devices, where stable in time and good quality diodes are required.

Conventional deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques were used to study electrical properties of deep-level defects in dilute GaNAs epitaxial layers grown by atmospheric-pressure metalorganic vapourphase epitaxy (APMOVPE) on the GaAs substrate. Three samples with nitrogen concentrations of 1.2 %, 1.6 % and 2.7 % were investigated. In DLTS and LDLTS spectra of the samples, four predominant electron traps were observed. On the basis of the obtained electrical parameters and previously published results, one of the traps was associated with N-related complex defects, while the other traps with common GaAs-like native defects and impurities, called EL6, EL3 and EL2.

Zinc oxide (ZnO) films were used in silicon-based photovoltaic (PV) structures both as an n-type partner to p-type Si and (on top) as a transparent electrode (as a so-called TCO film). Photovoltaic response of such PV structures depends on the electrical properties of n-ZnO films as well as p-Si (100) substrates. The ZnO-based TCO films were deposited by an Atomic Layer Deposition (ALD) method. The films show a high electron concentration (~10 20 cm −3 ) and a relatively high electron mobility (>10 cm 2 /V s). Considering Si, we used fairly cheap commercial substrates with 360 µm thickness, i.e., not optimized for PV cells applications. The best results were obtained for Si substrates with a moderate hole concentration (~10 15 cm −3 ) and resistivity of 10 Ω cm. The photovoltaic efficiency achieved is 4.4%, with the possibility of further improvement.

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.

Properties of UV detector based on ZnO nanorods, grown by a hydrothermal method, are discussed. The innovative growth technology was used to produce ZnO nanorods. It is characterized by a much higher growth rate, than reported (till now) in the literature, and a very low costs (both of technology and materials). Importantly, ZnO nanorods grown by this method are free from oxygen vacancies. Despite the fact that detector proposed by us is not based on a single nanorod, but on a whole array of nanorods, it is very sensitive. The detector shows sensitivity of 20 mW/m2 (2 µW/cm2) upon UV illumination. Due to a high energy band gap of zinc oxide and a high purity of the obtained nanorods visible light is not detected. The resistivity/current changes are proportional to illumination intensity, i.e., detector response scales with the intensity of UV light. The observed changes of the detector resistivity relate to surface reactions generated upon an illumination. Importantly, detector does not need annealing or cleaning to reset to an initial state.(© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High quality heterojunctions based on dual acceptor doped ZnO:(As,Sb) films grown on n-type GaN templates were used for UV detector application. Photodetectors made on the obtained diodes appeared to have a high selectivity in the UV spectral range. Photocurrent measurements revealed a very narrow response window of ∼12 nm only. The difference between the dark and bright current was large and the ratio of these currents was about 103. The response time of the detectors is shorter than 1 ms.

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%.

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.

Monocrystalline films of sphalerite-type ZnSe were grown on GaAs(100) substrates from elemental Zn and Se precursors by atomic layer epitaxy in a gas flow system. Due to color mixing of band edge and deep defect-related emissions these layers emit intensive white light. Depth profiling cathodoluminescence indicates that green and red emissions mostly come from disordered regions of the films, close to the ZnSe/GaAs interface. We tested a possibility of tuning of chromaticity coordinates and of color temperature of the emission. We found that the chromaticity parameters (color perception) can be tuned by either regulating the appropriate accelerating voltage of electrons or current density of primary electrons in cathodoluminescence investigations. These properties of ZnSe films make them suitable for some practical applications as white light sources.

We studied epitaxial growth conditions of II—VI semiconductors on (110) substrates, which is indispensable for fabrication of T-shaped quantum wire structures. We experimented with different types of (110)-oriented substrates and monitored the surface quality of deposited layers in situ by reflection high energy electron diffraction and ex Situ by photoluminescence. The aim of this work is to find optimum growth conditions of II—VI compounds on a cleaved edge of a superlattice as required by the overgrowth method.

ZnO films with high conductivity are obtained by atomic layer deposition for the application in solar cells based on CdS/CdTe/Cu2S films. The parameters of solar cells with ZnO electrode are compared with the ones with Mo. The advantages of ZnO electrode are discussed.

Electrical and charge trapping properties of atomic layer deposited HfO2-Al2O3 multilayer stacks with two different Al2O3 sublayer thicknesses were investigated regarding their implementation in charge trapping non-volatile memories. The effect of post deposition annealing in oxygen at 600°C is also studied. The decreasing Al2O3 thickness increases the stack's dielectric constant and the density of the initial positive oxide charge. The initial oxide charge increases after annealing to ~6×1012 cm-2 and changes its sign to negative for the stacks with thicker Al2O3. The annealing enhances the dielectric constant of the stacks and reduces their thickness preserving the amorphous status. Nevertheless the annealing is not beneficial for the stacks with thicker Al2O3 as it considerably increases leakage currents. Conduction mechanisms in stacks were considered in terms of hopping conduction at low electric fields, and Fowler- Nordheim tunnelling, Schottky emission and Poole-Frenkel effect at higher ones. Maximum memory windows of about 12 and 16V were obtained for the as-grown structures with higher and lower Al2O3 content, respectively. In latter case additional improvement (the memory window increase up to 23V) is achieved by the annealing.

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.

ZnO layers have been grown by atomic layer epitaxy using a gas flow version of the technique. ZnO films have been obtained from either a double exchange chemical reaction, a single exchange reaction, or from elemental components, i.e., from zinc and oxygen. We have also studied ZnO layers prepared by the oxidisation of ZnS layers. Silicon ([001] and [111]), GaAs, sapphire, sapphire/GaN or soda lime glass substrates have been used. We demonstrate that ZnO films are suitable as buffer layers for GaN epitaxy.

We witness a new revolution in electronic industry — a new generation of integrated circuits uses as a gate isolator HfO2. 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.

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.

We demonstrate that the atomic layer deposition (ALD) technique has large potential to be widely used in a production of ZnO films for applications in electronic, photovoltaic (PV) and optoelectronic devices. Low growth temperature makes the ALD-grown ZnO films suitable for construction of various semiconductor/organic material hybrid structures. This opens possibilities of construction of novel devices based on very cheap organic materials. This includes organic light emitting diodes and PV cells of the third generation, as discussed in the present work.