Bandgap engineered ZnSxO1-x films were grown on Fluorinated Ethylene Propylene (FEP) substrates and analyzed using transmission spectroscopy. FEP is considered as a potential substrate for application in flexible electronics and semiconductor films.

Potassium (K) ions have been implanted in hydrothermally grown ZnO to a dose of 1 × 1015 cm-2, followed by isochronal annealing in a tube furnace (30min) and by rapid thermal annealing (30s) on two separate samples. For annealing temperatures below 700°C, only a minor redistribution of Li is observed behind the projected range of the K+ ions. At temperatures between 700 and 750°C, however, both annealing treatments show a wide region behind the implantation peak which is depleted of Li, and this depletion is used as a tracer to monitor diffusion of intrinsic defects like the Zn interstitial. The results are interpreted as Zn interstitials being released from the implanted region in a burst at temperatures above ∼700°C, followed by rapid migration, replacement of Li on Zn site through the kick-out mechanism, and migration of Li away from the active region.

Aluminum-doped zinc oxide (ZnO:Al) thin films were prepared on glass substrates by radio frequency (RF) magnetron sputtering from a ceramic mixed target ZnO:Al2O3 (1 wt.%) with a power of 250 W. Two series of samples were deposited at room temperature, the first one in pure Ar atmosphere, the second one in Ar/O2 gas mixture. Effects of post-deposition annealing treatments carried out from 400 °C to 500 °C under vacuum and in N2/H2 (5%) atmosphere have been investigated. The influence of these parameters was studied by a detailed microstructural analysis using X-Ray diffraction and Raman spectroscopy. For N2/H2 annealing process, the increase of charge carrier concentration limits the increase of the mobility while after vacuum annealing, an improvement of both electrical and optical properties was observed. The increase of the crystallinity and grain size for ZnO:Al films deposited in Ar/O2 gas mixture could explain their improvements. Resistivity was reduced down to 3.5×10-4 Ω.cm, for a mobility of 49 cm2/V.s with a vacuum annealing at 450 °C for ZnO:Al deposited in Ar/O2 gas mixture.

Conventional phosphor materials are doped ternary or quaternary compounds; hence it would be difficult to prepare nanoparticles of those materials by build up methods. Ba2ZnS3:Mn (BZS), SrGa2S4:Eu, and BaAl2S4:Eu nanoparticles were prepared by a break down method, namely the ball-milling method. Transmission electron microscopy (TEM) and TEM- energy-dispersive X-ray spectroscopy (EDX) measurements showed several-nanometer-size stoichiometric and dispersed nanoparticles were achieved. ZnO-coating was performed and the uniform coating layers were formed on the phosphor nanoparticles. The ZnO-coated nanoparticles exhibited an improved stability in Photoluminescence. Red color phosphor material, namely BZS, was ball-milled and sprayed on the glass substrate. Mn doped BZS absorbs ultra violet light and emits red light peaking at around 640nm. When the single crystal Si solar cell was placed under the transparent nanoparticle layer, short wavelength light was absorbed and converted to long wavelength light.

We report apparent robust doping of ZnO and MgxZn1-xO (x ∼20%) nanoparticle films by annealing in hydrogen gas. The annealing was done at sequentially higher temperatures from about 20 °C to 140 °C. The effect of the annealing was determined by comparing current-voltage measurements of the samples at room-temperature and in vacuum after each annealing cycle.The nanoparticles were grown using an aqueous solution and heating process that created thinfilms of ZnO or MgZnO nanoparticles with diameters of about 30 nm. When exposed to hydrogen gas at room-temperature or after annealing at temperatures up to about 100 °C, no measureable changes to the room-temperature vacuum conductivity of the films was observed. However, when the samples were annealed at temperatures above 100 °C, an appreciable robust increase in the room-temperature conductance in vacuum occurred. Annealing at the maximum temperature (∼135-140 °C) resulted in about a factor of about twenty increase in the conductivity. Furthermore, the ratio of the conductance of the ZnO and MgZnO nanoparticle films while being annealed to their conductance at room-temperature were found to increase and then decrease for increasing annealing temperatures. Maximum changes of about five-fold and seven-fold for the MgZnO and ZnO samples, respectively, were found to occur at temperatures just below the annealing temperature threshold for the onset of the robust hydrogen gas doping. Comparisons of these results to other work on bulk ZnO and MgZnO films and reasons for this behavior will be discussed.

Thin films of zirconium oxide (ZrOx) and hafnium oxide (HfOx) were rf sputtered onto fused silica substrates in an oxygen rich argon environment. Pure zirconium and hafnium targets were used, and the oxygen partial pressure was varied to control the oxygen stoichiometry. Measurement of the EPR characteristics of the ZrOx films indicated two peaks corresponding to two orientations of the magnetic field. This anisotropic response suggested the films were polycrystalline with a preferred orientation. This was confirmed by XRD pole figures. The measured g-values for the ZrOx films were less than the free-spin g-value, indicating the defects corresponded to electron traps. It was further shown that the lower the oxygen partial pressure during deposition, the larger the EPR response, strongly suggesting the traps correspond to oxygen vacancies in ZrOx. Hafnium oxide thin films were also characterized by EPR. The EPR measurements indicated the presence of a single resonance peak, suggesting these films were polycrystalline without a preferred orientation or amorphous. XRD measurements confirmed that the HfOx films were amorphous. The g-value for these films was greater than that the free-spin value, indicating the presence of possibly self-trapped oxygen hole centers. These results will be discussed in the context of prior experimental and theoretical work on these systems.

In this work, we study the effects of implanted hydrogen ions on defect formation and impurity redistribution in ZnO crystals implanted with silver ions. Hydrogen was first implanted at room temperature in ZnO with energy of 30 keV to a dose of 2 × 1016 /cm2. The ZnO samples with and without prior H implantation were implanted with Ag ions at four different energies, 30, 75, 150, and 350 keV, to doses 3.3×1013, 4.2×1013, 8.3×1013 and 3.4×1014 /cm2, respectively, resulting in a uniform concentration profile of Ag from the surface to depth ~ 150 nm. These samples were annealed at temperatures 850-1050°C for 30 minutes in an oxygen gas flow. The distribution of Ag atoms, either aligned or nonaligned along the crystalline directions, were measured by Rutherford backscattering (RBS) combined with ion channeling. Following Ag ion implantation, the damage level in the ZnO lattice, measured along the <10-11> crystalline direction is higher in the sample without H ion implantation than the sample with H. Lattice damage was found to recover faster in the sample without H implantation than the sample with H, e.g., for Zn signals, the normalized RBS yield χmin for the without H-implanted sample dropped from 27.5% following Ag implantation to 4.3% after annealing at 1050 ˚C, whereas the Zn χmin value for the sample with H implant decreased from 17.6% following Ag implantation to 5.3% after annealing at 1050 ˚C. On the other hand, the χmin values for the Ag dopants before annealing in the H-implanted sample are the same in the sample without H. Post-Ag-implantation annealing resulted in much higher χmin values for Ag in the sample with H implant. For the as-implanted samples, 26.6% of the implanted Ag atoms are on substitutional sites in the sample with H, as compared to 30.3% of the implanted Ag being on the substitutional sites in the sample without H. After annealing at 1050 ˚C, the fraction of substitutional Ag is 73.7% in the H-implanted sample, in contrast to the fraction of 61.6% for substitutional Ag in the sample without H implant. Similar to other oxide crystals, H ion implantation and thermal annealing can result in the formation of nanocavities in the ZnO lattice. We discuss these findings in the context of the effects of nanocavities on formation and annihilation of point defects as well as on impurity diffusion and trapping in ZnO crystals.

Transparent p-n hetero-junction diodes are fabricated using, p-type NiO and n-type ZnO thin films deposited onto a Pt/Ti/glass substrate utilizing RF sputtering technique. The prepared hetero-junctions are studied for the structural, electrical and optical properties and the effect of post-deposition annealing is investigated through I-V measurements and XRD analysis. The as deposited hetero-junction is found to be giving ohmic behaviour while with post-annealing treatment it result in rectification with a ratio of forward-to-reverse current as high as 15 in the range -1.0 to 1.0 V. Forward threshold and the reverse breakdown voltages are found to be about 0.5 and -2.7 V, respectively. The forward-bias I-V characteristics are dominated by the flow of space-charge-limited current with an optical transmission of above 50 % in the visible region important for the transparent electronic device fabrication.

We report the results of photoluminescence measurements on ZnO bulk crystals implanted with both stable and radioactive species involving the group IV impurities Ge, Si and Sn. We previously confirmed the identity of a line emerging at 3.3225 eV as being related to Ge and present here uniaxial stress data which show that the defect responsible has trigonal symmetry. Experiments with Si provide circumstantial evidence of a connection with the well-known line at 3.333 eV. Our measurements indicate that for the case of Sn on the Zn site luminescence is not observed. We also confirm that the I9 and I2 lines are due to substitutional In impurities.

Room temperature magnetic properties of un-doped, as well as 10 at.% Fe-doped ZnO and MgO single-pass layer of ink-jet printed thin films have been investigated to obtain insight into the role of the band gaps and mechanisms for the origin of ferromagnetic order in these materials. It is found that on doping with Fe, the saturation magnetization is enhanced by several-fold in both systems when compared with the respective un-doped thin films. For a “28 nm thick film of Fe-doped ZnO (Diluted Magnetic Semiconductor, DMS) we observe an enhanced moment of 0.465μB /Fe atom while it is around 0.111μB/Fe atom for the doped MgO (Diluted Magnetic Insulator, DMI) film of comparable thickness. Also, the pure ZnO is far more ferromagnetic than pure MgO at comparable low film thicknesses which can be attributed to defect induced magnetism originating from cat-ion vacancies. However, the film thickness dependence of the magnetization and the defect concentrations are found to be significantly different in the two systems so that a comparison of the magnetism becomes more complex for thicker films.

TiO2 films with poly crystal were electrodeposited on conductive substrate (NESA glass, approximately 10Ω/□, Asahi glass Co. Ltd.) from the titanium potassium oxalate dehydrate aqueous solution containing hydroxylamine adjusted pH 9 with KOH aq. at 333k. The peak corresponded to Ti3+ion into these TiO2 film was not observed by using X-ray photoelectron spectroscopy (XPS). The photocatalysis of TiO2 film increased with a decrease of cathodic potential. In particular, TiO2 film obtained at cathodic potential of -1.3V, had the higher photocatalysis than that of other potential.

This study focused on structural and optical properties of ZnO films grown epitaxially on Gd3Ga5O12 substrates. ZnO films (a = 3.2439 Å and c = 5.2036 Å) were deposited on the (001) and (111) planes of Gd3Ga5O12 (GGG: a = 12.383 Å) garnet substrates by a pulsed laser deposition method. From out-of-plane and in-plane X-ray diffraction measurements, the obtained ZnO films showed a single phase with the (0001) orientation on the GGG (001) and (111) substrates. The epitaxial relations between the ZnO film and GGG (001) substrate were [10-10] ZnO ‖ [100] GGG and [10-10] ZnO ‖ [010] GGG, while the epitaxial relations between the ZnO film and GGG (111) substrate were [10-10] ZnO ‖ [11-2] GGG ±21°. Furthermore, transmittance electron microscopy revealed sharp interfaces between ZnO films and GGG substrates. From photoluminescent spectra, the ZnO films showed donor bound emissions superimposed with free excitons at a low temperature of 10 K.

We report on diffusion behavior for ion implanted indium and silver atoms in ZnO crystals. Both In and Ag ions were implanted at room temperature at 7-10° relative to c-axis to avoid channeling effects during implantation. In ions were implanted at four different energies (40, 100, 200, and 350 keV, respectively) and doses (4.20×1013, 6.70×1013, 8.10×1013 and 3.10×1014 /cm2, respectively), resulting in a total dose of 5 ×1014 /cm2. For another set of ZnO samples, Ag ions were implanted at energies 30, 75, 150, and 350 keV at doses 3.3×1013, 4.2×1013, 8.3×1013 and 3.4×1014 /cm2, respectively, to reach a total dose of 5×1014 /cm2. Both In and Ag implants resulted in a uniform concentration profile of the implanted dopants from surface to depth ~ 150 nm. The samples were annealed for 30 minutes at temperatures between 850-1050 °C in an oxygen gas flow. The distributions of In and Ag atoms, either aligned or nonaligned along the crystalline directions, were measured by Rutherford backscattering combined with ion channeling. The diffusivities for nonaligned (interstitial) and aligned (substitutional) dopants atoms were determined to vary with annealing temperature via the Arrhenius relationship. The diffusion activation energies (Ea) along the <10-11> direction for substitutional impurity atoms were lower than those for interstitial dopants atoms e.g., in the case of In, Ea ~ 1.52 eV for <10-11> aligned In atoms and Ea ~ 2.61 eV for interstitial In atoms between <10-11> atomic rows and in the case of Ag, Ea ~ 1.77 eV for the interstitial Ag atoms between the <10-11> atomic rows and 1.11 eV for <10-11> aligned Ag atoms. The diffusion activation energies showed a different trend for the two dopants as measured along the <0001> crystalline direction. For Ag implanted in ZnO, the activation energy of Ea ~ 0.91 eV for the aligned Ag atoms along <0001> direction and Ea ~ 1.55 eV were found for the interstitial Ag atoms, whereas in the case of In along the <0001> direction, the interstitial In was found to migrate with a higher activation energy (Ea ~ 1.78 eV) than the substitutional In (Ea ~1.42 eV). These results will be compared with first-principle calculations for understanding the energetics of defect formation and migration in both n- and p-type doping cases.

While zinc oxide is a promising material for blue and UV solid-state lighting devices, the lack of p-type doping has prevented ZnO from becoming a dominant material for optoelectronic applications. Over the past decade, numerous reports have claimed that nitrogen is a viable p-type dopant in ZnO. However, recent calculations by Lyons, Janotti, and Van de Walle [Appl. Phys. Lett. 95, 252105 (2009)] suggest that nitrogen is a deep acceptor. In our work, we performed photoluminescence (PL) measurements on bulk, single crystal ZnO grown by chemical vapor transport. Nitrogen doping was achieved by growing in ammonia. In prior work at room temperature, we observed a broad PL band at ∼1.7 eV, with an excitation threshold of ∼2.2 eV, consistent with the calculated configuration-coordinate diagram. In the present work, at liquid-helium temperatures, the PL emission increases in intensity and red-shifts by ∼0.2 eV. A peak is observed at 3.267 eV, which we tentatively attribute to an exciton bound to a nitrogen acceptor. Our experimental results indicate that nitrogen is indeed a deep acceptor and cannot be used to produce p-type ZnO.

We have investigated the photoluminescence properties of ZnO grown on sapphire substrates via the thermal oxidation of Zn-metal films at various temperatures and thicknesses. X-ray diffraction (XRD) spectra indicate that the resulting films possess a polycrystalline hexagonal wurtzite structure without preferred orientation. For films having a thickness of 200 nm, crystal grain size was observed to decrease with increasing annealing temperature up to 600ºC, and then increase at higher temperatures. Thicker films demonstrated a modest increase in grain size as temperature increased from 300ºC to 1200ºC. The influence of film thickness on the optical properties was investigated using room temperature photoluminescence (PL). Specifically, PL spectra indicate four emission bands: excitonic ultraviolet, blue, and deep-level green and yellow emission. The strongest UV emission and narrowest full width at half maximum (0.09 eV) was observed for films having a thickness of 200 nm and annealed at low temperature (300ºC). As film thickness decreased, we observed the emergence of blue emission. The emergence of blue emission when depletion width grows relative to the bulk suggests that the origin of the blue emission is related to the negatively charged Zinc interstitials found within the deletion region near the interface.

Zinc Oxide thin films were deposited on sapphire substrates by radio frequency (RF) magnetron sputtering from an ultra-high purity ZnO solid target. The ZnO films were deposited on sapphire substrates heated in oxygen and/or in vacuum prior to deposition. Additional parameters investigated included the substrate temperature varied from 25 °C to 600 °C, the deposition gas pressure varied from 5 mTorr to 40 mTorr and the gas flow rate varied from 5 to 30 standard cubic centimeter per minute (sccm). The resulting films were annealed using a rapid thermal processor in N2 gas at 900 °C for 5 min. Analyses carried out using photoluminescence spectroscopy (PL) and X-ray diffraction (XRD) measurements indicate that films deposited at 300 °C using Ar:O2 (1:1) had the best optical and microstructure qualities. Pre-heating the sapphire substrate in oxygen prior to deposition was found to create a smoother sapphire surface, and this produced a ZnO film with greatly improved qualities. This film had a luminescence peak at 3.362 eV with a full-width-half maximum (FWHM) value of 15.3 meV when measured at 11 K. The XRD 2θ-scans had peaks at 34.4° with the best FWHM value of only 0.10°. Production of high quality ZnO materials is a necessary step towards realizing highly conductive p-type doped ZnO materials which is currently a major goal in research efforts on ZnO.

Hafnium dioxide gate dielectrics, prepared by DC magnetron with low-power sputtering deposition followed by a low-temperature thermal oxidation, show greatly improved interfacial and electrical properties. Ellipsometry and X-ray photoelectron spectroscopy (XPS) measurements show a good stoichiometric HfO2 thin films with a refractive index of 1.9 and an Hf:O ratio of 1:2. The results obtained after analysis, quantification and calculation through XPS depth profile method, angle resolved XPS and interface modeling by XPS data processing software suggest a development of a complex three layer dielectric stack, including hafnium dioxide layer, a narrow interface of hafnium silicate and broad region of oxygen diffusion into silicon wafer. The measured dielectric constant of the HfO2 was about 22. The film band-gap was found to be ∼ 5.2 eV.

ZnO bulk crystals can be grown by several methods. 1) From the gas phase, usually by chemical vapor transport. Such CVT crystals may have high chemical purity, as the growth is performed without contact to foreign material. The crystallographic quality is often very high (free growth). 2) From melt fluxes such as alkaline hydroxides or other oxides (MoO3, V2O5, P2O5, PbO) and salts (PbCl2, PbF2). Melt fluxes offer the possibility to grow bulk ZnO under mild conditions (<1000°C, atmospheric pressure), but the crystals always contain traces of solvent. The limited purity is a severe drawback, especially for electronic applications. 3) From hydrothermal fluxes, usually alkaline (KOH, LiOH) aqueous solutions beyond the critical point. Due to the amphoteric character of ZnO, the supercritical bases can dissolve it up to several per cent of mass. The technical requirements for this growth technology are generally hard, but this did not hinder its development as the basic technique for the growth of α-quartz, and meanwhile also of zinc oxide, during the last decades. 4) From pure melts, which is the preferred technology for numerous substances applied whenever possible, e.g. for the growth of silicon, gallium arsenide, sapphire, YAG. The benefits of melt growth are (i) the high growth rate and (ii) the absence of solvent related impurities. In the case of ZnO, however, it is difficult to find container materials that are compatible from the thermal (fusion point Tf = 1975°C) and chemical (required oxygen partial pressure) point of view. Either cold crucible (skull melting) or Bridgman (with reactive atmosphere) techniques were shown to overcome the problems that are inherent to melt growth. Reactive atmospheres allow to grow not only bulk ZnO single crystals, but also other TCOs such as β-Ga2O3 and In2O3.

Electronic structure calculations using the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional are presented for NO-pair complexes with and without hydrogen to test the hypothesis that such defect complexes could lead to shallower levels than for isolated NO and hence p-type doping. The H is found to bind strongly to one of the N in the pair and removes thecorresponding defect level from the gap but the second N’s polaronic defect level in the gap remains deep.

Emerging NVM devices have been extensively studied as candidates to extend density scaling and power reduction beyond Si-based flash. Recently, resistive-random-access-memory (ReRAM) devices in the form of metal-insulator-metal (MIM) structures have attracted substantial attention due to their potential scalability, low power operation, and high speed. HfO2 is attractive compared to other transition metal oxides from the vantage point of CMOS process compatibility. Here, we investigate doped HfO2 with a Pt top electrode on an n+-Si substrate. By doping HfO2 with Hf or Au, improved resistive switching properties have been demonstrated in terms of enhanced cycling endurance and lower switching voltages for SET and RESET. The improvements were attributed to doping-induced oxygen vacancies. In addition, Cu-doped HfO2 devices have exhibited multilevel resistive switching.