Transparent conductive electrodes are an important part of LCD displays, solar cells, and lightemitting diodes, but a replacement must be found for indium tin oxide (ITO), which has become very expensive. One of the prime candidates is ZnO doped with Al, Ga, or In. Here we present a convenient analytical mobility model that yields donor N_D and acceptor N_A concentrations from Hall-effect measurements at a single temperature, including room temperature (RT). This model includes scattering from phonons and boundary imperfections as well as from ionized impurities and point defects. We apply it to films grown by pulsed laser deposition at 200 °C in 10 mTorr of pure Ar. For a film of thickness 275 nm, the Hall-effect measurements yield a RT resistivity ρ = 1.9 x 10^-4 Ω-cm, mobility μ = 28 cm²/V-s, and carrier concentration n = 1.1 x 10²¹ cm^-3, and the mobility model gives N_D = 1.6 x 10²¹ cm^-3 and N_A = 4.9 x 10²⁰ cm^-3. Also, the transmittance is above 90% in the visible range. Annealing in forming gas gives ρ = 1.5 x 10^-4 Ω-cm, mobility μ = 42 cm²/V-s, carrier concentration n = 1.0 x 1021 cm-3, ND = 1.1 x 1021 cm-3 and N_A = 1.0 x 1020 cm^-3. If the compensation ratio K = NA/ND can be maintained at about 0.1, and N_D increased to about 3 x 1021 cm^-3, then the model predicts a RT resistivity of less than 7 x 10^-5 Ω-cm, well below present ITO values.

ZnO (002) films of thickness 0.5 μm were grown on c-plane sapphire substrates by Pulsed Laser Deposition technique at 400°C in oxygen ambient of 75 mTorr and implanted with 8x10¹⁴ cm^-2 dose of phosphorus ions of energy 50 keV (Sample A) followed by Rapid Thermal Annealing in Ar (Sample B) and oxygen atmospheres (Sample C) at 750°C (30 seconds). AFM images depicted root-mean-square roughness for Sample A (10.072 nm), B (9.314 nm) and C (4.9 nm). Room-temperature Hall study revealed n-type conductivity with carrier concentrations of 9.69x10¹⁹cm^-3, 1.36x10²⁰ cm^-3, 4x10¹⁸ cm^-3 and Hall mobility of 0.727 cm²/V-s, 12.44 cm²/V-s, 54.3 cm²/V-s for Sample A, B and C respectively. Possible reasons might be the formation of vacancy clusters by implantation for Sample A, production of oxygen vacancies with agglomeration of vacancy clusters and without further aggregation of vacancy clusters with higher annealing temperature for Sample B and C respectively. Dominance of donor-bound exciton peaks were found to be at 3.295 eV, 3.284 eV, 3.281 eV and 3.272 eV for unimplanted sample, Sample A, B and C respectively from roomtemperature photoluminescence study.

We fabricate various ZnO (zinc oxide) nanostructures, such as nanorods, nanotips and nanoflowers, as well as ZnO subwavelength grating structures for applications in optoelectronic devices such as solar cells, light emitting diodes, and biosensors. The optical properties are theoretically analyzed using the rigorous coupled-wave analysis method. The fabricated ZnO nanostructures are of wurzite crystal structure. The reflection and absorption characteristics depend strongly on the shape and geometry of Zn nanostructures. The ZnO nanostructures with Au (or Ag) particles, based on surface plasmons, are also investigated.

Zinc oxide (ZnO) and especially in the nanostructure form is currently being intensively investigated world wide for the possibility of developing different new photonic devices. We will here present our recent findings on the controlled low temperature chemical growth of ZnO nanorods (NRs) on different large area substrates. Many different heterojunctions of ZnO NRs and p-substrates including those of crystalline e.g. p-GaN, p-SiC or amorphous nature e.g. p-polymer coated plastic and p-polymer coated paper will be shown. Moreover, the effect of the p-electrode of these heterojunctions on tuning the emitted wavelength and changing the light quality will be discussed. An example using ZnO NR/p-GaN will be shown and the electrical and electro-optical characteristics will be analyzed. For these heterojunctions the effect of post growth annealing and its effect on the electroluminescence (EL) spectrum will be shown. Finally, intrinsic white light emitting diodes based on ZnO NRs on foldable and disposable amorphous substrates (plastic and paper) will also be presented.

We investigated the influence of the growth method, growth conditions, and post-growth treatments on the ZnO nanorod properties and the performance of heterojunction light emitting diodes (LEDs) based on ZnO nanorods. Due to small lattice mismatch between GaN and ZnO, we will mainly consider p-GaN/n-ZnO nanorod heterojunctions. The influence of p-GaN substrate and the influence of growth method and growth conditions used for ZnO nanorods on the LED performance will be discussed.

We have been succeeded in growing vertically aligned ZnO nanowires by a newly developed nanoparticle-assisted pulsed-laser deposition (NAPLD) without any catalyst. In this study, layer structured ZnO nanowires, such as film-wire layered structure and core/shell structure, were synthesized using multi-target changer system. In this paper, synthesis and photoluminescence characteristic of the layer structured ZnO nanowires are described.

A single-step bridging method is used to fabricate bridged wide bandgap semiconductor nanowire structures as ultraviolet photodetectors. The nanowires are bridged across self-grown electrodes in a chemical vapor deposition process without resorting to epitaxial growth and photolithography techniques. Depending on the surface depletion properties of the nanowires, two types of bridged nanowire structures are designed. For ZnO nanowires with strong surface depletion effect, a bascule nanobridge structure is adopted. For β-Ga2O3 nanowires with weak surface depletion effect, a direct nanobridge structure is used. The bridged nanowire photodetectors are operated with a few volts and show good spectral selectivity, and high and fast photoresponse.

Using zinc oxide (ZnO) nanostructures, nanorods (NRs) and nanoparticles (NPs) grown on different substrates (sub-micrometer glass pipettes, thin silver wire and on plastic substrate) different bio-sensors were demonstrated. The demonstrated sensors are based on potentiometric approach and are sensitive to the ionic metals and biological analyte in question. For each case a selective membrane or enzyme was used. The measurements were performed for intracellular environment as well as in some cases (cholesterol and uric acid). The selectivity in each case is tuned according to the element to be sensed. Moreover we also developed photodynamic therapy approach based on the use of ZnO NRs and NPs. Necrosis/apoptosis was possible to achieve for different types of cancerous cell. The results indicate that the ZnO with its UV and white band emissions is beneficial to photodynamic therapy technology.

ZnO is a superior multifunctional material with broad applications in electronics, optoelectronics, and piezoelectric transducers. The nanowire (NW) morphology is an ideal system for studying transport process in one-dimensionally (1D) confined objects and developing new generation nanodevices with high performance. This paper will review we will review the self-catalyzed growth of ZnO nanostructures. An interesting cluster drifting phenomenon was discovered, which evidenced this growth mechanism and provide a control toward the morphology. In addition, a strainversus- dislocation (SVD) model will be discussed to explain the growth of vertically aligned ZnO nanostructures on heterogeneous substrates. Finally, a novel application of using the piezoelectric ZnO NWs for converting nano-scale mechanical energy into electric energy is presented.

A first-principles study has been performed to evaluate the electronic and magnetic properties of the Zn_1-xMn_xO₁-_yN_y system. Doping Mn atoms introduces local magnetic moments, while doping N atoms introduces carriers. It is worth noting that intrinsic Mn-doped ZnO favors antiferromagnetic (AFM) ordering, and this cannot be changed by raising Mn ions concentration continuously. However, by the codoping N and Mn, it is possible to change the ground state from no-metallic AFM to half-metallic ferromagnetic (FM) and make ZnO as a dilute magnetic semiconductor. We have succeeded in describing the change (from AFM to FM) by using the magnetic interaction that is hole-mediated FM due to the hybridization between N 2p and Mn 3d states. Furthermore, the most stable configurations are found to be -O-Mn-N-Mn-O-.Our results are in good agreement with other theoretical results that are additional holes carriers is one of the possible mechanisms.

In order to develop efficient visible upconversion lasers and optical fiber amplifiers, the detailed spectroscopic properties of singly doped Er³⁺ and codoped Er³⁺-Yb³⁺ ions in lead tungsten tellurite (LTT) glasses have been investigated. The glasses were prepared by the conventional melt quenching technique. Absorption, visible upconversion spectra and NIR emission spectra were recorded as a function of Yb³⁺ ions concentrations. Judd-Ofelt (J-O) analysis has been performed for the spectral intensities of Er³⁺and Er³⁺-Yb³⁺ absorption bands. Spontaneous emission probabilities (A_R), radiative lifetimes (τ_R) and branching ratios (β_R) were calculated by using the phenomenological Judd-Ofelt intensity parameters. Three strong upconversion emission bands centered at 526, 551 and 665 nm were observed under 980nm excitation, due to the energy transfer process from Yb³⁺ to Er³⁺ ions. The green emissions centered at 526 and 551 nm and the red emission at 665 nm are attributed to ²H_11/2→ ⁴I_15/2, ⁴S_3/2→ ⁴I_15/2 and ⁴F_11/2→ ⁴I_15/2 transitions of Er³⁺ions respectively. The relative intensity variations of ²H_11/2→ ⁴I_15/2, ⁴S_3/2→ ⁴I_15/2 and ⁴F_9/2→ ⁴I_15/2 transitions have been explained on the basis of the increase in the population accumulation rates of ²H_11/2 ,⁴F_9/2 and ⁴S_3/2 levels. The peak stimulated emission cross-section (σe) and gain bandwidth parameter (σe×▵λ_eff) of ⁴I_13/2 → ⁴I_15/2 transition at 1.54 μm for Er³⁺ and Er³⁺-Yb³⁺ ions in LTT glasses have been determined and compared with different glass hosts. The stimulated emission cross-sections (σ_e) determined by using McCumber theory for the ⁴I_13/2 → ⁴I_15/2 transition are compared with the measured (σ_e) values obtained from the emission data. The results of these investigations revealed that the lead tungsten tellurite (LTT) glasses could be more useful as promising host materials for the design and development of optical fiber amplifiers and upconversion lasers.

We have previously discovered a novel, facile approach to encapsulate ZnO nanorods within thiol complexes. This approach results in a thiol uptake of 30-40% and a 400-500 nm thick thiol-Zn-thiol complex encapsulation layer surrounding ZnO nanorods. By controlling experimental parameters, it is possible to control the thiol deposition, enabling less uptake, which results in a surface monolayer instead of encapsulation. Through this approach, thiol modification of other metal oxide materials, namely TiO₂, Al₂O₃, and MgO, has been attempted. FTIR analysis indicates that thiol adsorption occurs only on ZnO; chemisorption of thiols on other nanoparticles is not evident. Ultrahigh vacuum single crystal adsorption studies demonstrate that ZnO(0001) is also more susceptible to thiol monolayer formation, as evidenced by lack of methanethiol adsorption on TiO₂(110) and MgO(0001). These results indicate that the facile thiol modification approach opens a new avenue for surface modification of multi-component metal oxide materials by enabling selective thiol modification of ZnO. This work has potential applicability for creating multiple ligand-functionalized materials, which could be useful for the design of novel multiplexing sensors and photovoltaics.

X-ray scattering methods were applied to the study of thin mosaic ZnO layers deposited by Pulsed Laser Deposition on c-Al₂O₃ substrates and thin mosaic GaP layers deposited by Molecular Beam Epitaxy (MBE) on Si(001) substrates. For both systems, High Resolution (HR) studies revealed two components in the ω scans (transverse scans) which were not resolved in conventional "open-detector" ω rocking curves: a narrow, resolution-limited, peak, characteristic of longrange correlation, and a broad peak, due to defect-related diffuse-scattering giving a limited transverse structural correlation length. Thus, for such mosaic films, the conventional ω rocking curve Full Width at Half Maximum linewidth was found to be inadapted as an overall figure-of-merit for the structural quality, in that, first, the different contributions were not meaningfully represented, and, second, the linewidth depends more strongly on the film thickness than on the dispersion in the crystallographic orientation or the defect density. A "Williamson-Hall like" integral breadth (IB) metric for the HR (00.l) transverse-scans was developed as a reliable, fast, accurate and robust alternative to the rocking curve linewidth for routine non-destructive testing of such mosaic thin films. For ZnO/c-Al₂O₃ films of various thicknesses, it was deduced from the transverse scans profiles that this finite lateral correlation length may arise from misfit dislocations which accommodate the lattice-mismatch at the film-substrate interface. This WHL method is shown to be a generic approach applicable to the study of other mosaic, epitaxial, thin-film systems as illustrated through the study of mosaic GaP thin films grown by MBE on Si(001) 4°-off substrates. For this heterogeneous system, it was found from the transverse scan profiles around (002) and (006) that anti-phase crystalline domains can be evidenced. A finite correlation length associated with lateral anti-phase domain size was proposed.

First-principles calculations are used to study the properties of LiGaO₂, a potentially useful opto-electronic material in conjunction with ZnO. Its band structure is evaluated using the quasiparticle self-consistent GW method. The band gap is found to be significantly larger than the reported room temperature absorption onset. Estimates are made of the finite temperature and excitonic corrections. Potential n- and p-type dopants are studied in the local density approximation, using a supercell approach. The lattice dynamical properties are studied using the density functional perturbation method.

The radiation damage formation upon low temperature ion implantation and neutron irradiation has been compared for GaN and ZnO. Both materials exhibit strong dynamic annealing effects during implantation, even at 15 K, leading to high amorphisation thresholds. The damage build-up with fluence was found to proceed in a similar way for GaN and ZnO, both showing two saturation regimes below the amorphisation level where, over wide fluence regions, the damage level increases only very slowly. For low fluences the damage accumulation rate is similar for both materials. For higher fluences, on the other hand, GaN shows considerably higher damage levels and finally collapses into an amorphous structure while ZnO remains single crystalline up to the highest fluence of 7×10¹⁶ Ar/cm². Neutron irradiation produces similar defects as ion implantation but within the entire sample while the defect density is much lower. The main effect of irradiation on the structural properties of GaN is an expansion of the c-lattice parameter. Optical properties are significantly deteriorated after irradiation and only recover partially after annealing. ZnO does not suffer such a pronounced change of the lattice parameters but reveals a strong deterioration of the surface, possibly due to blistering and exfoliation. At the same time the optical properties are less affected than for GaN. The near band edge emission is partly quenched but recovers to a large extend after annealing while broad defect bands are observed below the bandgap for irradiated samples, before and after annealing.

Today there is a strong interest in the scientific and industrial community concerning the use of biopolymers for electronic applications, mainly driven by low-cost and disposable applications. Adding to this interest, we must recognize the importance of the wireless auto sustained and low energy consumption electronics dream. This dream can be fulfilled by cellulose paper, the lightest and the cheapest known substrate material, as well as the Earth's major biopolymer and of tremendous global economic importance. The recent developments of oxide thin film transistors and in particular the production of paper transistors at room temperature had contributed, as a first step, for the development of disposable, low cost and flexible electronic devices. To fulfil the wireless demand, it is necessary to prove the concept of self powered devices. In the case of paper electronics, this implies demonstrating the idea of self regenerated thin film paper batteries and its integration with other electronic components. Here we demonstrate this possibility by actuating the gate of paper transistors by paper batteries. We found that when a sheet of cellulose paper is covered in both faces with thin layers of opposite electrochemical potential materials, a voltage appears between both electrodes -paper battery, which is also self-regenerated. The value of the potential depends upon the materials used for anode and cathode. An open circuit voltage of 0.5V and a short-circuit current density of 1μA/cm² were obtained in the simplest structure produced (Cu/paper/Al). For actuating the gate of the paper transistor, seven paper batteries were integrated in the same substrate in series, supplying a voltage of 3.4V. This allows proper ON/OFF control of the paper transistor. Apart from that transparent conductive oxides can be also used as cathode/anode materials allowing so the production of thin film batteries with transparent electrodes compatible with flexible, invisible, self powered and wireless electronics.

We briefly review principles and main features of an electric double layer transistor (EDLT) as well as electric field induced superconductivity in SrTiO₃. EDLT is a field-effect transistor that employs an electrolyte as a gate dielectric. An electric double layer between a semiconductor and the electrolyte attains much higher breakdown field than the maximum of a solid gate dielectric, resulting in high density charge accumulation up to 10¹⁴cm^-2. That density is sufficient for inducing new physical phases, such as superconductivity and ferromagnetism, on various oxide systems. We employed a surface of a SrTiO₃ single crystal as a semiconductor channel. We have demonstrated insulator-tosuperconductor transition by electric field-effect without chemical doping. Charge carrier density was linearly increased from zero to 10¹⁴ cm^-2 with increasing gate bias to 3.5 V. Superconducting critical parameters, such as critical temperature T_c, critical magnetic field H_c, and critical current density J_c were examined as a function of carrier density by varying gate bias. T_c was almost constant as a function of the carrier density, contrasting to bell-shaped dependence of H_c and J_c. Temperature dependence of I-V curve shows the BKT-type transition, which indicates two-dimensional superconductivity in the electric field induced superconductivity.

As a stepping point to predicting band gaps and electronic structure of more complicated materials based on alkaline and post-transition metal oxides, we examine the valence structure of these simple binary oxides using both high resolution X-ray emission spectroscopy and a variety of density functional theory calculations. We confirm that the new modified Becke-Johnson (mBJ) extension of the Perdew-Burke-Ernzerhoff (PBE96) functional provides a good estimate of the band gaps of these materials, but we demonstrate that it does not provide an accurate depiction of the valence structure in post-transition metal oxides. A calculation with an exact Hartree-Fock exchange energy does a better job of calculating the valence structure, but no longer accurately reproduces the band gap. Since we expect that d-p repulsion may play an important role in shaping the band gap, we suggest that combining the valence structure from the latter calculation with the band gap of the former calculation may be the best approach for predicting the electronic structure of more advanced materials based on these post-transition metal oxides precursors.

Cross-sectional scanning tunneling microscopy (XSTM) is developed for studying the interfaces of the complex oxide heterostructures. Since most of the complex oxide materials have a perovskite structure, which does not have cleavage plane, it posed an experimental challenge for utilizing STM on the fractured surfaces. A well-controlled method for fracturing non-cleavable materials was developed by using the common subtrate: Nb-doped SrTiO₃ (Nb:STO). Through systematically studies on the control of the fracturing conditions, on the tip-sample interactions and on the resulting fractured surfaces of Nb:STO, atomic flat terraces are routinely created and stable measurements are achieved. By harnessing the well-controlled fracturing method and the well-controlled tip conditions to a thin film system, La_2/3Ca_1/3MnO₃/Nb:STO (LCMO/Nb:STO), XSTM as well as the ability of cross-sectional scanning tunneling spectroscopy (XSTS) directly revealed the band diagram mapping across the interface. The novel developed, well-controlled XSTM/S for the interfaces of complex oxide heterostructures opened a door for accurate determination of local electronic properties across and at the interface.

A diode with Sb-doped p-type ZnO, MgZnO/ZnO/MgZnO double heterojunction, and undoped n-type ZnO layers was grown on c-plane sapphire substrate by plasma-assisted molecular-beam epitaxy. Hall effect measurement showed that the top p-type Sb-doped ZnO layer has a hole concentration of 1×1017cm-3. Mesa geometry light emitting diodes were fabricated with Au/Ni and Au/Ti Ohmic contacts on top of the p-type and n-type layers, respectively. Strong ultraviolet emission was achieved, which yielded an output power of 457 nW at 140 mA. The drastic enhancement of the output power is attributed to carrier confinement in the good-quality intrinsic layer of the double heterojunction. The spatial distribution of light emission was characterized.

In the last decades, development of the (Al,Ga,In)N materials has led to new generations of opto- and micro-electronic devices. More recently, novel B(Al,Ga,In)N alloys have been proposed for optical applications in the UV range. Since material containing boron possesses unique properties, the B(Al,Ga,In)N materials system is expected to permit the design of improved and/or novel devices. To evaluate this potential, an improved knowledge of the physical properties of these new materials will be required, however. In this work, investigation of optical, structural, and compositional properties of low-boron content BGaN and BAlN ternary and BInGaN quaternary materials grown through Metalorganic Vapor Phase Epitaxy (MOVPE) are presented. It is shown that inclusion of a small amount of boron strongly affects the optical properties allowing the fabrication of BGaN-based Distributed Bragg Reflectors (DBRs) or Distributed Bragg Confinement layers (DBCs) with large refractive index contrast. Indeed, 1% of boron in BGaN/GaN multilayer structures gives a refractive index contrast of more than 0.1, which is equivalent to that of AlGaN/GaN containing 22% aluminum. The potential of boron-based material technology is illustrated for visible range solar cells applications through the example of BInGaN with good crystalline quality grown on ZnO buffered silicon substrates. It was found that through boron introduction, reduced lattice mismatch, and thus reduced tensile strain, could be obtained for high In contents.

E-O Sensors are being developed for a variety of Military Systems Applications. These include UV, Visible, SWIR, MWIR and LWIR Nano Sensors. In this paper, we will discuss growth and characterization of ZnO Nanowires on a variety of substrates that include Silicon, ZnO and flexible substrates. The critical technologies being developed include ZnO nanostructures with wide band gap for UV detection for a variety of threat warning applications. We will present experimental results on the structural, electrical and optical properties of ZnO nanowire for UV detectors. Experimental results on ZnO based nanostructures demonstrate enhanced UV sensitivity and path forward for larger arrays.

The LIFT experiments were performed in air at room temperature for ITO films with the thickness of 180nm. A line pattern of the ITO film was obtained using a second harmonic generation SHG (532nm) beam of a Q-switched Nd:YAG laser (5.18W) with the repetition rate of 40kHz and the pulse width of 13ns. The beam was scanned using a galvano mirror optical setup system. Two kinds of sandwiched glass plate samples were used: (1) a glass plate deposited with ITO film (donor) is contact with another glass substrate (receiver) with no-gap, that is, the ITO film is in direct contact with a receiver glass, and (2) the donor is placed against the receiver glass with an 0.14mm air gap using a glass spacer. These samples were irradiated by the scanned beam with different scanning speeds. LIFT-transferred film pattern with the linear array of dot prints was obtained for the scanning speed of 200cm/s, but for the scanning speed of 10cm/s, the linear array of continuous printed tracks was produced. The edge of the printed track was clearer in (2) than (1) for the scanning speed of 10cm/s. As a result, the sample of type (2) with air-gap is preferable to obtain the line printed pattern with clear track edge, and the scanning speed should be smaller than 10 cm/s for this laser.

We have succeeded in layer-by-layer epitaxial growth of MgO (111) films using single-crystalline NiO buffer films by pulsed laser deposition along the [111] polar growth direction despite a strong electrostatic instability. Layer-by-layer growth was clearly observed up to ~ 10 MgO layers with monolayer step and terrace structure. Further thicker films of 10 - 500 MgO layer present the root mean square surface roughness as small as ~ 0.2 nm with high crystalline quality comparable to the single-crystal NiO buffer layers although the step and terrace structure disappeared. Transmission electron microscopy study indicates formation of an atomic smooth MgO/NiO interface although low-quality domains with dislocations and strains and high-quality domains coexisted in the regin away from the interface. Thus the electrostatic instability of thicker MgO films induced the switching from layer-by-layer to three dimensional growth mode by introducing the double domain structures.

Nano particles exhibit physical and chemical properties distinctively different from that of bulk due to high number of surface atoms, surface energy and surface area to volume ratio. Laser is a unique source of radiation and has been applied in the synthesis of nano structured metal oxides. The pulsed laser ablation (PLA) technique in liquid medium has been proven an effective and simple technique for preparing nanoparticles of high purity. Pulsed laser deposition (PLD) is another way to fabricate nano structured single crystal thin films of metal oxides. PLA technique has been applied in our laboratory for the growth of metal oxides such as nano-ZnO, nano-ZnO₂ nano- SnO₂, nano-Bi₂O₃, nano-NiO and nano-MnO₂. Different techniques such as AFM, UV, FT-IR, PL and XRD were applied to characterize these materials. We will present our latest development in the growth of nano metal oxides using PLA and PLD.

The applicability of anti-resonant reflecting optical waveguides fabricated on silicon substrates has been demonstrated for different optical devices and sensors. In particular, it has been shown that in order to have virtual single-mode operation in ARROWs, smaller constraints are imposed in the thickness and refractive index of the constituent layers than in the case of Total Internal Reflection waveguides. On the other hand, if rib ARROWs are fabricated through Reactive Ion Etching (RIE), high sidewall roughness is observed if metallic mask is used, which leads to undesirable losses. This can be improved if the RIE step is done in the lower layers, leading to rounder but smoother core sidewalls. In this work we present an alternative method for achieving the lateral confinement in ARROW waveguides fabricated with silicon technology. This method consists in doing the RIE step before the core definition so as to have the lower cladding layer and part of the silicon substrate etched away. Pedestal hollow core ARROWs have been proposed and fabricated but in the case of conventional ARROW waveguides this has not been done, to our best knowledge. Simulations results regarding propagation losses are presented for different rib heights and widths and compared to experimental results.

Self-assembled composite nanostructures integrate various basic nano-elements such as nanoparticles, nanofilms and nanowires toward realizing multifunctional characteristics, which promises an important route with potentially high reward for the fast evolving nanoscience and nanotechnology. A broad array of hierarchical metal oxide based nanostructures have been designed and fabricated in our research group, involving semiconductor metal oxides, ternary functional oxides such as perovskites and spinels and quaternary dielectric hydroxyl metal oxides with diverse applications in efficient energy harvesting/saving/utilization, environmental protection/control, chemical sensing and thus impacting major grand challenges in the area of materials and nanotechnology. Two of our latest research activities have been highlighted specifically in semiconductor oxide alloy nanowires and metal oxide/perovskite composite nanowires, which could impact the application sectors in ultraviolet/blue lighting, visible solar absorption, vehicle and industry emission control, chemical sensing and control for vehicle combustors and power plants.

ZnO has been a subject of intense research in the optoelectronics community owing to its wide bandgap (3.3eV) and large exciton binding energy (60meV). However, difficulty in doping it p-type posts a hindrance in fabricating ZnObased devices. In an attempt to make it p-type we have studied Li-implanted (Energy=40keV, dose=5x10¹³cm^-2) <002> ZnO films grown over <001> sapphire substrates by Pulsed Laser Deposition technique at 400°C (sample A). The samples were subsequently subjected to Rapid Thermal Annealing at 650° and 750°C (samples B and C) for 30 seconds. Room temperature Photoluminescence study of as-deposited sample reveal consistent Donor-bound exciton (D⁰X) peak at 3.3eV, which shifts to 3.298eV, 3.298eV, and 3.289eV for samples A, B and C respectively. This data validates the n-type conductivity of the samples with a carrier concentration and Hall mobility of 8.68x10¹⁹cm^-3, 1.13x10¹⁹cm^-3 and 2.9x10²⁰cm^-3 and 2.14cm²/V-sec, 35.2cm²/V-sec, 16.9cm²/V-sec for samples A, B and C respectively. The reduced energy of D⁰X peak is probably due to strain variations occurred during the various processing steps. While the higher carrier concentration in sample C can be attributed to aggregated vacancy clusters at high temperature annealing. Since Li acts as an acceptor for ZnO, so a free electron-acceptor (FA) peak at 3.227eV, 3.217eV and 3.225eV in samples A, B and C is evident. A third peak at 3.128eV may be due to the donor-acceptor pair, a reason for a lower energy FA peak for sample B.

We present a fabrication procedure for ZnO channel waveguides intended for nonlinear optical applications. Ar ion milling was used to etch the single crystal thin film samples, and the effects of bias power, chamber pressure and Ar flow rate were investigated, finding optimal parameters for waveguide fabrication. The effect of sidewall roughness was estimated by comparing the results of cut-back measurements and an analytical model. We show an easy and effective method for the fabrication of ZnO channel waveguides.

We investigated a possibility of making rutile TiO₂ channel waveguides for nonlinear optical applications. Single mode conditions, the group velocity dispersion and the nonlinear-optical parameters for the rutile TiO₂ channel waveguides were calculated using the finite-element method. We also fabricate channel waveguides with rutile TiO₂ using reactive ion etching. The propagation loss measured by the cut-back method was around 6 dB/mm. According to our simulation, around 70 nm of spectral broadening owing to the self-phase modulation will be expected by a pumping optical pulse with 360 W peak power.

Calcium fluoroborate (CFB) glasses doped with different concentrations of Tb³⁺ ions have been prepared with molar composition of (42-x) B₂O₃ + 20 CaF₂ +15 CaO + 15 BaO + 8 Al₂O₃ + x TbF₃ (x=0.05, 0.1, 0.5, 1.0, 2.0 and 4.0) by melt quenching method. Optical absorption spectrum for 1.0 mol% of Tb³⁺:CFB glass was recorded in UV-Vis-NIR regions. Radiative parameters such as radiative transition probabilities (A_R), radiative lifetimes (τ_R), radiative branching ratios (β_R) for the ⁵D₃ and ⁵D₄ excited states have been calculated by using the Judd-Ofelt parameters (Ω_λ=2,4,6). The luminescence spectra recorded for different concentrations of Tb³⁺ ions in CFB glasses exhibit seven and four bands originating from ⁵D₄ and ⁵D₃ excited states respectively. As the concentration of Tb³⁺ ions increases the intensities of luminescence peaks originating from ⁵D₄ state increases, whereas, the quenching of intensities has been observed for the emission peaks originating from ⁵D₃ state due to energy transfer through cross-relaxation channel (⁵D₃ : ⁷F₆) → (⁵D₄ : ⁷F₀). The experimental lifetimes of ⁵D₄ state for all the concentrations of Tb³⁺ ions are equal and exhibit single exponential decay with highest quantum efficiency which confirms that these glasses can be used for high intensity green emission even at high concentrations of Tb³⁺ ions.

In this work we propose an integration of two kinds of optical devices: an incandescent micro lamp and an interferometric filter, both fabricated on silicon technology. The micro lamp is based on a chromium micro resistor, working as a lamp filament, embedded between two oxynitride films and self-sustained through the partial silicon substrate etching using KOH solutions. The interferometric filters were fabricated through the deposition of periodically alternated PECVD Si₃N₄ and SiO₂ films whose thicknesses were previously defined by numerical simulations. We present the fabrication of these two devices separately and its integration in a hybrid way. The results demonstrated that light filtering can be obtained on micro-lamps light emission spectrums when integrated with interferometric filters, at the wavelength intervals defined by filter transmittance spectrums. Electrical characterization allowed determining the necessary current to obtain constant and stable light emission from micro lamps. The possibility of integration in a unique process, in a quasi-monolithic integration, is proposed.

Recently, there has been a surge of activity in the development of next-generation transparent thin film transistors for use in applications such as electronic paper and flexible organic light emitting diode panels. Amongst the transparent conducting oxides attracting the most interest at present are Amorphous Oxide Semiconductors (AOS) based on ZnO because they exhibit enhanced electron mobility (μ), superior capacity for processability in air and improved thermodynamic stability compared with conventional covalent amorphous semiconductors and existing AOS. Moreover, they give excellent performance when fabricated at relatively low temperature and can readily be made in large area format. Thus, they are projected to resolve the trade-off between processing temperature and device performance and thereby allow fabrication on inexpensive heatsensitive substrates. For the moment, however, an undesireable post-deposition annealing step at a temperature of about 200°C is necessary in order to obtain suitable electrical and optical properties. This paper demonstrates the possibility of directly engineering amorphous ZnO with relatively high conductiviy at room temperature on paper and mylar substrates using pulsed laser deposition.

We have investigated the optical and structural properties of polycrystalline zinc oxide (ZnO) films grown on glass and c-plane sapphire substrates. Zinc-metal films where grown on glass and sapphire substrates via dc-sputter deposition at room temperature with subsequent thermal annealing in air at 300° and 600°C. X-ray diffraction spectra indicate that after annealing, the resulting ZnO films possess a polycrystalline hexagonal wurtzite structure without a preferred orientation. Room-temperature photoluminescence (PL) spectra indicate that films annealed at 300°C exhibited the strongest ultraviolet (UV) emission intensity and lowest deep-level emission. Increasing deep-level green emission was observed with increasing annealing temperature for films grown on glass substrates, and a red shift in the excitonic UV band was observed for films grown on sapphire substrates. ZnO-based metal-semiconductor-metal (MSM) UV photodetectors where fabricated via sputter deposition of aluminum ohmic contacts on the resulting ZnO films. Decreasing photocurrent is seen for increasing annealing temperature, which is consistent with PL studies.