We explore the interrelationships between the green 510 nm emission, the free‐carrier concentration, and the paramagnetic oxygen‐vacancy density in commercial ZnO phosphors by combining photoluminescence, optical‐absorption, and electron‐paramagnetic‐resonance spectroscopies. We find that the green emission intensity is strongly influenced by free‐carrier depletion at the particle surface, particularly for small particles and/or low doping. Our data suggest that the singly ionized oxygen vacancy is responsible for the green emission in ZnO; this emission results from the recombination of a photogenerated hole with the singly ionized charge state of this defect.

Mechanisms behind green photoluminescence in ZnO phosphor powders

Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.

Oxide Semiconductor Thin‐Film Transistors: A Review of Recent Advances

Solar cells based on organometallic halide perovskite absorber layers are emerging as a high-performance photovoltaic technology. Using highly sensitive photothermal deflection and photocurrent spectroscopy, we measure the absorption spectrum of CH3NH3PbI3 perovskite thin films at room temperature. We find a high absorption coefficient with particularly sharp onset. Below the bandgap, the absorption is exponential over more than four decades with an Urbach energy as small as 15 meV, which suggests a well-ordered microstructure. No deep states are found down to the detection limit of ∼1 cm–1. These results confirm the excellent electronic properties of perovskite thin films, enabling the very high open-circuit voltages reported for perovskite solar cells. Following intentional moisture ingress, we find that the absorption at photon energies below 2.4 eV is strongly reduced, pointing to a compositional change of the material.

Organometallic Halide Perovskites: Sharp Optical Absorption Edge and Its Relation to Photovoltaic Performance

Numerous candidates attempting to replace Si-based flash memory have failed for a variety of reasons over the years. Oxide-based resistance memory and the related memristor have succeeded in surpassing the specifications for a number of device requirements. However, a material or device structure that satisfies high-density, switching-speed, endurance, retention and most importantly power-consumption criteria has yet to be announced. In this work we demonstrate a TaO(x)-based asymmetric passive switching device with which we were able to localize resistance switching and satisfy all aforementioned requirements. In particular, the reduction of switching current drastically reduces power consumption and results in extreme cycling endurances of over 10(12). Along with the 10 ns switching times, this allows for possible applications to the working-memory space as well. Furthermore, by combining two such devices each with an intrinsic Schottky barrier we eliminate any need for a discrete transistor or diode in solving issues of stray leakage current paths in high-density crossbar arrays.

A fast, high-endurance and scalable non-volatile memory device made from asymmetric Ta2O5−x/TaO2−x bilayer structures

Graphene has been hailed as a wonderful material in electronics, and recently, it is the rising star in photonics, as well. The wonderful optical properties of graphene afford multiple functions of signal emitting, transmitting, modulating, and detection to be realized in one material. In this paper, the latest progress in graphene photonics, plasmonics, and broadband optoelectronic devices is reviewed. Particular emphasis is placed on the ability to integrate graphene photonics onto the silicon platform to afford broadband operation in light routing and amplification, which involves components like polarizer, modulator, and photodetector. Other functions like saturable absorber and optical limiter are also reviewed.

Graphene photonics, plasmonics, and broadband optoelectronic devices.

The results of optical-absorption measurements determined by photothermal deflection spectroscopy, primary photoconductivity, and secondary photoconductivity on undoped and phosphorus-doped hydrogenated amorphous silicon films (a-Si:H) are reported. A normalization procedure for obtaining photocurrent spectra at constant generation rate is demonstrated. From these measurements, the efficiency-mobility-lifetime product (eta..mu..tau) for electrons is found to be constant from 2.0 to approx.0.9 eV for both undoped and phosphorus-doped a-Si:H. For excitations less than approx.0.9 eV, there is evidence that the product eta..mu..tau for electrons drops rapidly; similarly, the eta..mu..tau for holes exhibits a rapid decrease in undoped material for photon energies less than approx.1.5 eV. A model is proposed to explain the results, resolving a discrepancy between secondary- and primary-photoconductivity measurements of the optical absorption.

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Energy dependence of the carrier mobility-lifetime product in hydrogenated amorphous silicon

Light-induced defect creation is demonstrated in hydrogenated polycrystalline silicon (poly-Si:H). The newly created defects are metastable as in hydrogenated amorphous silicon (a-Si:H). However, unlike a-Si:H the magnitude of the light-induced degradation decreases with repeated illumination and anneal cycles and is restored upon reexposure to monatomic hydrogen. This unique response arises from the inherent structural inhomogeneity of the polycrystalline material and establishes that hydrogen directly contributes to the metastability in poly-Si:H.

Light-induced creation of metastable paramagnetic defects in hydrogenated polycrystalline silicon.

A method is described for determining the spatial profiles of electron traps in dielectric thin films. The method is an extension of avalanche injection and charge centroid measurements. By determining the change in the charge centroid and the injected charge after a sequential series of pulses, the densities of electron traps as a function of depth in both low‐pressure‐chemical vapor deposited (LPCVD) and plasma‐enhanced‐chemical vapor deposited (PECVD) silicon nitrides were determined. Contrary to previous assumptions of a uniform trap density in the nitride, both nitrides exhibit interface trap densities extending 10–15 nm into the film that is between 6 and 15 times larger than the bulk trap density of 0.5–2×1018 cm−3. The trap capture cross section was determined to be 6–10×10−13 cm2. The interface trap density of commercial LPCVD nitride deposited at higher temperature was higher than that found for PECVD nitride. The spatial resolution and limitations of the profiling technique, avalanche injection...

Spatial profiling of electron traps in silicon nitride thin films

Using first-principles calculations, we demonstrate an explicit reaction pathway for carrier-induced changes in hydrogenated Si through dissociation of paired-H complexes. The complex dissociates through the capture of charge carriers with calculated kinetic barriers for electron- and hole-induced dissociations of 1.1 and 0.9 eV, respectively, in crystalline Si, in general agreement with the experimentally observed activation energies for single-carrier defect creation in hydrogenated a-Si. Exciton lowering of the barrier accounts for the low activation energy of light-induced defect formation.

Diatomic-hydrogen-complex dissociation: A microscopic model for metastable defect generation in Si

A method of marking employs a marking apparatus in which a propellant stream is passed through a channel and directed toward a substrate. Marking material, such as ink, toner, etc., is controllably introduced into the propellant stream and imparted with sufficient kinetic energy thereby to be made incident upon a substrate. At sufficient velocity, and with appropriate marking material, the marking material may be kinetically fused to the substrate. A multiplicity of channels for directing the propellant and marking material allow for high throughput, high resolution marking. Multiple marking materials may be introduced into the channel and mixed therein prior to being made incident on the substrate, or mixed or superimposed on the substrate without registration. One example is single-pass, full-color printing.

Warren B. Jackson

Papers

Energy dependence of the carrier mobility-lifetime product in hydrogenated amorphous silicon

Light-induced creation of metastable paramagnetic defects in hydrogenated polycrystalline silicon.

Spatial profiling of electron traps in silicon nitride thin films

Diatomic-hydrogen-complex dissociation: A microscopic model for metastable defect generation in Si

Method of treating a substrate employing a ballistic aerosol marking apparatus