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.

A systematic investigation of the transport properties of PtSi on phosphorus-doped hydrogenated amorphous silicon (a-Si:H) interfaces is presented. The transition from rectifying Schottky barriers to Ohmic contacts is observed as the doping level is increased. The barrier heights of PtSi on a-Si:H versus doping concentration and applied bias are measured with use of internal photoemission. In addition, the activation energy, ideality factor, flat-band voltage, and reverse-bias current-voltage characteristics are also determined. The results are analyzed in terms of the theory for thermionic-field-emission tunneling through the barrier. The agreement indicates that tunneling is extremely important for barriers on all but the lowest-doped a-Si:H at room temperature. While a change \ensuremath{\sim}0.6 eV of the effective barrier height is observed, the analysis indicates that the actual barrier height is independent of doping despite a change in the Fermi level of \ensuremath{\sim}0.4 eV. No evidence for the lowering of the barrier due to phosphorus-induced donor levels is found. The origin of the barrier formation and evolution of the electrical characteristics of the contact as a function of doping are discussed.

Schottky barriers on phosphorus-doped hydrogenated amorphous silicon: The effects of tunneling

A solution to the problems of roll-to-roll lithography on flexible substrates is presented. We have developed a roll-toroll
imprint lithography technique to fabricate active matrix transistor backplanes on flexible webs of polyimide that
have a blanket material stack of metals, dielectrics, and semiconductors. Imprint lithography produces a multi-level 3-
dimensional mask that is then successively etched to pattern the underlying layers into the desired structures. This
process, Self-Aligned Imprint Lithography (SAIL), solves the 
layer-to-layer alignment problem because all masking levels are created with one imprint step. The processes and equipment required for complete roll-to-roll SAIL fabrication will be described. Emphasis will be placed on the advances in the roll-to-roll imprint process which have enabled us to produce working transistor arrays.

Advances in roll-to-roll imprint lithography for display applications

A specialized processor (110) includes an objective function evaluator (112) responsive to a state vector; and a solver (116), responsive to an output of the evaluator (112), for finding an optimal solution to the state vector. The processor can form a building block of a larger system (500, 600, 700, 800, 900).

Specialized processor for solving optimization problems

Occupancy of dangling bond defects in doped hydrogenated amorphous silicon

A device that includes a layer of material having particles dispersed therein, a first electrode on a first surface of the layer, and a second electrode on a second surface of the layer opposite the first surface. A state of the particles is changed when a prescribed voltage is applied across the first and second electrodes.

Warren B. Jackson

Papers

Schottky barriers on phosphorus-doped hydrogenated amorphous silicon: The effects of tunneling

Advances in roll-to-roll imprint lithography for display applications

Specialized processor for solving optimization problems

Occupancy of dangling bond defects in doped hydrogenated amorphous silicon

Device having a state dependent upon the state of particles dispersed in a carrier