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.

Hydrogen Induced Passivation and Generation of Defects in Polycrystalline Silicon

The dependence of capacitance transients on filling pulse width for n-type a-Si:H has been compared for devices with identical bulk n-type a-Si:H but different back contacts. The capacitance transients for devices with Ohmic Cr/n + back contacts do not exhibit any significant dependence on filling pulse width while the devices with non-Ohmic p + c-Si display the anomalous dependence previously attributed to defect relaxation. Measurements of current injection during the filling pulse indicates that charge injection is impeded by the non-Ohmic p + c-Si contacts. Variation of the filling pulse height is shown to yield apparent scaling in time, an effect previously thought to be unique to defect relaxation.

Origin of the anomalous pulse-width dependence in capacitance transient measurements on n-type a-Si:H

The valence band and conduction band density of states of hydrogenated amorphous silicon are determined using x-ray photoemission and bremstrahlung isochromat spectroscopy, respectively. From these densities of states and measurements of the imaginary part of the dielectric function using ellipsometry, the energy dependence of the average transition matrix element squared has been determined. The matrix element exhibits a maximum near the direct edge of crystalline silicon (~3.35 eV) and is very similar to the energy dependence calculated for a complex crystalline form of silicon with short range disorder and long range order.

Energy Dependence of the Optical Matrix Element for Hydrogenated Amorphous Silicon

Small temperature-induced perturbations from thermodynamic equilibrium of doped hydrogenated amorphous silicon (a-Si:H) are explored by dark conductivity measurements. The equilibration kinetics reveal significant differences between phosphorus and boron doping. Raising the temperature leads to an increase of electron/hole densities which are related to the activation of additional dopants, while a decrease of temperature causes the opposite effect of dopant passivation. The creation kinetics of P doped a-Si:H is stretched exponential with a temperature independent β value of 0.85 whereas dopant passivation in the same temperature range is also stretched exponential decay, but with values for β < 0.8. In contrast, the kinetics of boron activation and passivation are stretched exponential with equal β values. The time constant τ to achieve thermodynamic equilibrium for both activation and passivation is thermally activated with energies ≃ 1.1 eV for P and B doped a-Si:H. τ depends weakly on the degree of perturbation. A discussion and interpretation of the data based on hydrogen migration in a-Si:H is given.

Kinetics of Dopant Metastability in a-Si:H

A method for creating controlled scattering effects including (a) disposing at least one curable ink layer onto a substrate in an imagewise fashion or in a continuous film fashion; (b) applying a first cure to partially cure the ink layer (a); (c) disposing at least one scattering material onto the ink layer (a); and (d) applying a second cure to fully cure the ink layer (a); wherein the first cure and the second cure are applied in a manner to control the disposition of the scattering material on top of and penetration into the curable ink layer to control surface and subsurface scattering properties.

Warren B. Jackson

Papers

Hydrogen Induced Passivation and Generation of Defects in Polycrystalline Silicon

Origin of the anomalous pulse-width dependence in capacitance transient measurements on n-type a-Si:H

Energy Dependence of the Optical Matrix Element for Hydrogenated Amorphous Silicon

Kinetics of Dopant Metastability in a-Si:H

Printing process for preparing controlled scattering effects