Roughness-induced energetic disorder at the metal/organic interface

The amplitude of the roughness-induced energetic disorder at the metal/organic interface is calculated. It was found that for moderately rough electrodes, the correction to the electrostatic image potential at the charge location is small. For this reason, roughness-induced energetic disorder cannot noticeably affect charge carrier injection, contrary to the recent reports.This work was supported by the ISTC Grant No. 2207 and RFBR grants 05-03-33206 and 03-03-33067. The research described in this publication was made possible in part by Award No. RE2-2524-MO-03 of the U.S. Civilian Research & Development Foundation for the Independent States of the Former Soviet Union (CRDF)

Novel GaN-based vertical heterostructure field effect transistor structures using crystallographic KOH etching and overgrowth

A novel V-groove vertical heterostructure field effect transistor structure is proposed using semi-polar (11-22) GaN. A crystallographic potassium hydroxide self-limiting wet etching technique was developed to enable a damage-free V-groove etching process. An AlGaN/GaN HFET structure was successfully regrown by molecular beam epitaxy on the V-groove surface. A smooth AlGaN/GaN interface was achieved which is an essential requirement for the formation of a high mobility channel.This work was funded by the Engineering and Physical Sciences Research Council (EPSRC), United Kingdom, under EP/K014471/1 (Silicon Compatible GaN Power Electronics)

Characterization of p-GaN1−x_{1−x} Asx_{x}/n-GaN PN junction diodes

The structural properties and electrical conduction mechanisms of p-type amorphous GaN$_{1−x}$ As$_{x}$ /n-type crystalline GaN PN junction diodes are presented. A hole concentration of 8.5 × 10$^{19}$ cm$^{-3}$ is achieved which allows a specific contact resistance of 1.3 × 10$^{-4}$ Ω cm$^{2}$. An increased gallium beam equivalent pressure during growth produces reduced resistivity but can result in the formation of a polycrystalline structure. The conduction mechanism is found to be influenced by the crystallinity of the structure. Temperature dependent current voltage characteristics at low forward bias (<0.35 V) show that conduction is recombination dominated in the amorphous structure whereas a transition from tunneling to recombination is observed in the polycrystalline structure. At higher bias, the currents are space charge limited due to the low carrier density in the n-type region. In reverse bias, tunneling current dominates at low bias (<0.3 V) and recombination current becomes dominant at higher reverse bias.This work was undertaken with support from the EPSRC (EP/K014471/1)

Exciton properties in zincblende InGaN-GaN quantum wells under the effects of intense laser fields

ABSTRACT: In this work, we study the exciton states in a zincblende InGaN/GaN quantum well using a variational technique. The system is considered under the action of intense laser fields with the incorporation of a direct current electric field as an additional external probe. The effects of these external influences as well as of the changes in the geometry of the heterostructure on the exciton binding energy are discussed in detail

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe

Study of eta-eta ' mixing from measurement of B-(s)(0) -&gt; J/psi eta((')) decay rates

A study of B and Bs meson decays into J/ψ η and J/ψ η′ final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, collected by the LCHb experiment and corresponding to 3.0 fb−1 of integrated luminosity. The decay B0 → J/ψ η′ is observed for the first time. The following ratios of branching fractions are measured: B(B0→J/ψη′)B(B0s→ J/ψη′)=(2.28±0.65 (stat)±0.10 (syst)±0.13 (fs/fd))×10−2,B(B0→ J/ψη)B(B0s→ J/ψη)=(1.85±0.61 (stat)±0.09 (syst)±0.11 (fs/fd))×10−2, where the third uncertainty is related to the present knowledge of fs/fd, the ratio between the probabilities for a b quark to form a Bs or a B0 meson. The branching fraction ratios are used to determine the parameters of η − η′ meson mixing. In addition, the first evidence for the decay Bs → ψ(2S)η′ is reported, and the relative branching fraction is measured, B(B0s→ ψ(2S)η′)B(B0s→ J/ψη′)=(38.7±9.0 (stat)±1.3 (syst)±0.9(B))×10−2, where the third uncertainty is due to the limited knowledge of the branching fractions of J/ψ and ψ(2S) mesons

Roughness-induced energetic disorder at the metal/organic interface

The amplitude of the roughness-induced energetic disorder at the metal/organic interface was calculated. It was found that for moderately rough electrodes, the correction to the electrostatic image potential at the charge location is small. As a result, roughness-induced energetic disorder does not noticeably affect charge carrier injection. © 2006 The American Physical Society

Transport energy in disordered organic materials

Applicability of the concept of the transport energy to charge carrier transport in disordered organic materials has been reexamined. We showed that because of a strong spatial correlation in the distribution of the site energies in organic materials the transport energy does not exist. © 2006 WILEY-VCH Verlag GmbH & Co, KGaA

Energetic disorder at the interface between disordered organic material and metal electrode

The physics of organic disordered materials is dominated by the effects of energetic disorder. We show that image forces reduce the electrostatic component of the total energetic disorder near an interface with a metal electrode. Typically, the standard deviation of energetic disorder is dramatically reduced at the first few layers of organic semiconductor molecules adjacent to the metal electrode. This means that the use of bulk disorder parameters (such as standard deviation of disorder) for description of the energetic disorder at the interface is poorly justified even in the case of identical spatial and chemical structure of the organic material at the interface and in the bulk of the transport layer. Implications for charge injection into organic semiconductors are discussed. © 2007 Old City Publishing. Inc

Energetic disorder at the metal-organic semiconductor interface

The physics of organic semiconductors is dominated by the effects of energetic disorder. We show that image forces reduce the electrostatic component of the total energetic disorder near an interface with a metal electrode. Typically, the variance of energetic disorder is dramatically reduced at the first few layers of organic semiconductor molecules adjacent to the metal electrode. Implications for charge injection into organic semiconductors are discussed. © 2006 The American Physical Society