Electroluminescent (EL)devices are constructed using multilayer organic thin films. The basic structure consists of a hole‐transport layer and a luminescent layer. The hole‐transport layer is an amorphous diamine film in which the only mobile carrier is the hole. The luminescent layer consists of a host material, 8‐hydroxyquinoline aluminum (Alq), which predominantly transports electrons. High radiance has been achieved at an operating voltage of less than 10 V. By doping the Alq layer with highly fluorescent molecules, the EL efficiency has been improved by about a factor of 2 in comparison with the undoped cell. Representative dopants are coumarins and DCMs. The ELquantum efficiency of the doped system is about 2.5%, photon/electron. The EL colors can be readily tuned from the blue‐green to orange‐red by a suitable choice of dopants as well as by changing the concentration of the dopant. In the doped system the electron‐hole recombination and emission zones can be confined to about 50 A near the hole‐transport interface. In the undoped Alq, the EL emission zone is considerably larger due to excitondiffusion. The multilayerdopedEL structure offers a simple means for the direct determination of excitondiffusion length.

Electroluminescence of doped organic thin films

An electroluminescent device is disclosed having a luminescent zone of less than one μm in thickness comprised of an organic host material capable of sustaining hole-electron recombination and a fluorescent material capable of emitting light in response to energy released by hole-electron recombination.

Electroluminescent device with modified thin film luminescent zone

I. Introduction (Preface, Nanostructures in Si Inversion Layers, Nanostructures in GaAs-AlGaAs Heterostructures, Basic Properties). 
II. Diffusive and Quasi-Ballistic Transport (Classical Size Effects, Weak Localization, Conductance Fluctuations, Aharonov-Bohm Effect, Electron-Electron Interactions, Quantum Size Effects, Periodic Potential). 
III. Ballistic Transport (Conduction as a Transmission Problem, Quantum Point Contacts, Coherent Electron Focusing, Collimation, Junction Scattering, Tunneling). 
IV. Adiabatic Transport (Edge Channels and the Quantum Hall Effect, Selective Population and Detection of Edge Channels, Fractional Quantum Hall Effect, Aharonov-Bohm Effect in Strong Magnetic Fields, Magnetically Induced Band Structure).

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Quantum Transport in Semiconductor Nanostructures

Publisher Summary Quantum transport is conveniently studied in a two-dimensional electron gas (2DEG) because of the combination of a large Fermi wavelength and large mean free path. Semiconductor nanostructures are unique in offering the possibility of studying quantum transport in an artificial potential landscape. This is the regime of ballistic transport in which scattering with impurities are neglected. The chapter presents a self-contained account of these three novel transport regimes in semiconductor nanostructures. The study of quantum transport in semiconductor nanostructures is motivated by more than scientific interest. The fabrication of nanostructures relies on sophisticated crystal growth and lithographic techniques that exist because of the industrial effort toward the miniaturization of transistors. Conventional transistors operate in the regime of classical diffusive transport, which breaks down on short length scales. The discovery of novel transport regimes in semiconductor nanostructures provides options for the development of innovative future devices.

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Since the first days of high-Tc superconductivity, the materials science and the physics of grain boundaries in superconducting compounds have developed into fascinating fields of research. Unique electronic properties, different from those of the grain boundaries in conventional metallic superconductors, have made grain boundaries formed by high-Tc cuprates important tools for basic science. They are moreover a key issue for electronic and large-scale applications of high-Tc superconductivity. The aim of this review is to give a summary of this broad and dynamic field. Starting with an introduction to grain boundaries and a discussion of the techniques established to prepare them individually and in a well-defined manner, the authors present their structure and transport properties. These provide the basis for a survey of the theoretical models developed to describe grain-boundary behavior. Following these discussions, the enormous impact of grain boundaries on fundamental studies is reviewed, as well as high-power and electronic device applications.

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Grain boundaries in high- T c superconductors

We demonstrate the self-assembled formation of concentric quantum double rings with high uniformity and excellent rotational symmetry using the droplet epitaxy technique. Varying the growth process conditions can control each ring's size. Photoluminescence spectra emitted from an individual quantum ring complex show peculiar quantized levels that are specified by the carriers' orbital trajectories.

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Self-assembly of concentric quantum double rings

Fabrication of ultra-high density InAs-stacked quantum dots by strain-controlled growth on InP(3 1 1)B substrate

It has been shown that single domain GaAs can be grown on Si(100) which consists of two domains. A mechanism for self-annihilation of the antiphase boundary in the process of GaAs growth has been proposed to explain the experimental result.

https://iopscience.iop.org/article/10.1143/JJAP.26.L944/pdf

Self-Annihilation of Antiphase Boundary in GaAs on Si(100) Grown by Molecular Beam Epitaxy

Low-temperature cleaning of GaAs substrate by atomic hydrogen irradiation has been demonstrated. Atomic hydrogen was provided by dissociation of hydrogen gas, which was carried out in a simple cracking cell with a 1500°C tungsten filament. Auger electron spectroscopy showed that carbon was removed at 200°C and oxygen was removed at 400°C by 30-min atomic hydrogen irradiation. The surface cleaning of GaAs was confirmed by the change of RHEED pattern from halo to streak after the hydrogen irradiation.

https://iopscience.iop.org/article/10.1143/JJAP.30.L402/pdf

Low-Temperature Cleaning of GaAs Substrate by Atomic Hydrogen Irradiation

Effect of Si-doping levels and annealing temperature on disordering of 150-A AlAs/150-A GaAs superlattices is studied. The doping level of 4×1018 cm-3 cause disorder for 800°C, 2 h annealing, while the doping level of 1×1018 cm-3 does not induce disorder on this annealing condition. A superlattice which is doped with 1×1019 Si cm-3 disintegrates after 650°C, 2 h annealing and the diffusion coefficient of Al–Ga interdiffusion is estimated to be 3×10-17 cm2s-1. For 800°C, 2 h annealing the two undoped AlAs/GaAs layers adjacent to the doped region are disordered by Si diffusion.

Mitsuo Kawabe

Papers

Self-assembly of concentric quantum double rings

Fabrication of ultra-high density InAs-stacked quantum dots by strain-controlled growth on InP(3 1 1)B substrate

Self-Annihilation of Antiphase Boundary in GaAs on Si(100) Grown by Molecular Beam Epitaxy

Low-Temperature Cleaning of GaAs Substrate by Atomic Hydrogen Irradiation

Disordering of Si-Doped AlAs/GaAs Superlattice by Annealing