The initial discovery by Bednorz and Muller1 of 35-K superconductivity in the La-Ba-Cu-O system has stimulated worldwide activity in searching for higher-temperature superconductors. Elemental substitution has proved to be most effective in raising transition temperature. Substitution of Sr for Ba has produced 40-K superconductivity2–5and substitution of Y for La has produced a new high-temperature superconductor with transition temperature above liquid-nitrogen temperature6. A class of superconducting compounds of the form RBa2Cu307-x has been explored by further substitutions of other rare earths (Y is considered in the rare-earth [RI category here) for Y7-13. To date, a rare earth, an alkaline earth, copper and oxygen have been required for all high-temperature superconductors14,15. (Zhanget al 14reported 90-K superconductivity in the Th-Ba-Pb(Zr)-Cu-O system. Panetal15reported 50-K superconductivity in the Y-Ba-Ag-O system. As Th is a member of the actinide series which belongs to the same Group 3B in the periodic table as the lanthanide series and Ag belongs to the same Group 1B as Cu, high-temperature supercon-ductors are still thought to be closed in the Group 3B—Group 2A-Group 1B—oxygen system. ) Only partial substitutions ha. e led to superconductors, but with no significant rise of transition tem-perature (the only exception is 40-K superconductivity in La2CuO4-x , refs 16, 17). Here we report superconductivity in the rare-earth-free TI-Ba-Cu-O system. We have obsened sharp drops of resistance starting above 90 K with zero resistance at 81 K in this system. Magnetic measurements have confirmed that these sharp drops of resistance in the TI-Ba-Cu-O samples origi-nate from superconductivity. The samples are stable in air for at least two months, and their preparation is easily reproduced.

Superconductivity in the rare-earth-free Tl–Ba–Cu–O system above liquid-nitrogen temperature

An extensive review is given of the results from literature on electron beam induced deposition. Electron beam induced deposition is a complex process, where many and often mutually dependent factors are involved. The process has been studied by many over many years in many different experimental setups, so it is not surprising that there is a great variety of experimental results. To come to a better understanding of the process, it is important to see to which extent the experimental results are consistent with each other and with the existing model. All results from literature were categorized by sorting the data according to the specific parameter that was varied (current density, acceleration voltage, scan patterns, etc.). Each of these parameters can have an effect on the final deposit properties, such as the physical dimensions, the composition, the morphology, or the conductivity. For each parameter-property combination, the available data are discussed and (as far as possible) interpreted. By combining models for electron scattering in a solid, two different growth regimes, and electron beam induced heating, the majority of the experimental results were explained qualitatively. This indicates that the physical processes are well understood, although quantitatively speaking the models can still be improved. The review makes clear that several major issues remain. One issue encountered when interpreting results from literature is the lack of data. Often, important parameters (such as the local precursor pressure) are not reported, which can complicate interpretation of the results. Another issue is the fact that the cross section for electron induced dissociation is unknown. In a number of cases, a correlation between the vertical growth rate and the secondary electron yield was found, which suggests that the secondary electrons dominate the dissociation rather than the primary electrons. Conclusive evidence for this hypothesis has not been found. Finally, there is a limited understanding of the mechanism of electron induced precursor dissociation. In many cases, the deposit composition is not directly dependent on the stoichiometric composition of the precursor and the electron induced decomposition paths can be very different from those expected from calculations or thermal decomposition. The dissociation mechanism is one of the key factors determining the purity of the deposits and a better understanding of this process will help develop electron beam induced deposition into a viable nanofabrication technique.

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A critical literature review of focused electron beam induced deposition

In order to clarify the effect of metal oxide support on the catalytic activity of gold for CO oxidation, gold has been deposited on SiO2 with high dispersion by chemical vapor deposition (CVD) of an organo-gold complex. Comparison of Au/SiO2 with Au/Al2O3 and Au/TiO2, which were prepared by both CVD and liquid phase methods, showed that there were no appreciable differences in their catalytic activities as far as gold is deposited as nanoparticles with strong interaction. The perimeter interface around gold particles in contact with the metal oxide supports appears to be essential for the genesis of high catalytic activities at low temperatures.

Chemical vapor deposition of gold on Al2O3, SiO2, and TiO2 for the oxidation of CO and of H2

A thorough discussion of the various features of the photoluminescence spectra of undoped, p‐doped and n‐doped AlxGa1−xAs (0≤x≤1) alloys is given. This review covers spectral features in the energy region ranging from the energy band gap down to ≂0.8 eV, doping densities from isolated impurities to strongly interacting impurities (heavy‐doping effects) and lattice temperatures from 2 to 300 K. The relevance of photoluminescence as a simple but very powerful characterization technique is stressed also in comparison with other experimental methods. The most recent determinations of the Al concentration dependence of some physical properties of the alloy (energy gaps, carrier effective masses, dielectric constants, phonon energies, donor and acceptor binding energies, etc.) are given. The main physical mechanisms of the radiative recombination process in semiconductors are summarized with particular emphasis on the experimental data available for AlxGa1−xAs. The effects of the nature of the band gap (direct ...

Photoluminescence of AlxGa1−xAs alloys

The present disclosure relates to a semiconductor light emitting device, comprising: a plurality of semiconductor layers, including a first semiconductor layer having a first conductivity, a second semiconductor layer having a second conductivity different from the first conductivity, and an active layer interposed between the first semiconductor layer and the second semiconductor layer, generating light via electron-hole recombination; a first electrode, supplying either electrons or holes to the plurality of semiconductor layers; a second electrode, supplying, to the plurality of semiconductor layers, electrons if the holes are supplied by the first electrode, or holes if the electrons are supplied by the first electrode; a non-conductive distributed bragg reflector coupled to the plurality of semiconductor layers, reflecting the light from the active layer; and a first light-transmitting film coupled to the distributed bragg reflector from a side opposite to the plurality of semiconductor layers with respect to the non-conductive distributed bragg reflector, with the first light-transmitting film having a refractive index lower than an effective refractive index of the distributed bragg reflector.

Semiconductor Light Emitting Device

Growth of GaAs VPE layers with high thickness uniformity

The EL2 concentration in GaAs grown by metalorganic vapor‐phase epitaxy (MOVPE) using tertiarybutylarsine (tBAs) was measured by deep‐level transient spectroscopy. EL2 concentration decreases monotonically with increasing growth temperature. Taking the origin of EL2 into consideration, we discuss the growth mechanisms of MOVPE using tBAs. The EL2 concentration is affected by the incorporation of excess As into the crystal, and, therefore, depends on the kind of reactant on the surface. We propose a model in which the reactant on the surface changes from As2H2 to As2 with increasing temperature. The temperature dependence of EL2 concentration is explained by our model where As2 dissociates into atomic As on the surface and As2H2 gives excess As in the crystal.

Growth temperature dependence of EL2 concentration in GaAs grown by metalorganic vapor‐phase epitaxy using tertiarybutylarsine

A field-effect transistor with a 2 μm Au gate was fabricated on a selectively doped InP/GaInAs heterostructure grown using chloride transport vapour-phase epitaxy. Complete pinch-off was observed, and transconductance of 90 and 160 mS/mm were measured at 295 and 77 K, respectively. From analysis of the drain I/V characteristic, two-dimensional electron gas at the interface was revealed to be the dominant factor for the channel current. This is the first report of a successful preparation of an n+ InP/n- GaInAs heterostructure for the selectively doped field-effect transistor.

Selectively doped n+ InP/n- GaInAs heterostructure prepared using chloride transport vapour-phase epitaxy

The photoluminescence and, for the first time, the excitation spectra of In0.53Ga0.47As/InP multi-quantum-well structures were measured at 4.2 K. Emission bands were observed below E1h as well as at E1h, where E1h denotes the n = 1 electron-heavy-hole free-exciton transition. The emission below E1h was found from the excitation spectra to be in striking contrast to the band-acceptor transition in thick In0.53Ga0.47As layers. Its luminescent intensity decreases very slowly or show little decrease as the photon energy of excitation decreases below E1h. This emission is believed to be related to the n = 1 electron quantum state-acceptor transition. Fluctuation of quantum levels due to strain in the interdiffused layers at the heterointerfaces is thought to be a possible origin of the anomalous excitation spectra.

Photoluminescence excitation spectroscopy of In0.53Ga0.47As/InP multi-quantum-well heterostructures

We have applied kinetic simulation to MOCVD chemistry in a horizontal MOCVD reactor. Both chemical reactions and material diffusion are considered. For trimethylgallium decomposition, concentrations of chemical species reach their steady state values which differ largely from the equilibrium values.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S194642740047209X

Junji Komeno

Papers

Growth of GaAs VPE layers with high thickness uniformity

Growth temperature dependence of EL2 concentration in GaAs grown by metalorganic vapor‐phase epitaxy using tertiarybutylarsine

Selectively doped n+ InP/n- GaInAs heterostructure prepared using chloride transport vapour-phase epitaxy

Photoluminescence excitation spectroscopy of In0.53Ga0.47As/InP multi-quantum-well heterostructures

Gas Phase Reactions in Horizontal MOCVD Reactors