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InN epilayers grown by radio-frequency (rf) plasma assisted molecular beam epitaxy under different surface stoichiometries were characterized using in situ spectroscopic ellipsometry. It was found that the pseudodielectric functions were affected by the surface stoichiometrry and both real and imaginary parts of the dielectric functions tended to be larger with increasing In-beam flux.

Research was conducted on the implications of the growth rate of a GaN buffer layer grown on a GaN epilayer. Findings show that a significant role is performed by the growth rate in the improvement of the quality of the GaN film on a sapphire substrate. Also, the optimum growth rate which yields the best quality was discovered. The promotion of the lateral growth mode illustrate the improvements in the qualities of the GaN film.

Infrared (IR) reflectance and transmission spectra of Mg doped InN films are analyzed using a dielectric function consisting of the terms of phonon, plasmon, and electronic transition between the valence band and the acceptor levels. The reflectance spectra at lower temperatures than 200 K are highly affected by the electronic transition. Acceptor activation energy Ea decreases with the increase in ionized acceptors because of the Coulomb potential overlap of acceptors charged by the background electrons and/or hole generation by the temperature increase. It is found that Ea is 69(±5) meV at low Mg- density limit and decreases to 50 meV at 5 K because of the charging by the background electrons of the density of 1 × 1018 cm-3. Temperature increase causes the further decrease in Ea, which causes the high hole density of the order of 1018 cm-3 at room temperature in spite of the high degeneracy of the acceptor states. The heavy hole mass is obtained as 0.59(±0.06)m0. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) spectra of In-polar n-type InN films with different dislocation and residual electron densities are investigated in the temperature range 15–300 K. The dependence of PL intensity on temperature is analyzed by using a model function that is based on rate equations for photoexcited hole density. By considering the relation between the dislocation densities estimated from the widths of the peaks of x-ray ω-rocking curves and the parameters obtained from the rate equations, two kinds of nonradiative carrier recombination processes are identified. One process is independent of threading dislocations and is thermally activated, while the other takes place in the vicinity of edge-type dislocations and requires no activation energy. [ABSTRACT FROM AUTHOR]

The infrared reflectance spectra of InN/GaN structures are analyzed in two energy regions for higher and lower energy branches of the longitudinal optical phonon-plasmon coupled modes. For samples with smaller residual electron density than 5×1017 cm-3 and the film thickness of 0.7–4 μm, the spectra down to 200 or 250 cm-1 shows the existence of the electron accumulation with sheet electron density of 1013 cm-2 in the vicinity of the InN/GaN-interface. The effect of the surface electron accumulation on the spectra is not identified, which is possibly caused by the small mobility of the order of 10 cm2/V s or less for the surface electrons. The electron density of the inside bulk region is obtained with account of this interface accumulation. However, for samples with higher electron density and thickness of several micrometers a model with uniform electron density well reproduce the experimental spectra. With this spectrum fitting we extract the electron properties inside the bulk region for samples with the thickness of about 700 nm or larger. [ABSTRACT FROM AUTHOR]

In-polarity InN/In0.7Ga0.3N multiquantum wells (MQWs) were fabricated on a thick In0.7Ga0.3N interlayer/Ga-polarity GaN template by radio-frequency plasma-assisted molecular beam epitaxy. We then investigated how the lattice relaxation and piezoelectric field in InN wells affect their structural and photoluminescence (PL) properties, respectively. It was found that the critical thickness of InN well on In0.7Ga0.3N barrier was about 1 nm. A clear PL peak shift from 1.40 to 1.95 μm was observed depending on the InN well thickness from 0.7 to 2.0 nm. Correspondingly, PL-intensity reduction was also observed with increasing well thickness. No PL was observed for the sample with 4.1 nm thick InN wells. On the basis of theoretical estimation of transition energies in InN/In0.7Ga0.3N MQWs, it was confirmed that the quantum-confined Stark effect (QCSE) played an important role for both the observed PL peak shift and the decrease in intensity. The piezoelectric field in coherently grown InN wells was about 3 MV/cm but it was reduced to about 1–2 MV/cm for the samples with relaxed InN wells. It was confirmed that the InN wells must be thinner than the critical thickness (1 nm) in following two points: to reduce defects arising from lattice relaxation and to reduce QCSE leading to emission-peak redshift and a decrease in intensity. [ABSTRACT FROM AUTHOR]

Effect of growth temperature on 2.3 μm thick N-polar InN films grown on GaN template at 440–620 °C by plasma-assisted molecular beam epitaxy was investigated. We found different growth behaviors depending on the growth temperatures, which greatly influenced surface morphology. The surface showed dendritic morphologies at temperatures lower than 540 °C while step-flow-like morphologies and spiral growth were clearly observed at temperatures higher than 540 °C. Crystalline quality was improved with increasing growth temperature up to 540 °C and was almost saturated at higher temperatures. A gradual blueshift of the emission peak was observed from 13 K photoluminescence (PL) spectra with increasing growth temperature, which was due to the increased compressive strain in InN films. A Poisson ratio (ν=0.21±0.05) for InN and a slope of PL peak energy as a function of [variant_greek_epsilon]c (δE/δ[variant_greek_epsilon]c=18.9 eV) were obtained. Our results indicated that the epitaxial temperatures of 540–600 °C were best to achieve high quality InN films with a smooth surface. [ABSTRACT FROM AUTHOR]

InN epilayers grown by radio-frequency plasma-assisted molecular beam epitaxy under different surface stoichiometries were characterized by in situ spectroscopic ellipsometry in the range from 0.731 eV (1697 nm) to 4.95 eV (250 nm). Nitrogen polarity InN epilayers were grown at 600 °C on GaN-underlayer/sapphire substrate. The surface stoichiometry during growth was changed by varying the indium-beam flux under the same nitrogen-beam flux. It was found that the pseudodielectric functions were drastically affected by the surface stoichiometry. The dielectric functions of InN grown under different stoichiometries were obtained. Both real and imaginary parts of the dielectric functions tended to be larger with increasing In-beam flux. [ABSTRACT FROM AUTHOR]

The cathodoluminescence (CL) properties of Ce-activated strontium thiogallate (SrGa[sub 2]S[sub 4]:Ce) thin films have been investigated aiming towards phosphor screen application in an emissive display under low to medium accelerating voltage (<5 kV) excitation. The SrGa[sub 2]S[sub 4]:Ce thin films were grown by multisource deposition using a molecular beam epitaxy system. The growth temperature of the CL phosphor thin films was 472.5 °C, which is the lowest value ever achieved. Several related properties were observed, including the CL spectra, luminance, luminous efficacy, and surface morphology of the thin films. A luminance of 1000 cd/m² and an efficacy of 1 lm/W were obtained at an accelerating voltage of 5 kV with a current density of 60 µA/cm². The light-outcoupling efficiency (η[sub out]) of the film was 0.0531. In spite of this small η[sub out] of the films compared to that of powder phosphors, the luminance and efficacy were comparable to the conventional ZnS:Ag, Cl powder phosphor. The average grain size of the films was 0.14 µm × 0.04 µm. The high luminance and luminous efficacy of the films with their submicron grain size is useful to realize high-resolution emissive displays. [ABSTRACT FROM AUTHOR]

The fabrication and the lattice relaxation and piezoelectric field properties of In-polarity InN/[In.sub.0.7][Ga.sub.0.3]N multiquantum wells (MQWs) on a thick [In.sub.0.7][Ga.sub.0.3]N interlayer/Ga-polarity GaN template are described. It is shown that the InN wells should be thinner than the critical thickness in order to reduce defects from lattice relaxation and to reduce quantum-confined Stark effect (QCSE) leading to emission-peak redshift and a decrease in intensity.

Provides information on a study that focused on iodine-doped zinc selenide films, which have been grown on gallium arsenide by low-pressure metalorganic vapor-phase epitaxy using dimethylzinc and hydrogen selenide as reactants. Motive for using ethyliodide diluted to 1000 pulse per minute; Origin of blue emission; Characteristics of zinc selenide; Superiority of group-VII elements.

The growth kinetics and structural perfection of (InN)1/(GaN)1-20 short-period superlattices (SPSs) were investigated with their application to ordered alloys in mind. The SPSs were grown on +c-GaN template at 650 °C by dynamic atomic layer epitaxy in conventional plasma-assisted molecular beam epitaxy. It was found that coherent structured InN/GaN SPSs could be fabricated when the thickness of the GaN barrier was 4ML or above. Below 3ML, the formation of SPSs was quite difficult owing to the increased strain in the SPS structure caused by the use of GaN as a template. The effective or average In composition of the (InN)1/(GaN)4 SPSs was around 10%, and the corresponding InN coverage in the ~1 ML-thick InN wells was 50%. It was found that the effective InN coverage in ~1 ML-thick InN wells could be varied with the growth conditions. In fact, the effective In composition could be increased up to 13.5%, i.e., the corresponding effective InN coverage was about 68%, by improving the capping/freezing speed by increasing the growth rate of the GaN barrier layer. [ABSTRACT FROM AUTHOR]