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Reported discrepancy of phase separation in In[sub x]Ga[sub 1-x]N films between experimental studies and theoretical calculations based on the usual regular solution model is discussed from the standpoint of phase diagram. The inclusion of higher-order pairwise interactions in the theoretical model may allow the system to undergo a spinodal decomposition in an asymmetrical manner as revealed by experiments. It is suggested that basal-plane atomic ordering in the In-rich precipitates should accompany the decomposition. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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 behavior of Mg dopants in InN films grown by molecular beam epitaxy was studied by Raman scattering in a wide Mg concentration ([Mg]) range from 1 × 10 16 to 4 × 10 21  cm −3 . Transition of dominant lattice sites of Mg dopants was investigated through a diffusion-collision model based on Mg-related local vibrational modes, which was further confirmed through stress analysis. It was found that Mg i and Mg In -N-In i are the dominant sites of Mg dopants at [Mg] < 1.8 × 10 20  cm −3 , while the complex of Mg In -N-Mg i dominates with further increasing [Mg]. This study provides an insight on the behavior of Mg and would be helpful for achieving effective p-type doping in InN. [ABSTRACT FROM AUTHOR]

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]

Abstract: C-axis oriented InN nanocolumns (NCs) were grown on (0001) GaN templates by molecular beam epitaxy. In situ spectroscopic ellipsometry and reflection high-energy electron diffraction demonstrated that InN NCs epitaxy was initiated from self-organized growth of InN quantum dots in Stranski–Krastanov mode, which was further confirmed by ex situ measurement of atomic force microscopy. InN NCs were of high crystal quality. The full-width at half-maximum (FWHM) value of ω-scan for (002) InN NCs showed a comparative value with that of GaN template in a range of 500–600 arcsec. [Copyright &y& Elsevier]

The terahertz (THz) emission with the maximum at the 3–5 THz is observed under electrical pumping from InN epilayers, where structural imperfections such as nanocolumns, pores, and In clusters are situated with a certain periodicity. This radiation is ascribed to the spontaneous emission of surface plasmon polariton like waves guided in thin surface/interior layers and coupled to electromagnetic field at these imperfections. These waves are generated thermally under applied electric field. The registered THz spectra and power dependences are well consistent with this plasmon-related radiation mechanism. [ABSTRACT FROM AUTHOR]

Mg-doped InN films grown by plasma-assisted molecular beam epitaxy were characterized by infrared reflectance. Signatures of p-type conductivity in the spectra were obtained in the same doping density range where the existence of net acceptors was found by electrolyte capacitance-voltage measurements. Numerical spectrum analysis, which takes into account the large broadening factor of the normal mode energies of longitudinal optical phonon–plasmon coupling yielded high hole densities in the range of (0.1–1.2)×1019 cm-3 and optical mobilities in the range of 25–70 cm2/V s. [ABSTRACT FROM AUTHOR]

The energy broadenings of the higher energy branch of the longitudinal optical (LO) phonon-plasmon coupling modes for E1(LO) and A1(LO) are analyzed for InN films by infrared reflectance and spectroscopic ellipsometry. Larger broadening for the vibration parallel to c of A1(LO)-plasmon coupling is found with the decrease in electron density. This phenomenon is caused by the plasmon lifetime anisotropy, and is attributed to the reduction in crystal defects causing isotropic carrier scattering and the remaining of defects along the c axis such as threading dislocations and columnar grain boundaries. [ABSTRACT FROM AUTHOR]

p-type conductivity control of In- and N-polar InN layers grown on GaN templates with different Mg concentrations ([Mg]) was systematically investigated by using electrolyte-based capacitance-voltage (ECV) analyses. With increasing [Mg], p-type conduction was confirmed for [Mg]s from ∼1018 to ∼3×1019 cm-3. The conduction was reversed to n type at [Mg]s above 1020 cm-3, however, due to overdoping effects introducing shallow donors in InN. Further, it was found that charges at the interface states located within forbidden band of InN greatly affected the ECV measurements resulting in overestimation of net acceptor concentrations, and some calibration was necessary to estimate them. [ABSTRACT FROM AUTHOR]

To investigate the Mg-dopability in In-polar InN epilayers grown by molecular beam epitaxy, polarity inversion dependence on Mg-doping level is studied. A multiple-InN layer-structure sample with different Mg-doping levels is grown and analyzed by transmission electron microscopy. Formation of high density V-shaped inversion domains is observed for the Mg-doped InN with Mg concentration ([Mg]) of 2.9×1019 cm-3. These domains lead to polarity inversion from In to N polarity. Further study for Mg-doped InN epilayers shows that polarity inversion takes place when [Mg] increases above 1.6×1019 cm-3. It is also shown that the Mg-sticking coefficient is almost independent of the polarity. [ABSTRACT FROM AUTHOR]

Mg doping into In-polar InN layers for different Mg fluxes is performed on GaN templates by molecular beam epitaxy, and their electrical and optical properties are investigated. Mg concentration is linearly proportional to Mg-beam flux, indicating that the Mg-sticking coefficient is almost unity. With Mg doping, electron concentration decreases by the effect of carrier compensation, but it begins to increase with further increasing Mg flux because of Mg-related donorlike-defects formation. For the partially carrier-compensated Mg-doped InN, two photoluminescence peaks are observed; one is originated from free-to-acceptor emission with an acceptor activation energy of about 61 meV and the other is similar to the conventional band-to-band emission. [ABSTRACT FROM AUTHOR]

In-polar InN films with atomically flat surface are grown on Ga-polar GaN templates by molecular beam epitaxy. Densities of threading dislocations with screw and edge components in these films are about 108 and low 1010 cm-2, respectively. It is found that the screw-component threading dislocation is the dominant cause for macroscopic surface defects appearing as growth-spiral hillocks; their densities (their growth temperature dependences) are almost the same (similar) with each other. Further, it is shown that the residual electron concentration in InN is almost the same with the density of dangling bonds at the edge-component threading dislocations. [ABSTRACT FROM AUTHOR]

The polarity of molecular-beam epitaxy grown ZnO films was controlled on nitrided c-sapphire substrate by modifying the interface between the ZnO buffer layer and the nitrided sapphire. The ZnO film grown on nitrided sapphire was proven to be Zn-polar while the O-polar one was obtained by using gallium predeposition on nitrided sapphire, which was confirmed by coaxial impact collision ion scattering spectroscopy and chemical etching effect. The Zn-polar ZnO film showed higher growth rate, slightly better quality, and different surface morphology in comparison to the O-polar one. [ABSTRACT FROM AUTHOR]

Dichloro(ethylenediamine)platinum(II), Pt(en)Cl(2), was dissolved in H(2)O and D(2)O, and the resulting aqueous solutions were electrosprayed into a quadrupole ion-trap mass spectrometer. A series of major and minor ionic hydrolysis products were detected. These ions were then subjected to collision-induced dissociation. As an aid in interpreting the experimental results, density functional theory calculations were carried out. These computations permitted the structures and energetics associated with the hydrolysis products to be determined. An understanding of the hydrolysis of PtenCl(2) and related coordination complexes is essential in the rational design of metal-based drugs.