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Extensive high resolution transmission and scanning transmission electron microscopy observations were performed in In(Ga)N/GaN multi-quantum well short period superlattices comprising two-dimensional quantum wells (QWs) of nominal thicknesses 1, 2, and 4 monolayers (MLs) in order to obtain a correlation between their average composition, geometry, and strain. The high angle annular dark field Z-contrast observations were quantified for such layers, regarding the indium content of the QWs, and were correlated to their strain state using peak finding and geometrical phase analysis. Image simulations taking into thorough account the experimental imaging conditions were employed in order to associate the observed Z-contrast to the indium content. Energetically relaxed supercells calculated with a Tersoff empirical interatomic potential were used as the input for such simulations. We found a deviation from the tetragonal distortion prescribed by continuum elasticity for thin films, i.e., the strain in the relaxed cells was lower than expected for the case of 1 ML QWs. In all samples, the QW thickness and strain were confined in up to 2 ML with possible indium enrichment of the immediately abutting MLs. The average composition of the QWs was quantified in the form of alloy content. [ABSTRACT FROM AUTHOR]

Time resolved scanning near-field optical microscopy was employed to study spatial and temporal dynamics of III-nitride-system-based blue light emitting laser diodes with a ridge width of 20 [mu]m deposited on high pressure grown bulk GaN substrate. The spatial and temporal chaotic behavior of the emitted laser beam in the far field limit includes the beam steering as a result of a phase tilt and the competition between adjacent modes.

Structural and electronic properties of MgZnO and BeMgZnO alloys are studied by the ab-initio Density Functional Theory method. Large band gap bowings are found for both kinds of alloys. The total energies as functions of the lattice constants are calculated and used to determine the ranges of composition in which the alloys are stable in the wurtzite structure. It is shown that the addition of 6% of Be can already help in stabilization of the MgZnO alloy in the wurtzite structure. The band gap can reach 7 eV for the wurtzite BexMg0.5Zn0.5-xO alloys with x approaching 0.5 and about 5.0 eV for Be0.125MgxZn0.875-xO type alloys for x approaching 0.6. Varying the alloy composition according to the presented stabilization diagram showing ranges of the x, y, for which BexMgyZn1-x-yO is stable in the wurtzite phase, one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering. [ABSTRACT FROM AUTHOR]

Mg doped gallium-nitride single crystals were studied to determine temperature dependence of the electrical properties.

High-pressure and high-temperature annealing of Mg/P-implanted GaN films was monitored using visible and ultraviolet micro-Raman scattering.

In this paper we review the recent studies on wide InGaN quantum wells (QWs). InGaN QWs are known to suffer from an extremely high built-in piezoelectric polarization, which separates the electron and hole wavefunctions and causes the quantum-confined Stark effect. We show both by means of modeling and experimentally, that wide InGaN QWs can have quantum efficiency superior to commonly used thin QWs. The high efficiency is explained by initial screening of the piezoelectric field and subsequent emergence of optical transitions involving the excited states of electrons and holes, which have a high oscillator strength. A high pressure spectroscopy and photocurrent measurements are used to verify the mechanism of recombination through excited states. Furthermore, the influence of QW width on the properties of optoelectronic devices is studied. In particular, it is shown how the optical gain forms in laser diodes with wide InGaN QWs. [ABSTRACT FROM AUTHOR]

Optical-absorption analysis of energy gap in bulk single crystals of GaN and an epitaxial layer grown on a sapphire substrate indicates temperature dependence of the absorption edge and the importance of free-electron concentrations to absorption edge positions. The different free-electron concentrations of bulk single crystals and the epitaxial layer lead to their varying negative temperature coefficients. Variation of absorption edge and temperature dependence of the absorption edge in various GaN samples are explained by the Burstein- Moss effect. The strong nonlinear shift of energy gap with temperature, noted even at high temperatures, is due to the high Debye temperature of GaN crystals.