We established the angular conditions that maintain the quasi-phase matching conditions for enhanced second-harmonic generation. To do that, we investigated the equifrequency surfaces of the resonant ...Bloch modes of a two-dimensional periodic, hole-array photonic crystal etched into a GaN/sapphire epitaxial structure. The equifrequency surfaces exhibit remarkable shapes, in contrast to the simpler surfaces of a one-dimensional structure. The observed anisotropy agrees well with the surfaces calculated by a scattering matrix method. The equifrequency surfaces at fundamental and second-harmonic frequencies provide the values of polar and azimuthal angles that maintain quasi-phase matching conditions for enhanced second-harmonic generation over an extended tuning range. The predicted values for quasi phase-matching conditions show that frequency tuning for the two-dimensional case covers an about two times larger fractional bandwidth relative to the one-dimensional case.
We report on results of the fabrication and the micro-reflectance measurement of GaN photonic crystals. The etching performance of GaN has been studied with a conventional reactive ion etching system ...and SiCl
4 plasma. We obtained an etch rate of 100 nm/min and etching depth of 600 nm for dense GaN pillars. With graphite lattice of 270 nm period we observed a high reflection peak in the region of 400 nm wavelengths, depending strongly on the incident light polarization, which is in a good agreement with the theoretical calculation.
We present the first experimental study of the exciton spin relaxation dynamics in InGaN/GaN multiple quantum well structures after quasi‐resonant picosecond excitation with linearly polarized light. ...Whereas short spin‐relaxation times are generally expected in GaN‐based bulk structures, for multiple quantum well structures we found long spin‐relaxation times, around 100 ps, when the indium content was not too high. Our results suggest that the energy relaxation toward the radiative state can preserve the linear polarization of the exciton.
Photonic crystals are a new class of materials where photonic band gaps, large dispersion and anisotropy occur. By exploiting these properties GaN photonic crystals should have important potential ...for optoelectronic applications, principally in the areas of high-efficiency light emitters and second-harmonic generators. We present measurements of the equifrequency surfaces of the radiative Bloch modes for a photonic crystal etched in a GaN/sapphire film. The photonic band structure is calculated by using a scattering matrix method that reproduces well the anisotropy of the equifrequency surfaces exhibited by the photonic crystal.
We report experimental results for the dispersion of Bloch modes in two-dimensional photonic crystals consisting of pillars in a graphite arrangement deeply etched into an asymmetric ...gallium–arsenide-based waveguide film. The quality factor
Q of a confined mode that cannot be excited using normally incident plane waves (because of its spatial symmetry mismatch) has been estimated over a significant part of the Brillouin zone.
Wurtzite GaN on (0001) sapphire is studied by mean of reflectance and magnetocircular dichroism up to 5.5 T at 2 K. This very powerful technique allows us to determine the Zeeman splittings, for the ...first time to our knowledge, to be about 0.05 meV/T for the
X
A and
X
C excitons and almost zero for the
X
B exciton.
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