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. (C) 2002 Elsevier Science B.V. All rights reserved.

We report the successful infilling of opal which consists of a fee arrangement of silica spheres with the semiconductor GaN by MOCVD technique. The angular dispersion of the Bragg diffracted light was studied for bare opal and GaN infilled opal by measuring reflection spectra at different external angles with respect to the [1 1 1] direction. The Bragg's law gives an estimation of 4.5% of void volume filled by the GaN. The crystal inhibits the yellow emission of GaN in the energies of the photonic gap. This decrease in the PL signal has one strong sensibility to the collection angle variation. This dependence is a signature of the GaN inside the opal voids.

We report the fabrication of submicon-scale structures using high resolution etching to transfer patterns from PMMA into GaN with an intermediate mask consisting of a bilayer of titanium and SiNx. Atomic force microscopy measurements showed the high quality of the structures etched in CH4/H-2 as well as an erosion of the mask. The low temperature photoluminescence measured on the etched structures was almost as strong as that from the unetched surface. (C) 1999 Elsevier Science S.A. All rights reserved.

We report a low temperature and room temperature photoluminescence (PL) study of a series of two-dimensional arrays of holes and pillars in a triangular lattice arrangement, fabricated in a 1.8 mu m thick GaN/sapphire epilayer. The sample was patterned by electron beam lithography and reactive ion etching in a CH4/H-2 plasma. Such structures with periodic variation of the dielectric constant may give rise to photonic crystals that can create a range of forbidden frequencies called a photonic bandgap. We have used the PL peak to evaluate the damage introduced onto the semiconductor by the etching procedure, and to determine the magnitude of the relaxation of the strain in the GaN film. Theoretical computations predict the photonic bandgap positions for future experimental investigations.

We have demonstrated a process for the fabrication of sub-micron structures using high resolution etching to transfer patterns by masking with a bilayer of Titanium and SiNX. Reactive ion etching (RIE) was performed on GaN epilayers grown on (0001) sapphire by metal organic vapour phase epitaxy (MOVPE). Various chemistries were used to etch GaN including: HBr, SiCl4/HBr, CH4/H-2, NH3/CH4/H-2 and CH4/H-2/O-2 I?Patterns including pillars, holes and gratings with feature: sizes ranging from 200 nm to 1 mu m were produced. In a CH4/H-2 plasma, quasi-vertical etching was achieved with sidewall angles greater than 81 degrees.

Wurtzite GaN on (0001) sapphire is studied by means of reflectance and magnetocircular dichroism up to 5.5 T at 2 K. This very powerful technique allows us to determine the Zeeman splittings to be about 0.05 meV/T for the X-A and X-C excitons and almost zero for the X-B exciton. Reflectance and dichroism are interpreted with a model of Gaussian dispersion of the excitonic energies and are in excellent agreement with previously proposed band-edge models.

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. (C) 1997 Elsevier Science S.A.