Reactive ion etching RIE using a CH4–H2 plasma is investigated for the fabrication of a GaN one-dimensional 1D photonic crystal PhC slab. The dominant control parameter for the etch rate and the sidewall profile is the dc bias. The influence of operating pressure, CH4/H2 ratio, and total gas flow rate on the etching characteristics is also presented. An etch rate as high as 85 nm/min and an overcut angle as low as 5° obtained in this work are among the best values reported for conventional RIE technique. The CH4–H2 process is used to etch 1D PhCs with a lattice parameter ranging from 700 to 350 nm and an air filling factor of 0.30 into a 600-nm-thick GaN/sapphire slab. Sharp peaks corresponding to the resonant modes of the nanopatterned structures are observed in the experimental reflection spectra for all the lattice periods. Furthermore, the good optical quality of the nanostructures is evidenced by a resonantly enhanced second-harmonic generation experiment around 400 nm. A second-harmonic generation enhancement factor as high as 105 is obtained, compared with the unpatterned GaN reference slab. These results demonstrate that the CH4–H2 conventional RIE technique is well adapted to the etching of GaN PhC for the fabrication of next generation photonic devices exploiting nonlinear processes.

Selective area growth offers the promise of producing III-nitride photonic crystals (PhCs) without dry etching and concomitant surface damage. Two PhC structures were studied, one comprising an array of flat-topped GaN micropyramids with micrometre-scale periodicity, and the other made up of sharp-tipped pyramids with sub-micrometre periodicity. Angularly resolved reflection and transmission measurements revealed the presence of sharp resonances associated with resonant Bloch modes. As a result, the photonic band structure was determined along symmetry directions of the reciprocal lattice for the two PhC structures.

Si metal oxide semiconductor field effect transistors (MOSFETs) with the gate lengths of 120-300 nm have been studied as room temperature plasma wave detectors of 0.7 THz electromagnetic radiation. In agreement with the plasma wave detection theory, the response was found to depend on the gate length and the gate bias. The obtained values of responsivity (<= 200 V/W) and noise equivalent power (>= 10(-10) W/Hz(0.5)) demonstrate the potential of Si MOSFETs as sensitive detectors of terahertz radiation. (c) 2006 American Institute of Physics.

We have investigated a three-dimensionally periodic (3D) photonic crystal structure based on an epitaxial periodic GaAs/Al0.93Ga0.07As multilayer structure that was designed for non-linear optical interactions. The 3D photonic crystal structure consisted of a two-dimensionally periodic planar photonic crystal hole pattern etched into the one-dimensionally periodic multilayer structure designed for a centre wavelength of lambda = 1.6 µm. Numerical simulations on the 3D PhC structure have shown that it should exhibit slow group velocity modal features near the edge of the photonic bandgap.

We report on the observation of an exalted second-harmonic generation process related to a resonant effect inside a GaN photonic crystal slab. The measured enhancement factor, close to 104, is the highest measured in this photonic crystal slab resonant configuration. This frequency conversion process is also successfully compared to a rigorous modeling using a scattering matrix formalism. In addition, an original polarization study is proposed, leading to an evaluation of the relative contributions of the fundamental and the second-harmonic modes resonances in the second-harmonic response magnitude.

There is a major interest in fabricating III-nitride photonic structures for efficient nonlinear optical processes such as second-harmonic generation because they offer fairly large non linear coefficients and high optical damage thresholds. However, the use of III-nitrides has not been possible practically due to the high dispersion and the small birefringence for phase-matching. Recently, we have shown experimentally the enhancement of second-harmonic generation in epitaxial GaN-based photonic crystals [1]. By using calculated and experimental equifrequency surfaces, it is possible to identify the geometrical configurations that will allow quasi-phase matching to be satisfied and observed experimentally in the available wavelength tuning range of the laser. The second-harmonic field generated has been measured in reflection from the surface of photonic crystals etched into a GaN layer. A very large second-harmonic enhancement is observed when simultaneously the incident beam at the fundamental frequency ω excites a resonant Bloch mode and the second-harmonic field generated is coupled into a resonant Bloch mode at 2ω.