New conditions for one-step ELO were implemented to grow coalesced (1120) non-polar and (1122) semi-polar GaN layers starting, respectively, from Rand M-plane sapphire. A great part of the stacking faults (SFs) and dislocations are filtrated resulting in GaN material with better structural and optical properties. In the ELO-like (1120) and (1122) films, the near band edge emission dominates photoluminescence spectra and is in the range 3.45 -3.48 eV depending on lattice deformation. The strongest emission is met for the semi-polar (1122) ELO. When mask stripes are not normal to the c-axis, a singular ELO is developed with inclined coalescence facets. However, in this case, SFs overgrow above the mask and so lead to poor optical properties, dominated by SF and dislocation related peaks. In any case, the internal electric field reduction in (Al,Ga)N/GaN non-or semi-polar quantum-wells stacks is better viewed when the heterostructures are grown on ELO with stripes normal to the c-axis.
OriginalPaper way to improve the microstructure is by filtrating most of these extended defects via the use of epitaxial lateral overgrowth (ELO) techniques [8][9][10]. In this paper we review our study on the MOVPE epitaxy optimisation and on the microstructure and optical improvements of (1120) a-plane and (1122)-plane semipolar GaN layers using a one-step ELO technique. The consequence on polarisation in (Al,Ga)N/GaN MQWs structures is then presented.
We report highly efficient four wave mixing in a GaInP photonic crystal waveguide. Owing to its large bandgap, the ultrafast Kerr nonlinearity of GaInP is not diminished by two photon absorption and related carrier effects for photons in the 1550 nm range. A four-wave-mixing efficiency of -49 dB was demonstrated for cw pump and probe signals in the milliwatt range, while for pulsed pumps with a peak power of 25 mW the conversion efficiency increased to -36 dB. Measured conversion efficiency dependencies on pump probe detuning and on pump power are in excellent agreement with a simple analytical model from which the nonlinear parameter gamma is extracted. Gamma scales approximately with the square of the slow down factor and varies from 800 W(-1) m(-1) at a pump wavelength lambda(p)=1532 nm to 2900 W(-1) m(-1) at lambda(p)=1550 nm. These values are consistent with those obtained from self phase modulation experiments in similar devices.
We describe nonlinear properties of a GaInP photonic crystal Fabry-Perot resonator containing integrated reflectors. The device exhibits an extremely large static nonlinearity due to a thermal effect. Dynamical measurements were used to discriminate between the thermal and Kerr contributions to the nonlinearity. The high frequency nonlinear response is strictly due to the Kerr effect and the efficiency is similar to that obtained in self-phase modulation and four wave mixing experiments. The waveguide dispersion and the wavelength dependent integrated reflectors yield a series of transmission peaks with varying widths which determine the maximum speed at which the device can operate. Switching and wavelength conversion experiments with 92ps and 30ps wide pulses were demonstrated using pulse energies of a few pJ. The switching process is Kerr dominated with the fundamental response being essentially instantaneous so that the obtainable switching speed is strictly determined by the resonator structure.
We present site-controlled low density InAs quantum dots grown by molecular beam epitaxy with a template based overgrowth technique allowing enlarged buffer layers upto 55 nm. Growing a seeding layer of InAs quantum dots in etched holes reduces closing of the holes, so that a second layer of InAs quantum dots can be aligned to the holes after a buffer layer overgrowth. Confocal microphotoluminescence measurements show a significant decrease of the low temperature photoluminescence linewidth of the quantum dots to an average value of ∼500 μeV and a minimum width of 460 μeV. This is to be compared to 2 to 4 meV of quantum dots grown on thin buffer layers. This improvement is due to the enlarged distance to residual defects at the overgrown surface.
We investigate four-wave mixing (FWM) in GaInP 1.5 mm long dispersion engineered photonic crystal waveguides. We demonstrate an 11 nm FWM bandwidth in the CW mode and a conversion efficiency of -24 dB in the quasi-CW mode. For picosecond pump and probe pulses, we report a 3 dB parametric gain and nearly a -5 dB conversion efficiency at watt-level peak pump powers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.