  We demonstrate monolithic aluminum gallium arsenide (AlGaAs) optical
anoantennas. Using a selective oxidation technique, we fabricate such epitaxial
semiconductor nanoparticles on an aluminum oxide substrate. Second harmonic
generation from an AlGaAs nanocylinder of height h=400 nm and varying radius
pumped with femtosecond pulses delivered at 1554-nm wavelength has been
measured, revealing a peak conversion efficiency exceeding 10-5 for
nanocylinders with an otpimized geometry.
