ULTRA-WIDEBAND VIVALDI ANTENNA ARRAYS WITH TEM HORN

The paper presents the results of experimental studies of the processes of formation of holes by themethod of focused ion beams on GaAs(111) substrates and their subsequent transformation during annealingin an ultrahigh vacuum chamber of molecular beam epitaxy in an arsenic flux and in its absence.It was found that at an ion beam exposure time of 1 ms, the processes of ion accumulation in the substrateprevail over the processes of the material sputtering, whereas at an exposure time of 5 ms, intensive sputteringof the substrate material occurs at the points of exposure to the ion beam with an increase in thedepth of the etched areas with an increase in the number of ion beam passes. After annealing of substrateswith ion beam-modified areas, the holes increase significantly in size as a result of local droplet etchingprocesses. Studies showed that the hole size after annealing in the arsenic flux exceeds the hole size afterannealing in the absence of an arsenic flux in almost the entire range of the number of ion beam passes.The dependences of the depth and lateral size of the holes on the number of ion beam passes are nonmonotonic,due to the competition of the processes of droplet etching and crystallization of ion beammodifiedareas in the arsenic flux. The results of experimental studies show that to obtain highly symmetricpyramidal holes with low surface density, it is required to create on the GaAs(111) surface an array offocused ion beam treatment points with an interval of 2 μm at an exposure time of 5 ms and a number ofpasses equal to 40. At the next stage, it is necessary to transform the ion beam processing points into pyramidal-shaped holes by annealing the substrate in a molecular beam epitaxy chamber at a temperatureof 600°C and a time interval of 60 minutes. The technique proposed in this work, based on the combinationof ion-beam surface treatment and molecular beam epitaxy, makes it possible to obtain nanoholeswith the required symmetry, which can further serve as nucleation centers for InAs quantum dots with thedesired properties.