The structural characteristics of radiation damage produced by high energy (2.7 MeV) ion implantation in GaAs

Abstract

The radiation damage induced by the implantation of 2.7 MeV P⁺ and N⁺ ions with a dose of 6.4 × 10¹⁶ ions cm⁻³ into GaAs at room temperature has been studied by transmission electron microscopy. The as-implanted material was found to consist of a buried amorphous layer which was sandwiched between a heavily damaged but crystalline cover layer exhibiting a high density of black dot defects, microtwins and dislocation loops and a less damaged substrate region. Post-implantation annealing of the specimens at 250° C for 6 h resulted in the recrystallization of the amorphous and cover layers by random nucleation of grains producing a polycrystalline region on the single crystal substrate. However, a second stage annealing of these samples at 400° C for 2 h caused an epitaxial regrowth of the implanted layer on the undamaged substrate producing single crystal regions which were heavily twinned on all {111} planes. The results of the present microstructural analyses have been compared with the previous infra-red reflectivity studies on identically implanted GaAs samples to determine the effects of structural changes on the dielectric properties. The two studies are found to be in reasonable agreement. The present results are also compared with those from previous lower energy-lower dose implantations.