Observation of insulating nanoislands in ferromagnetic GaMnAs

Abstract

Resonant Raman data on ferromagnetic GaMnAs reveal the existence of a new kind of defect: insulating nanoislands consisting of substitutional Mn-Ga acceptors surrounded by interstitial Mn-I donors. As indicated by the observation of a sharp 1S(3/2)-> 2S(3/2) Raman transition at similar to 703 cm(-1), the acceptor-bound holes inside the islands are isolated from the metallic surroundings. Instead, Mn-bound excitons do couple to the ferromagnetic environment, as shown by the presence of associated Raman magnon side bands. This leads to an estimate of 5-10 nm for the nanoisland radius. The islands disappear after annealing due to the removal of the Mn-I ions.