Effect of Focused Ion Beam Imaging on the Crystallinity of InAs

We investigated the effect of focused ion beam (FIB) imaging on the crystallinity of InAs using Raman scattering. A spatial correlation model was used to fit the broad band induced by FIB imaging. The fitting gives a correlation length of ~42 A for the noisiest image condition (with an ion fluence of 7.4×1010 cm-2), implying severe damage in the surface layer of InAs. However, further increasing the fluence by several orders of magnitude only decreases the correlation length from 42 to 35 A. We attribute the severe damage to the high beam current density and the low scanning speed of the FIB imaging process. These process conditions, along with low InAs thermal conductivity, also leads to a high local temperature in the exposed region that largely annihilated the defects and resulted in the nearly fluence-independent behavior.