Optical Imaging of Defect Density Distribution in Ion-Implanted GaAs using Ultrafast Carrier Dynamics

By combining time-resolved pump-probe reflectivity measurements with scanning laser microscopy, we demonstrate microscopic two-dimensional (2D) imaging of defect density distribution on a GaAs surface. The carrier lifetime is significantly reduced by the recombination process through defect states introduced by 5-keV He⁺ ion implantation. Thus, when plotting the probe beam reflectivity at 1 ps after photoexcitation and scanning the probe beam across the GaAs surface at a spatial resolution of 2 μm with a scanning step of 10 μm, we obtain a clear image of defect distribution corresponding to a mask edge pattern placed on the sample during ion implantation. Clearer images can be obtained using longer wavelength probe light.