Characterization of anti-phase boundaries in hetero-epitaxial polar-on-nonpolar semiconductor films by optical second-harmonic generation

摘要

Compound semiconductor layers (e.g., GaAs) grown on elemental semiconductor substrates (e.g., Si, Ge) are vulnerable to formation of anti-phase boundary (APB) defects. We show that optical second-harmonic generation (SHG) signals from APB-rich epi-layers are orders of magnitude weaker than from APB-free samples. Moreover, scanning SHG images of APB-rich layers reveal microstructure lacking in APB-free layers. We attribute these findings to the sign reversal of the second-order nonlinear optical susceptibility X_(ijk)~((2)) between neighbouring anti-phase domains within the incident laser spot. In contrast, SHG is insensitive to threading dislocations. Thus, SHG can identify APBs selectively and non-invasively for advanced MOSFET device applications.