Optical second harmonic imaging: a versatile tool to investigate semiconductor surfaces and interfaces

Abstract

Optical second harmonic (SH) imaging using femtosecond laser pulses (782 nm, 80fs) is applied to investigate the structural quality of SiC and ZnO thin films grown by chemical vapour deposition (CVD) on Si(100) substrates. We find a spatially uniform SH response from the SiC sample as well as a regular 4-fold symmetry (3C-SiC-(001)) in the rotational SH anisotropy. The ZnO film is poly-crystalline as indicated by a strongly position dependent SH response and the missing regularity in the rotational SH anisotropy. The estimated grain size is ∼ 30-50 μm. Furthermore our time dependent SHG measurements on native Si/SiO 2 for laser peak intensities up to 100 GW/cm 2 indicate that hole injection and trapping into the ultrathin SiO 2 layer contributes to the SH signal above > 45 GW/cm 2 . The SHG images of defects irreversibly induced in Si/SiO 2 under laser irradiation are reproduced by scanning electron microscopy (SEM).