Three-dimensional single-crystallite orientation-resolved SHG microscopy of isotropic polycrystalline binary compound semiconductors

Isotropic binary compound semiconductors have been shown to exhibit high optical nonlinearity, which renders them particularly promising for compact optoelectronic and photonic device development through microscale structuring. However, there is a paucity of research tools that provide volumetric imaging of such patterns with high spatial resolution and crystal orientation determination. In this study, the scope of polarization second harmonic generation (SHG) microscopy was expanded to encompass the imaging of single crystalline grains from the deep layers of optically isotropic polycrystalline bulk materials such as chemical vapor deposition zinc selenium (ZnSe). It was demonstrated that focal-plane-localized second harmonic generation can be achieved using a short coherence length and tight focusing, and that grain interfaces provide the majority of the nonlinear signal. The imaging of grain arrangement across a 2 mm-thickness ZnSe sample allowed us to investigate the evolution of spatial resolution with depth provided by a high numerical aperture objective. The developed theoretical approach was used to retrieve the three-dimensional (3D) orientations of individual microcrystallites inside the sample. The present study has expanded the use of the inverse pole figure mapping technique to visualize the crystallographic direction orientations of each grain on the image obtained by polarization SHG microscopy. The demonstrated 3D optical diagnostics method was shown to be a viable investigative tool for isotropic polycrystalline semiconductor materials with a face-centered cubic lattice structure, offering a high spatial resolution and frame rate.