Sub-μm scale photoluminescence images of wide bandgap semiconductors by cryogenic scanning optical microscope

Photoluminescence images with a sub-μm spatial resolution were obtained at 15 K using a newly developed cryogenic scanning microscope with both high throughput and simplicity of measurement procedure. The objective was put in a sample chamber to reduce thermal conduction from the objective to the sample. The spatial resolution at 15 K was measured to be 300 nm at a wavelength of 488 nm, which is almost equal to the diffraction limit. The microscope demonstrated μm-scale defective regions emitting a PL signal at 3.40 eV in GaN grown on SiC. At an elongated surface defect in a 4H–SiC homoepitaxial layer, the PL image ascribed to excitons bound to neutral nitrogen atoms showed a dark line coincident with the defect, indicating that non-radiative recombination dominates over the excitonic emission at the surface defect.