Development of Photoluminescence Microscope with Sub-Micron Resolution at Low Temperature and Its Application to Detection of Defects in Wide-Gap Semiconductors
Masahiro YOSHIMOTO
Abstract:A new photoluminescence (PL) microscope has been developed with a conventional optical system to obtain a monochromated PL image at a low temperature with a spatial resolution in sub-micron range. The objective and sample were put in the identical vacuum chamber to ensure thermal insulation between them. The spatial resolution at 15 K was confirmed to be almost equal to the diffraction limit, i.e., 0.3 ƒÊm, at a wavelength of 488 nm. The microscope clearly visualized defective region, and polytype domain with a spatial resolution of 0.3 ƒÊm in GaN. PL emissions ascribed to free excitons (EXA) and excitons bound to donors (D0X) were discriminated in ƒÊ-PL measurements at 15 K on epitaxially laterally overgrown (ELO) GaN. The emission at 3.487 eV ascribed to D0X became strong above the SiO2 mask within a distance of 8 ƒÊm from the mask. In a ƒÊ-PL image related to excitons bound to N atoms in a 4H-SiC homoepitaxial layer, a dark line was observed at a line-shaped surface defect. Since the PL emission from donor(N)-acceptor(B) pairs was spatially uniform, N atoms were incorporated uniformly in the 4H-SiC epilayer. The dark line is probably caused by an enhancement of nonradiative recombination at the surface defect. Key Words:Microscopic photoluminescence, GaN, Sic, Sub-micron spatial resolution, Low temperature, Defect, Auto-doping, Polytype