Microscopic mapping of infrared modulated photoluminescence spectra with a spatial resolution of ∼2 μm

Infrared photoluminescence (PL) spectroscopy with micron-scale spatial resolution is essential for the optoelectronic characterization of narrow-gap microstructures and single defects, yet it poses significant challenges due to the exceedingly weak PL signal and strong background thermal emission. This work introduces an infrared micro-PL (μPL) mapping system that achieves a spatial resolution of ∼2 μm, leveraging the inherent advantages of the step-scan Fourier transform infrared spectrometer-based modulated PL technique in the mid- and far-infrared regions. The configuration of the experimental system is described, and a theoretical upper limit of spatial resolution is derived to be about 1.53 μm. A typical application of the μPL spectral mapping system is demonstrated on a mid-infrared InAs/GaSb superlattice that had undergone surface dry-etching for focal plane array fabrication. Successful identification of grooves is accomplished in both spectral energy and integral intensity images derived from the μPL spectral mapping. An actual spatial resolution of ∼2.34 μm remains for the μPL spectral mapping, even though the diffusion of photo-generated carriers is present in the InAs/GaSb superlattice. The results demonstrate the feasibility of the infrared modulated μPL spectral mapping with a significantly enhanced spatial resolution of about 2 μm and an extended functional wavelength range of 2.5-22 μm, which may serve as an effective vehicle for characterizing the microstructures of narrow-gap semiconductors.