The authors studied local optical properties of GaAs/AlGaAs heterostructure by scanning tunneling microscope-cathodoluminescence (STM-CL) spectroscopy, where low-energy (similar to 100 eV) electrons field emitted from STM tips were used as bright excitation sources. The STM-CL measurements were performed at the (110) cross-sectional surface of the GaAs/AlGaAs multilayer structure. By evaluating contributions to the spatial resolution from the thermalization and the diffusion of minority carriers (electrons), they found that the field emission electron beam (FEEB) diameter provides the dominant contribution to this spatial resolution of the STM-CL spectroscopy. They also clarified that the difference between the STM-CL measurement position and the STM tip position was caused by the angular deviation of the FEEB from the surface normal.