Direct measurement of photoluminescence spatial distribution near the GaAs/AlGaAs quantum well edge using a scanning near-field optical microscope

Spatial distribution of photoluminescence (PL) from quantum well semiconductor structures was studied. The structures containing active layer of GaAs (10 nm) surrounded with 25 nm Al0.42Ga0.58As barrier layers were grown by MBE on GaAs substrate. The wet etching process was used to prepare wire structures of the active layer with different wire width. The scanning near-field optical microscope (SNOM) with shear-force feedback was used to scan the surface topography with simultaneous spectra storage for each surface point. The tapered optical fiber with Al-coated tip (aperture size less than 0.3–0.4 μm) was used. The tip was used both for the sample illumination and PL light collection. A liquid-nitrogen-cooled CCD-camera was used to detect the spectra. PL spectrum evolution across the wires direction was stored. The 1hh–le band peak in PL spectrum can be clearly seen with maximal intensity in the middle of the wire. The carrier diffusion model with the same model parameters for all structure sizes can quantitatively describe the obtained distribution of PL signal. We have assumed in the model that there is a dead region at the sidewalls. The diffusion length remains the only fitting parameter of the model, and the best fit values were found.