Probing local emission properties in InGaN/GaN quantum wells by scanning tunneling luminescence microscopy

Scanning tunneling electroluminescence microscopy is performed on a 3-nm-thick InGaN/GaN quantum well with x = 0.23 such that the main light emission occurs in the green. The technique is used to map the local recombination properties at a scale of ~10 nm and to correlate them with the surface topography imaged by scanning tunneling microscopy. A 500 nm x 500 nm area around a 150-nm large and 2.5-nm deep hexagonal defect is probed, revealing emission at higher energies close to the defect edges, a feature which is not visible in the macro-photoluminescence spectrum of the sample. Via a fitting of the local tunneling electroluminescence spectra, quantitative information on the fluctuations of the intensity, energy, width and phonon replica intensity of the different spectral contributions are obtained, revealing information about carrier localization in the quantum well. This procedure also indicates that carrier diffusion length on the probed part of the quantum well is approximately 40 nm.