Cathodoluminescence hyper-spectral imaging of InGaN/GaN quantum wells

Cathodoluminescence (CL) spectroscopy is a powerful tool for investigation of light-emitting semiconductors. A field-emission gun SEM has been used to study the CL of InGaN/GaN quantum wells (QWs) with high spatial resolution approaching 10 nm. Forming a hyper-spectral image by collecting CL spectra at each pixel within a 2D map allows observable surface features to be correlated to observed changes in CL spectra. Comparison is made to photoluminescence measurements as a function of temperature down to 16 K. InGaN/GaN QWs were grown on c-plane sapphire substrates by MOCVD, emitting in the blue and green. To improve crystal quality a high-temperature AlN buffer layer technology was applied. SEM imaging revealed the well-known V-shaped pits in addition to trench-like features. CL spectral mapping showed shifts of the emission energy as well as changes in the line shape of spectra from those features. The non-uniformity of the emission of the QW is strongly influenced by the surface morphology and is related to local variations in dislocations, composition or strain. High spatial resolution CL provides useful information on the material properties and performance on a sub-micron scale.