Spectroscopic imaging of InGaN epilayers

We review several spectroscopic imaging techniques, with progressively high er spatial resolution, applied to InGaN epilayers and quantum wells (QW). T he techniques discussed are: photoluminescence (PL) mapping, confocal laser scanning spectroscopy, and cathodoluminescence imaging. PL mapping (via po int-by-point PL spectroscopy) is necessary when samples show macroscopic in homogeneity. Confocal microscopy uses a diffraction-limited laser spot to a ddress a sample in a raster scan. Here we report, for the first time, obser vations, on a microscopic scale, of spectroscopic fine structure in InGaN l ayers of moderate indium content. Cathodoluminescence (CL) imaging provides a vast amount of information on thin semiconductor layers that are well-ma tched to the penetration profile of electron beams of modest energies (from approximate to 1 to 60 keV). Panchromatic images provide useful informatio n when compared with corresponding structural images produced by electron s cattering in the sanning electron microscope (SEM). Application of image pr ocessing techniques to such images reveal striking correspondences on a siz e-scale below one micron.