The work by our PhD student Maruf Sarkar has been chosen as cover image for the latest volume of the Microscopy and Microanalysis journal.
The sub-surface image of a porous GaN distributed Bragg reflector (DBR) has been captured by backscattered electron scanning electron microscopy (BSE-SEM). The DBR is fabricated by epitaxy of undoped and highly Si-doped GaN pairs followed by doping-selective electrochemical etch-ing. Here, a Zeiss GeminiSEM 300 operating at a 20 keV landing energy enables non-destructive characterization. By imaging through the 45 nm GaN cap, BSE-SEM reveals the morphology of the first porous layer, 45 nm to 108 nm sub-surface. The contrast relates to material density: high-density (white, GaN), medium-density (grey, sub-surface pores), and low-density (black, open volumes at threading dislocation cores). In such DBRs, BSE-SEM images the same branching pores and Voronoi-like domains as scanning transmission electron microscopy. For further details see the manuscript by Maruf Sarkar et al on the journal website (link).
