On the interpretation of cathodoluminescence intensity maps of wide band gap nanowires

Abstract

It is commonly assumed in the spatially resolved cathodoluminescence (CL) studies of wide band gap (WBG) nanowires (NWs) that the CL intensity maps of deep-level (DL) and near band edge (NBE) emission reflect the spatial distribution of defects in these structures. On this basis, crucial conclusions about the technological growth conditions of NWs are drawn. However, here we showed using three-dimensional finite element analysis that in the case of WBG NWs, which exhibit surface band bending, the CL intensity maps of DL and NBE emission do not reflect the distribution of defects but, instead, the electric field strength in NWs. In particular, we found that independently of the defect concentration distribution, the DL emission intensity is always the highest in the areas where the electric field is the strongest and the lowest where the electric field is absent, while the NBE emission intensity exhibits the opposite trends. We explained this finding by the strong influence of the electric field on the spatial distribution of radiative recombination rates. Overall, our results indicate that (i) the frequently observed spatially inhomogeneous CL intensity distribution in WBG NWs can result from the presence of electric fields but not, as widely accepted, non-uniform defect distribution and (ii) spatially resolved CL spectroscopy measurements on the WBG NWs in most cases can not provide any quantitative information about the DL defect distribution.