Cross sectional evaluation of boron doping and defect distribution in homoepitaxial diamond layers



In some diamond-based semiconducting devices, large variations of doping level are required over short distances. Tools to determine doping level and defects distribution should therefore be developed. The present contribution shows the capabilities of electron microscopy in this field. Focused ion beam (FIB-dual beam) cross section preparations allowed evaluating doping level in highly boron doped sample with doping transition down to some nm by diffraction contrast mode of transmission electron microscopy (CTEM) and by high angle annular dark field mode of scanning transmission electron microscopy (HAADF-STEM). The sensibility of the latter is around 1019cm-3 and, thus, cathodoluminescence (CL) is required for lower doping levels. Cross sectional analysis on FIB prepared lamella allowed to separate the epilayer behaviour from that of the substrate. Mid-gap centers involving boron, hydrogen and, for some peaks, also nitrogen are revealed. sp2 bonds are also present in the grown epilayer. These transitions make difficult the observation of excitonic recombinations in the cross section configuration. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)