Raman mapping images of GaN buffer layer grown on CGH: (a) radial breathing mode (RBM) of CNT and (b) A1 (LO) mode of GaN. (c) Combination of Raman mapping images shown in Figs. 2(a) and (b). Green parts correspond to A1 (LO) mode of GaN while red parts are associated with RBM of CNTs. The overlapped area of RBM and A1 (LO) mode are shown in yellow. (d) Raman spectra obtained from regions marked by A and B of Fig. 2(c).