Fig. 1. (a), (d) SEM images of 4H- and 6H-SiC single root forest-like NWs. The insets show their diameter distributions. (b), (e) AFM images of 4H- and 6H-SiC NWs as well as height distributions along denoted lines. The insets show their diameter distributions. (c), (f) XRD patterns of the 4H- and 6H-SiC single crystals and NWs. The black bars indicate the standard XRD patterns of bulk crystals. (g) Side-view SEM image of 4H-SiC forest-like NWs with a cavity structure. (h) Schematic diagram showing laser irradiation onto the SiC NW array.

Fig. 2. Cavity-mode PL spectra of (a), (b) 4H-SiC NWs [spots in (e)] and (c), (d) 6H-SiC NWs [spots in (f)] under 532 nm laser (202.8μW) excitation. (e), (f) Corresponding optical microscope graphs. (g) Scatter plots corresponding to the split PL peaks at the denoted sites. The optical paths derived based on the energy difference of adjacent peaks are shown.

Fig. 3. (a), (b) High-resolution TEM images of two 4H-SiC NWs. (c) HAADF and EDS element mapping images of a single 4H-SiC NW.

Fig. 4. 2D contour temperature-dependent PL spectra (excitation: 325 nm) of (a) 4H-SiC NWs and (d) 6H-SiC NWs. Plot of the PL peak wavelength and intensity versus temperature for (b), (c) 4H-SiC NWs and (e), (f) 6H-SiC NWs.

Fig. 5. Time-resolved PL spectra (excitation: 400 nm, emission: 576 nm) of the 4H-SiC NW forest in the Fabry–Pérot cavity excited under an intense femtosecond laser, and that of the exposed free-space 4H-SiC NW forest excited under a weak NanoLED light.

Fig. 6. KPFM CPD maps of (a) 4H-SiC NWs and (b) 6H-SiC NWs and (c) corresponding CPD distributions. (d), (e) UPS spectra of 4H- and 6H-SiC NWs and (f) corresponding energy band diagrams with denoted UPS-derived work function as well as VBM and conduction band minimum (CBM).