Fig. 1. (a) Schematic setup of CAFM and four consecutive I−V curves during the scans; (b) typical surface morphology of UV LED grown on a 1° misoriented sapphire substrate; and (c) corresponding current distribution map under forward bias of +7  V.

Fig. 2. (a) Top view SEM image of the surface of UV LED; (b) zoom-in view image near the step edge as indicated by the green box and (c) corresponding ECCI graph.

Fig. 3. (a) Cross-sectional g=[0002] and (b) g=[11−20] dark-field TEM images under two-beam conditions for UV LED grown on a 1° misoriented sapphire substrate; (c) cross-sectional image of the MQW and corresponding Ga EDS mapping near the step edge; (d) zoom-in view of the MQW regions.

Fig. 4. (a) RT PL spectrum of UV LED grown on a 1° misoriented sapphire substrate; (b) PL spectra of UV LED under RT and LT; (c) RT EL spectrum of the same sample under current injection of 200 mA; (d) EL spectra under injection currents ranging from 50 to 300 mA.

Fig. 5. (a) I-V curve; (b) EL spectra under different injection currents from 5 to 80 mA; (c) light output power and estimated EQE as functions of injection current.

Fig. 6. (a) Schematic structure and composition distribution of a UV LED with single QW in the simulation; (b) the distribution of radiative recombination rate; and (c) total current distribution; (d) the energy band structure and (e) distribution of carrier concentration of the flat and inclined active region, respectively. EC and HC stand for electron concentration and hole concentration. (f) EL spectra of the UV LED under different current densities.

Fig. 7. Proposed 3D schematic band diagram of the active region of the UV LED across the step-bunched region.