Fig. 1. AFM images and corresponding line profile of the MQWs grown on (a) the 0.2° offcut substrate and (b) the 1° offcut substrate. (c) The FWHM of XRCs and (d) the Raman spectra of the MQWs grown on the 0.2° and 1° offcut substrates.

Fig. 2. EL spectra under the different injection current of (a) the 0.2° and (b) 1° offcut DUV LEDs. (c) The EL spectra at the 20 mA injection condition. (d) I-V curves of the two LEDs. (e) The integral EL intensity as a function of the different injection currents.

Fig. 3. (a) PL spectra of the MQWs grown on the 0.2° and 1° offcut substrates. (b) The integrated PL intensity and (c) emission wavelength mapping of the hexagonal pyramid. The inset OM image shows the hexagonal column and pyramid on the 0.2° offcut sapphire substrate. (d) The IQE values of the two MQWs samples with different laser excitation power.

Fig. 4. (a) SEM image, (b) panchromatic CL intensity mapping, and (c) CL spectra across the steps of the MQWs grown on the 0.2° offcut substrate. (d) SEM image, (e) panchromatic CL intensity mapping, and (f) CL spectra across the steps of MQWs grown on the 1° offcut substrate.

Fig. 5. (a) Schematic diagram of the current direction and step topography. (b) The I-V characters between the n-electrodes in the linear coordinate with error bars and (c) between the n- and p-electrode in the semi-log axis with error bars for both the 0.2° and 1° offcut samples in the two directions.

Fig. 6. (a), (b) Cross-sectional HAADF images and (c), (d) corresponding composition distribution of the Al and Ga elements along the yellow arrow in the HAADF images by the EDS of the AlGaN-based LED grown on the 0.2° and 1° offcut sapphire, respectively.

Fig. 7. 2θ-ω scans of the n-AlGaN layer along the AlN (0002) diffraction.

Fig. 8. (a), (b) Numerical simulation structure and (c), (d) relevant conduction band mapping of AlGaN-based LED grown on 0.2° and 1° offcut sapphire. (e) Band structure along the cutline. (f) Three-dimensional schematic about actual carrier spreading under the influence of potential assisted with step structures.

Fig. 9. (a), (b) I-V characteristics between the n-type and the p-type electrodes in the semi-logarithmic axis under repeated tests for both the 0.2° and 1° offcut samples in two directions, respectively.