Fig. 1. (a) Schematic structure and (b) wafer temperature and the corresponding surface reflectivity of multi-layer in situ treated AlN. (c) Mirror-like and crack-free in situ treated AlN surface. (d) AFM images of in situ and ex situ treated AlN. (e) Pole figure of AlN (112¯2), (0002), and sapphire (022¯4) plane diffractions. (f) FWHM of XRC diffraction of AlN templates as a function of azimuth angles.

Fig. 2. (a) ADF images of in situ treated AlN template taken along [11¯00] and [112¯3] zone axes. (b) Optical transmission spectra and (c) Raman spectra of in situ and ex situ treated AlN templates.

Fig. 3. (112¯2) symmetric RSM of semipolar DUV LEDs grown on in situ and ex situ treated AlN templates measured along (a) ⟨112¯3⟩ and (b) ⟨11¯00⟩ directions. (c) (112¯4) asymmetric RSM of semipolar DUV LEDs on in situ and ex situ treated AlN templates. (d) Adjusted (112¯4) peak positions of asymmetric RSM according to the different tilt angle of each layer.

Fig. 4. Overall and enlarged ADF images of DUV LEDs on the in situ treated AlN template along (a) [11¯00] and (b) [112¯3] zone axes. ADF images of DUV LEDs on the ex situ annealed AlN template and the corresponding enlarged images of defects around the interface along (c) [11¯00] and (d) [112¯3] zone axes. (e) Schematic of the transformation of three types of defects, DI, DII, and DIII, in AlN and AlGaN layers. (f) PL spectra of DUV LEDs on different AlN templates.

Fig. 5. High-resolution TEM images of (a) as-grown and (b) HTA-treated AlN films. (c) Ideal AlN and (d), (e) distorted AlN after high-temperature annealing. (f) Radial distribution function of N atoms around an Al atom by high-temperature annealing.