Fig. 1. (a) Epitaxial structure of the scribed via holes and porous layer. (b) Cross-sectional view of the nanoporous n-AlGaN layer etched at 40 V. (c) SEM image of the cleaved region in the porous layer showing the subwavelength grating structure at higher magnification.

Fig. 2. (a) PL spectra of samples with different EC etching voltages. (b) Corrected PL enhancement ratio and average size of pore versus EC etching voltage.

Fig. 3. (a) Raman spectra of the etched samples and the reference sample measured at RT. (b) Raman shift (left) and PL peak wavelength (right) as a function of etching voltages.

Fig. 4. (a) Schematic diagram of the angular-dependent polarization PL measurement. (b) Far-field PL distribution in polar coordinates. (c) Enhancement ratio of samples etched at 60 V and 80 V as a function of θ.

Fig. 5. Angular-dependent PL intensity profile in the (a) TE and (b) TM mode; (c) the side-emitting PL spectra at different polarization angles: ψ=0°, ψ=90°, when θ=60°; (d) the integrated PL intensity against polarization angle ψ=0°–360° of the reference unetched sample and 80 V etched sample, respectively.

Fig. 6. EL spectra and normalized EQE versus current of (a), (c) the 80 V etched sample compared to (b), (d) the reference sample. The inset of (a) shows the schematic of the porous LED.