Fig. 1. (Color online) The effect of differentT_A on theρ and ΔV of Hall samples.

Fig. 2. (Color online) (a) TypicalI–V curve, (b)ρ and p, (c) R_sh andμ results for p-GaN samples. (d) TypicalI–V curve, (e)ρ and p, (f) R_sh andμ results of p-AlGaN/GaN SLs samples.

Fig. 3. (Color online) Schematic of step etching experiment, etching damage is also considered.

Fig. 4. (Color online) Measuredd_Eby AFM for differentetching time.

Fig. 5. (Color online) (a) Measured Mg & hole concentration for p-AlGaN/GaN SLs sample. The red broken line shows the equivalent doping profile used in the Hall measurements. (b) Analyzed Mg & hole concentration near the surface region for the same sample. The orange broken line shows the equivalent hole profile with a constant density.

Fig. 6. (Color online) (a) Fitting ofd_NC with differentd_E. (b) Band diagram near the fresh surface. (c) Band diagram near the etched surface when contact layers are completely removed. (d) MeasuredR_sh plotted againstd_C.

Fig. 7. (Color online) The 2theta/omega scan of p-AlGaN/GaN SLs by HR-XRD (Bruker D8 Discover).

Fig. 8. (Color online) Electrical properties of p-AlGaN/GaN SLs (circles) and p-GaN (squares) samples before and after ICP etching. Solid and broken lines are the average value before etching for p-AlGaN and p-GaN, respectively.