Multistep In Situ Porosification of N-Polar InGaN with Reduced Hillock Density to Achieve Strain-Relaxed InGaN Pseudosubstrates while Maintaining Miscut Steps

An up to 40% relaxed N-polar InGaN pseudosubstrate was obtained by a multistep in situ porosification technique on the N-polar GaN template using the metal–organic chemical vapor deposition (MOCVD) method. An In_aGa_1–aN/In_bGa_1–bN/GaN superlattice (SL) layer (SL_A) with a higher composition of In_aGa_1–aN (a = 15.2%) compared to In_bGa_1–bN (b = 8.4%) was in situ porosified and coalesced with a thin GaN layer. Following the coalescence layer, an 80 nm-thick In_xGa_1–xN/In_yGa_1–yN/GaN SL (SL_B1) layer with x = 13% and y = 9% was deposited as a second in situ porous layer and coalesced similarly with the GaN layer. Finally, a 160 nm-thick In_xGa_1–xN/In_yGa_1–yN/GaN SL (SL_B2) layer was deposited on top of the SL_B1 and GaN coalescence layer to obtain a strain-relaxed pseudosubstrate. Up to 40% bulk relaxation of the SL_B2 buffer layer was determined after a multistep porosification process. A smooth surface morphology (roughness <2 nm) along with a 50% reduction in hillock density was observed in the partially relaxed InGaN pseudosubstrate (SL_B2). Furthermore, photoluminescence (PL) measurements showed around 80% relaxation for the near-surface SL_B2 layer. The multistep in situ porosification technique demonstrated a robust approach to produce a strain-relaxed InGaN pseudosubstrate suitable for lattice engineering.