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 a Ga 1– a N/In b Ga 1– b N/GaN superlattice (SL) layer (SL A ) with a higher composition of In a Ga 1– a N ( a = 15.2%) compared to In b Ga 1– b N ( b = 8.4%) was in situ porosified and coalesced with a thin GaN layer. Following the coalescence layer, an 80 nm-thick In x Ga 1– x N/In y Ga 1– y N/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 x Ga 1– x N/In y Ga 1– y N/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.