We investigated AlGaN layers grown by metalorganic chemical vapor deposition (MOCVD) on high temperature
(HT-)GaN and AlGaN buffer layers. On GaN buffer layer, there are a lot of surface cracking because of tensile strain in
subsequent AlGaN epilayers. On HT-AlGaN buffer layer, not only cracks but also high densities rounded pits present,
which is related to the high density of coalescence boundaries in HT-AlGaN growth process.
The insertion of interlayer (IL) between AlGaN and the GaN pseudosubstrate can not only avoid cracking by modifying
the strain status of the epilayer structure, but also improved Al incorporation efficiency and lead to phase-separation.
And we also found the growth temperature of IL is a critical parameter for crystalline quality of subsequent AlGaN
epilayer. Low temperature (LT-) AlN IL lead to a inferior quality in subsequent AlGaN epilayers.