A microstructural comparison of the initial growth of AlN and GaN layers on basal plane sapphire and sic substrates by low pressure metalorganic chemical vapor deposition

In-situ reflectance monitoring during MOCVD of AlGaN

“…Wickenden et al 20 observed that the degree of crystallinity of the GaN LT buffer increases during the temperature ramp and anneal. George et al 21 and Wu et al 22 employed transmission electron microscopy (TEM) and atomic force microscopy (AFM) to examine the as-deposited and thermally annealed LT buffer layers. Qualitatively, the two reports made similar observations that the average grain size and RMS roughness of the GaN buffer layers increased at the end of the ramp/anneal.…”

The properties of annealed AlN films deposited by pulsed laser deposition

“…Stress relief is more likely to occur in films grown on sapphire, because the strain is larger and the interface bonds are weaker than they are for films grown on SiC. In their growth studies of AlN on SiC and sapphire George et al 34 also found that bonding across the interface appeared quite different for the two substrates. The excellent single crystalline nature of this AlN film in which the stress has been partially relieved is striking, so it could be a candidate for a compliant substrate.…”

Mushroom structure of GaN template for epitaxial growth of GaN

“…In the commercial MOCVD growth process, before growth of HT GaN epitaxial layers, the buffer layer is ramped to a high temperature (ramp anneal) and held at the high temperature for some period of time (HT anneal) with the Ga source off [27,[31][32][33]. These two anneals are included in the so-called recrystallization step [27,[31][32][33]. The previous studies [27,[31][32][33] reported the morphological evolution of the buffer layer after the recrystallization step.…”

“…These two anneals are included in the so-called recrystallization step [27,[31][32][33]. The previous studies [27,[31][32][33] reported the morphological evolution of the buffer layer after the recrystallization step. We believe that, since the recrystallization step included the HT anneal, those studies might have missed the mushroom formation.…”

“…4 seems connected to the question of why such a mushroom structure was not observed in the literature. In the commercial MOCVD growth process, before growth of HT GaN epitaxial layers, the buffer layer is ramped to a high temperature (ramp anneal) and held at the high temperature for some period of time (HT anneal) with the Ga source off [27,[31][32][33]. These two anneals are included in the so-called recrystallization step [27,[31][32][33].…”