Assessment of refractive index changes by spectral reflectance in the first stages of AlxGa1−xN layer growth using SiN treatment

Correlation of structural and optical properties of AlGaN films grown on SiN-treated sapphire by MOVPE

“…In the first stage of the AlGaN growth on sapphire substrate (Group A), the dislocation density is high near the sapphire interface, due to the 3D growth mode. When the growth is continued, i.e., the AlGaN thickness is further increased, a transition from 3D to 2D growth mode is occurred, as observed from SEM images [29] and in situ reflectivity (Fig. 2a).…”

“…Another explanation of the increase in the O signal is associated with the possibility of the oxidation of the AlGaN surface by O atoms from the ambient air. However, the SEM image of sample A4 [29], excludes this hypothesis; it presents a terrace-like surface morphology without any oxidation symptoms. From the results obtained from SIMS investigation, we conclude that Al vacancy with oxygen impurity in nitrogen-vacancy complex (V Al -O N ) could be the primary origin of the degeneration in the PL decay response.…”

“…Consequently, the dislocation density decreases as the coalescence of adjacent grains occurs and as the sapphire interface region becomes far. The decrease in the dislocation density could also be attributed to the increase of the interdependence parameter during the transition from 3D to 2D growth mode [29]. In fact, the rise of the interdependence parameter, which reflects the interaction between tilt and twist mosaic (edge and screw dislocations), leads to a decrease in both edge and screw dislocation densities.…”

“…The different growth steps have been described in Refs. [26,28,29], where the correlation between the reflectivity signal evolution and surface morphology obtained from atomic force microscopy (AFM) and scanning electronic microscopy (SEM) has been analyzed and demonstrated. In particular, the morphology of the studied AlGaN layers evolves from a surface covered with discontinued islands to a smooth continued surface, i.e., the transition from 3D to 2D growth mode occurs when the AlGaN (GaN template) thickness increases.…”

“…Although many reports have been published on the study of the layer thickness effect on the structural and optical properties of AlGaN-related heterostructures [24,26,28,29], some fundamental properties are still unexplored for such heterostructures, such as the evolution of the internal electric field and the carrier decay times with AlGaN (or GaN-template) thickness. In fact, due to the presence of charged defects (dislocation, impurities, and point defects) and polarization charges (spontaneous and piezoelectric), a huge internal electric field exists along (0001) direction of hexagonal AlGaN heterostructures [18,30,31].…”