Microstructure of AlN Grown on a Nucleation Layer on a Sapphire Substrate

Abstract

The growth conditions and interface microstructure of AlN on sapphire grown using a nucleation layer (NL) have been studied. The AlN layer with NL-AlN grown at 1100 °C exhibits a smooth surface morphology. The epilayer has a small amount of tilting but the twisting is large. For the AlN layer with NL-AlN grown at 1250 °C, the twisting is reduced, but the surface is rough owing to the mixing of crystallographic polarity. The origins of AlN inversion domains are discussed by considering the microstructures observed by transmission electron microscopy (TEM), with the ultimate aim of growing a high-quality AlN layer.

The Influence of V/III and Nucleation Layer on AlN films grown by MOCVD

“…This phenomenon is consistent with that reference [2] has observed. The AlN epilayer grown at high temperature become rough owing to the mixing of crystallographic polarity [2,9] for simple C. Similar to NL on the growth of GaN, the low-temperature NL in AlN plays an important role to relax the strain due to lattice mismatch between AlN and the substrates.…”

“…Due to the unavailability of large area bulk AlN substrates, sapphire and SiC are currently used as substrate materials for the deposition of AlN. However, due to the large differences of lattice mismatch and thermal expansion coefficient between AlN and the substrates, also the small surface mobility of Al adatoms, growth of AlN films still suffers from a smooth surface and a low defect density [2]. Many efforts such as the multi-growth mode modification and pulsed atomic layer epitaxy (PALE) have been made to achieve high crystal quality and smooth AlN films, and great progress has been made [3][4][5].…”

Reduction of dislocation density of aluminium nitride buffer layer grown on sapphire substrate

“…Consequently, it can be inferred that in the annealing process the AlN film undergoes surface reconstruction, whereby the smaller grains in the epilayer merge into bigger ones, providing a smooth surface. This result is similar to the findings of Miyagawa et al, whereby the surface roughness reduces when the annealing temperature is increased from 1200 °C to 1600 °C [23]. Furthermore, this can be proved with the TEM micrographs taken for both annealing temperatures.…”

Annealing of an AlN buffer layer in N2–CO for growth of a high-quality AlN film on sapphire

“…In contrast, the typical FWHM of the (10 12)-plane XRC for an MOVPE-grown AlN layer on sapphire without annealing of the AlN buffer layer is 1000-2000 arcsec, and the density of type-a dislocations is 10 10 cm −2 . 9,21) This result indicates that the dislocations in the AlN buffer layer were annihilated by annealing.…”

“…5,6) To prevent the generation of threading dislocations in the AlN epitaxial layer, the nucleation layer has been controlled. [7][8][9][10][11][12] However, the AlN crystal quality can still be improved by optimizing the nucleation conditions.…”