SIMS Investigation of Al Diffusion Across Interfaces in AlGaN/GaN and AlN/GaN Heterostructures

This study investigates Metal–Organic Vapor Phase Epitaxy (MOVPE)-grown AlGaN/GaN and AlN/GaN heterostructures using high-temperature thermal annealing and Secondary Ion Mass Spectrometry (SIMS). By fitting experimental diffusion coefficients (DAl) to the Arrhenius equation, two crucial kinetic parameters were found: the activation energy (Ea) and the pre-factor (D0). In the AlGaN/GaN structure, the dominating out-diffusion of Al has a large D0 = 4.03 × 10−5 cm2 s−1 and a low activation energy in the range of [2.1–2.4 eV]. A substitutional diffusion mechanism in the crystal lattice mediated by defects is closely linked to the low Ea. Significantly higher activation energies (Ea) of 3.66 and 4.59 eV, respectively, control both in- and out-diffusion processes in the AlN/GaN structure. The better intrinsic thermal stability of the pure AlN layer, whose stability is attained by a strong energy barrier, is confirmed by the increase of more than 1.2 eV in Ea.