Study of impurities diffusion in Al₂O₃/GaN/Al_xGa_1−xN hetero-structures

Abstract

Multilayer GaN/Al_xGa_1−xN structures were grown on a sapphire substrate using metalorganic chemical vapor deposition at atmospheric pressure. The impurities diffusion was studied using secondary ion mass spectrometry. The Al profile at AlGaN/GaN interface showed different broadening degrees depending on the AlGaN layer stoichiometric and the distance from the substrate. By increasing the trimethylgallium flow rate when growing the AlGaN layer, it was found that the Al diffusion (D_Al) coefficient toward the GaN layer decreases from 1.2 × 10^–14 to 1.8 × 10^–15 cm²/s. The highest D_Al was obtained at the GaN/Al_xGa_1−xN interface, the closer one to the GaN/sapphire substrate. The distribution profiles of Ga, Al and O near GaN/Al₂O₃ upon thermal annealing under nitrogen were measured in the temperature range 1000–1120 °C. A deep penetrating O diffusion tail from sapphire into GaN was observed. The interstitial O diffusion coefficient (D_O) was found to be $D_{0} = 7.6 \times 10^{ - 10} \exp \left( {\frac{ - 1.24 eV}{{k_{{\text{B}}} T}}} \right)$ while the Al substitutional diffusion was found to be $D_{{{\text{Al}}}} = 5.4 \times 10^{ - 8} \exp \left( {\frac{ - 2.8 eV}{{k_{{\text{B}}} T}}} \right)$.