High-resolution hydrogen profiling in AlGaN/GaN heterostructures grown by different epitaxial methods

Hydrogen (H) incorporation into AlGaN/GaN heterostructures used in high electron mobility transistors, grown by different methods, is studied by high-resolution depth profiling. Samples grown on sapphire and Si(111) substrates by molecular-beam epitaxy and metal-organic vapour phase epitaxy; involving H- free and H- containing precursors, were analysed to evaluate the eventual incorporation of H into the wafer. The amount of H was measured by means of nuclear reaction analysis (NRA) using the H-1(N-15,alpha gamma)C-12 reaction up to a depth of similar to 110 nm into the heterostructures. Interestingly, the H profiles are similar in all the samples analysed, with an increasing H content towards the surface and a negligible H incorporation into the GaN layer ( 0.24 +/- 0.08 at%) or at the AlGaN/GaN interface. Therefore, NRA shows that H uptake is not related to the growth process or technique employed and that H contamination may be due to external sources after growth. The eventual correlation between topographical defects on the AlGaN surface and the H concentration are also discussed.