Surface treatments on AlGaN/GaN heterostructures for gate dielectric Al2O3 thin films grown by Atomic Layer Deposition

A systematic study was performed on the effects of surface treatments before Atomic Layer Deposition (ALD) growth of Al2O3 thin films on (0001)AlGaN/GaN substrate. The AlGaN/GaN surface was treated either with: H2O2:H2SO4 (A treatment) and H2O2:H2SO4+H2O:HF (B treatment). After surface wet-treatments, Al2O3 was immediately deposited at 250 °C by Plasma Enhanced ALD from trimethylaluminum precursor. The film thicknesswasmeasured to be about 27 nm using transmission electronmicroscopy and different structural evolution was observed under electron beam analysis, re-arranging from amorphous as-deposited films to polycrystalline or epitaxial films depending on the pre-deposition treatment. Surface morphology obtained by atomic force microscopy in tappingmode showed smooth Al2O3 layerswith lower roughness in the case of films deposited after B treatment. Dielectric properties have been evaluated for films deposited after both A and B treatments and better dielectric properties have been observed for film fabricated after B treatment. Moreover, dielectric properties improved after post-deposition annealing at high temperature.