Cubic Crystalline Erbium Oxide Growth on GaN(0001) by Atomic Layer Deposition

Growth of crystalline Er₂O₃, a rare earth sesquioxide, on GaN(0001) is described. Ex situ HCl and NH₄OH solutions and an in situ N₂ plasma are used to remove impurities on the GaN surface and result in a Ga/N stoichiometry of 1.02. Using atomic layer deposition with erbium tris(isopropylcyclopentadienyl) [Er((^{i}PrCp)₃] and water, crystalline cubic Er₂O₃ (C-Er₂O₃) is grown on GaN at 250 ⁰C. The orientation relationships between the C-Er₂O₃ film and the GaN substrate are C-Er₂O₃(222)

GaN(0001), C-Er₂O₃ (-440)

GaN (11-20), and C-Er₂O₃

GaN (1-100). Scanning transmission electron microscopy and electron energy loss spectroscopy are used to examine the microstructure of C-Er₂O₃ and its interface with GaN. With post-deposition annealing at 600 ⁰C, a thicker interfacial layer is observed, and two transition layers, crystalline GaN_wO_z and crystalline GaEr_xO_y, are found between GaN and C-Er₂O₃. The tensile strain in the C-Er₂O₃ film is studied with x-ray diffraction by changes in both out-of-plane and in-plane d-spacing. Fully relaxed C-Er₂O₃ films on GaN are obtained when the film thickness is around 13 nm. Additionally, a valence band offset of 0.7 eV and a conduction band offset of 1.2 eV are obtained using x-ray photoelectron spectroscopy.