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 N-2 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((PrCp)-Pr-i)(3)] and water, crystalline cubic Er2O3 (C-Er2O3) is grown on GaN at 250 degrees C. The orientation relationships between the C-Er2O3 film and the GaN substrate are C-Er2O3(222) parallel to GaN(0001), C-Er2O3 < 440 > parallel to GaN < 11-20 >, and C-Er2O3 < 211 > parallel to 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 degrees C, a thicker interfacial layer is observed, and two transition layers, crystalline GaNwOz and crystalline GaErxOy, 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.