The high quality ZnO growth on c-Al ₂ O ₃ substrate with Cr ₂ O ₃ buffer layer using plasma-assisted molecular beam epitaxy

High quality epitaxial ZnO films were grown on c-Al ₂ O ₃ substrates with Cr ₂ O ₃ buffer layer by plasma-assisted molecular beam epitaxy (P-MBE). The hexagonal crystalline Cr ₂ O ₃ layer was formed by oxidation of the Cr-metal layer deposited on the c-Al ₂ O ₃ substrate using oxygen plasma. The epitaxial relationship was determined to be [ 1 over(1, ̄) 0 0 ]ZnO//[ 1 1 over(2, ̄) 0 ]Cr ₂ O ₃ //[ 1 over(1, ̄) 0 ]Cr//[ 1 1 over(2, ̄) 0 ]Al ₂ O ₃ and [ 1 1 over(2, ̄) 0 ]ZnO//[ 1 over(1, ̄) 0 0 ]Cr ₂ O ₃ //[0 0 1]Cr//[ 1 over(1, ̄) 0 0 ]Al ₂ O _3. The Cr ₂ O ₃ buffer layer was very effective in improving the surface morphology and crystal quality of the ZnO films. The photoluminescence spectrum showed the strong near band-edge emissions with the weak deep-level emission, which implies high optical quality of the ZnO films grown on the Cr ₂ O ₃ buffer.