XRD analysis ZnO grown by laser molecular beam epitaxy

Highly c-axis oriented ZnO epilayers were grown on α-Al₂O₃ (0001) substrates by laser molecular beam epitaxy (L-MBE) at a low substrate temperature. High resolution X-Ray diffractometer (Philips X`Pert HR-MRD) was used to investigate the structural proprieties of ZnO films. Glancing incidence X-Ray analysis (GIXA) technique was also conducted to analyze quantitatively the layer thickness, the surface roughness and the interface roughness of ZnO top layer and ZnO/Al₂O₃ interface. By the simulation of XRR curves, the calculated surface and interface rms roughness are 0.34 nm and 1.12 nm, respectively. XRD in-plane Φ scan results of ZnO and α-Al₂O₃ (0001) substrate show a 30° rotation of the ZnO unit cell with respect to the sapphire substrate, indicating the formation of the single aligned in-plane oriented domains. The results of XRD ω-2θ scan and ω rocking curve indicate that the strain of ZnO epilayer has been effectively relaxed, by the formation of aligned in-plane orientation and lattice relaxation, while the screw dislocations were also formed at the same time.