Interfacial structure of a-plane ZnO grown on r-plane sapphire by pulsed laser deposition

In this study, interfacial structure of a-ZnO with misfit accommodation on r  -sapphire at low and high growth temperatures (LT and HT) by pulsed laser deposition is presented. Along [11¯00]ZnO of large lattice mismatch of ZnO with sapphire, TEM examinations show that a-type misfit dislocations are spaced 1.3–2.2 nm on HT-ZnO/sapphire interface, whereas dislocation pairs in spacing of 2.8–3.5 nm are observed for LT-ZnO/sapphire. For smaller lattice mismatch along the ZnO c  -axis direction, reciprocal space maps of (112¯2¯)ZnO and (303¯0)sapphire reflections show that HT-ZnO is nearly fully strained without much relaxation and has a highly coherent interface with sapphire, in contrast with partial relaxation in LT-ZnO.

► Misfit accommodations for ZnO growth on r  –sapphire are observed to be varied with growth temperature. ► (112¯0)a-ZnO grown at 750 °C (HT-ZnO) shows that a-type misfit dislocations are spaced 1.3–2.2 nm in [11¯00]ZnO. ► Misfit dislocations pairs spaced with 2.8–3.5 nm in[11¯00]ZnO are observed in a–plane ZnO grown at 450 °C (LT-ZnO). ► HT-ZnO has a highly coherent interface with sapphire resulting in nearly fully strained lattice without much relaxation in ZnO c–axis direction. ► A few MDs with partial relaxation are observed in LT-ZnO/sapphire interface.