Microstructural and morphological properties of homoepitaxial (001)ZnTe layers investigated by x-ray diffuse scattering

Abstract

The microstructural and morphological properties of homoepitaxial (001)ZnTe layers grown by metalorganic vapor phase epitaxy at a temperature (TG) between 325°C and 400°C are investigated by x-ray diffuse scattering. High resolution reciprocal space maps (RSMs) recorded close to the ZnTe (004) Bragg peak show different diffuse scattering features that can be ascribed to (i) the specific surface morphology of the sample, and (ii) the presence of extended lattice defects in the epilayers. One kind of cross-shaped diffuse scattering streaks, appearing for TG⩾350°C, extend along ⟨111⟩ directions and can be attributed to stacking faults (SFs) occurring at the epilayer–substrate interface, within the epilayers. The SF diameter was estimated around 200–300nm, while their density increases with TG. Another kind of cross-shaped diffuse streaks, inclined at an angle β≈80° with respect to the ⟨110⟩ in-plane direction, arises from the morphology of epilayers grown above 360°C, their surfaces being covered by pairs of pyramidal hillocks up to a density of 106–107cm−2. Atomic force microscopy (AFM) measurements showed that the apex angles of the pyramids compare well with the value of 2β. The hillock formation is ascribed to Te adatoms experiencing a Schwoebel potential barrier at the step edges around pairs of partial dislocations (dipoles) bounding the SFs. In a quite narrow growth temperature interval around 350°C no β-crossed diffuse streaks are instead observed in the RSMs, indicating a smooth ZnTe surface. Finally, at a lower growth temperature (TG=325°C) a diffuse scattering intensity distribution defined by an angle γ≈63° with respect to the ⟨110⟩ in-plane direction is observed, corresponding to a dense ridging of the epilayer surface along the perpendicular direction. Both RSM analysis and AFM measurements indicate that the ridge sidewalls are {113} planes.