Atomic layer deposition of CdO and CdxZn1−xO films

• Polycrystalline CdxZn1−xO deposited via ALD at 150 °C for the first time.
• CdO {111} planes are strongly oriented parallel to SiO2/Si(100) substrates.
• Crystallinity shifts from cubic (CdO) to hexagonal (ZnO) without an observed amorphous region.
• Bandgap bowing occurs due to the valence band offset and lattice mismatch of the binary materials.

Growth of CdxZn1−xO by atomic layer deposition (ALD) is demonstrated at 150 °C using diethylzinc (DEZn), dimethylcadmium (DMCd), and water as the precursors. The relative ratio of the DMCd and DEZn pulses is varied to achieve different compositions ranging from pure CdO to pure ZnO. The crystal structure of CdO is rock salt cubic and that of ZnO is hexagonal, and the alloy from ZnO to at least Cd0.56Zn0.44O has a hexagonal crystal structure. Transmission electron microscopy confirms polycrystalline grain features and a growth rate of ∼2.0 Å cycle−1, while selected area diffraction provides crystallographic information indicating that {111} type planes of the pure CdO ALD film are preferentially oriented to the film surface. Using spectroscopic ellipsometry, the film's optical constants are correlated with elemental composition and crystal structure. Control of these properties allows for tuning of the optical bandgap and index of refraction.