Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future.

High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This “compliant” buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10⁵ cm⁻². In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6” wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

Superior energy storage density and efficiency along with excellent scalability are simultaneously achieved in the TiO₂/ZrO₂/TiO₂ antiferroelectric stack.

The thickness scaling of the ferroelectric (FE) hafnium zirconium oxide (HZO) down to sub-10 nm is essential in non-volatile memory devices. In this study, high remnant polarization (P_r), low thermal budget, low operation voltage, and high endurance are demonstrated in the FE HZO thin films with thickness shrinkage from 10 to 3 nm. Due to the in-plane tensile stress induced by the TiN capping layer and the initial island growth on the platinum bottom electrode, record-high P_r ∼24.8 μC cm⁻² is realized in the 6 nm HZO layer. Good ferroelectricity with P_r ∼10.8 μC cm⁻² and low saturation voltage (∼0.7 V) is also achieved in the 3 nm HZO thin film. The wake-up effect is insignificant as the HZO thickness is greater than 5 nm, while an obvious wake-up effect is observed in sub-5 nm HZO thin films. This result can be ascribed to the increasing stability of the tetragonal phase with a decrease of the HZO thickness as supported by the dielectric constant measurement. The dielectric breakdown strength of the HZO layers was evaluated by the time-zero dielectric breakdown test. The dielectric breakdown strength increases rapidly with a decrease of the HZO thickness, which leads to a significant endurance improvement with ∼10¹¹ electric field cycling without breakdown in the 3 nm HZO thin film. The favorable FE properties demonstrated in the sub-5 nm HZO thin films provide a promising approach in future FE non-volatile memory applications.

We report on the characteristics of near-band-edge (NBE) emission and deep-level band from ZnO/Al₂O₃ and ZnO/ZnO core-shell nanorod arrays (NRAs). Vertically aligned ZnO NRAs were synthesized by an aqueous chemical method, and the Al₂O₃ and ZnO shell layers were prepared by the highly conformal atomic layer deposition technique. Photoluminescence measurements revealed that the deep-level band was suppressed and the NBE emission was significantly enhanced after the deposition of Al₂O₃ and ZnO shells, which are attributed to the decrease in oxygen interstitials at the surface and the reduction in surface band bending of ZnO core, respectively. The shift of deep-level emissions from the ZnO/ZnO core-shell NRAs was observed for the first time. Owing to the presence of the ZnO shell layer, the yellow band associated with the oxygen interstitials inside the ZnO core would be prevailed over by the green luminescence, which originates from the recombination of the electrons in the conduction band with the holes trapped by the oxygen vacancies in the ZnO shell.PACS 68.65.Ac; 71.35.-y; 78.45.+h; 78.55.-m; 78.55.Et; 78.67.Hc; 81.16.Be; 85.60.Jb.