Post-annealing treatment is a necessary process to create/eliminate/repair defects in self–assembly (SA) metal oxide by providing enough thermal energy to the O atoms to overcome the migration energy barrier in ZnO. The height of migration energy barrier is dependent on the depth from the surface, which is hard to be estimated by theoretical calculations, as well as the optical analyses. SA ZnO nanorods (ZNRs) have high surface-to-volume ratio to provide complete picture between the optical and surface properties obtained by photoluminescence (PL) and ultraviolet/X-ray photoemission spectroscopy (UPS/XPS), which is used to investigate the evolution of structure and chemical states of the surface layers to reveal mutual agreement on all observations in PL, XPS, and UPS. We demonstrate variation of the surface structure of SA-ZNRs by scanning over a range of annealing temperatures and time to regulate the structure variation of SA-ZNRs, and their optical analyses agrees well with PL, XPS and UPS, which indicates the dependence of migration energy barriers on the depth from the surface of ZNR. The results reveal the well ZNRs formed at 570 °C and the further oxidation process and the formation of hydroperoxide on the Zn-rich surface of ZNRs at 640 °C.

In fabricating advanced silicon (Si)-based metal–oxide semiconductors, the ability to inspect dopant distribution in Si ultrathin films (tens of nm) is crucial for monitoring the amount of dopant diffusion. Here, we perform an anisotropic reflective second harmonic generation (SHG) measurement to demonstrate the sensitivity of SHG to phosphorus (P) concentration within the range of 2.5×1017 to 1.6×1020 atoms/cm3. In addition, we propose an analysis method based on a simplified bond-hyperpolarizability model to interpret the results. The bond vector model that corresponds to the P vacancy clusters is built to calculate the SHG contribution from substitutionally incorporated P atoms. The effect of incorporating P into the Si lattice is reflected in the effective hyperpolarizability, lattice tilt, and deformation of this model. The fitting results of the intuitively defined coefficients exhibit a high correlation to the P concentration, indicating the potential of this model to resolve the properties in complex material compositions. Finally, a comparison with Fourier analysis is made to evaluate the advantages and disadvantages of this model. Combined anisotropic reflective SHG (Ani-RSHG) and the simplified bond-hyperpolarizability model (SBHM) can analyze the crystal structure of doped ultrathin films and provide a non-destructive nanophotonic way for in-line inspection.

No abstract

In conventional ZnO/Si heterostructures, a buffer layer is usually required to compensate the mismatch between the host substrate and the grown thin film. However, poor quality of buffer layers might lead to severe crystalline misorientation and defects. In this work, we demonstrate that collective oxidized Zn dots act as buffer and seed layers for the growth of high surface quality ZnO thin films on Si(111) by rf-sputtering, and we further in situ analyze the structural evolution by reflective second harmonic generation (RSHG). The collective Zn dots grown on Si(111) were oxidized with exposure to ozone gas under proper Ultraviolet-C (UVC) irradiation, and then these ZnO shells formed seed layers to promote the nucleation process for subsequent ZnO thin film growth. Besides, RSHG was performed in situ to observe the net symmetrical dipole contribution at each fabrication steps and analyzed the surface quality of the ZnO thin film. Consistent with the analyses of synchrotron x-ray diffraction and atomic force microscopy, the RSHG results analyzed with simplified bond-hyperpolarizability model fitting revealed that well oxidized Zn dot-embedded ZnO films grown on Si(111) exhibit a 3m-symmetrical surface structure, and that excessive oxidation time led to ZnO2 formation and higher roughness. Our results demonstrate the efficient approach toward high-surface-quality ZnO thin film by rf-sputtering, verifying that the quality of ZnO shell covering Zn dot grown on Si(111) is the focal factor for the sequent ZnO thin film growth.

Si/SiGe stacked multilayers are key elements in fabrication of gate-all-around (GAA) structures and improvement of electrical properties, with the evolution of the Si/SiGe interfaces playing a crucial role. In this work, a model is developed based on the simplified bond hyperpolarizability model (SBHM) to analysis the anisotropic reflective second harmonic generation (Ani-RSHG) on a three-period stacked Si/Si1−xGex multilayer, which builds on Si(100) diamond structures. The C4v symmetry of the Si(100) structure enables the second harmonic generation (SHG) contribution from the bonds to be simplified and the effective hyperpolarizabilities of the interfacial and bulk sources to be obtained. The effective interface dipolar and bulk quadrupolar SHG hyperpolarizabilities in the Si1−xGex sample with various Ge concentration profiles are modeled by interpreting the concentration of a component element as the probability of the element occupying an atomic site. On the basis of the developed model, the Ani-RSHG spectra of the as-grown samples with various Ge ratios for each layer and the samples annealed at 850 °C and 950 °C are analyzed to inspect the change in Ge distribution and its gradient in depth. The Ani-RSHG analysis on as-grown samples showed difference in Ge distribution in samples with the multi Si/SiGe structure, which is not well observed in synchrotron X-ray diffraction (XRD) spectra. For the annealed samples, the response to changes in Ge concentration and its gradient in depth reveal the Si/Si1−xGex interface intermixing. Results of high-angle annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy agree well with the Ani-RSHG with SBHM findings. Compared with the Raman and synchrotron XRD spectra, the Ani-RSHG with SBHM simulation result demonstrates much better response to changes in compositions of the Si/Si1−xGex stacked multilayered structures, verifying the potential for characterizing the concentration distribution in stacked multilayered thin films for GAA structures.