The present article evaluates, in qualitative and quantitative manners, the characteristics (i.e., thickness of layers, crystal structures, growth orientation, elemental diffusion depths, edge, and screw dislocation densities), within two GaN/AlN/Si heterostructures, that alter their efficiencies as positron moderators. The structure of the GaN film, AlN buffer layer, substrate, and their growth relationships were determined through high-resolution transmission electron microscopy (HR-TEM). Data resulting from high-resolution X-ray diffraction (HR-XRD) was mathematically modeled to extract dislocation densities and correlation lengths in the GaN film. Positron depth profiling was evaluated through an experimental Doppler broadening spectroscopy (DBS) study, in order to quantify the effective positron diffusion length. The differences in values for both edge $({\rho }_{\mathrm{d}}^{\mathrm{e}})$ and screw $\left({\rho }_{\mathrm{d}}^{\mathrm{s}}\right)$ dislocation densities, and correlation lengths (L^e, L^s) found in the 690 nm GaN film, were associated with the better effective positron diffusion length (L_eff) of $L_{\mathrm{eff}}^{\mathrm{GaN}2}$ = 43 ± 6 nm.

This study assesses the characteristics (edge and screw dislocation density) of a commercially available GaN/AlN/Al₂O₃ wafer. The heterostructure was evaluated by means of high-resolution X-ray diffraction (HR-XRD), high-resolution transmission electron microscopy (HR-TEM), and Doppler-Broadening Spectroscopy (DBS). The results were mathematically modeled to extract defect densities and defect correlation lengths in the GaN film. The structure of the GaN film, AlN buffer, Al₂O₃ substrate and their growth relationships were determined through HR-TEM. DBS studies were used to determine the effective positron diffusion length of the GaN film. Within the epitaxial layers, defined by a [GaN $P63mc$ (0 0 0 2) || $P63mc$ AlN (0 0 0 2) || (0 0 0 2) $R\overline{3}c$ Al₂O₃] relationship, regarding the GaN film, a strong correlation between defect densities, defect correlation lengths, and positron diffusion length was assessed. The defect densities ${\rho }_{\mathrm{d}}^{\mathrm{e}}=$ 6.13 × 10¹⁰ cm⁻², ${\rho }_{\mathrm{d}}^{\mathrm{s}}=$ 1.36 × 10¹⁰ cm⁻², along with the defect correlation lengths L^e = 155 nm and L^s = 229 nm found in the 289 nm layer of GaN, account for the effective positron diffusion length L_eff~60 nm.

In this study we analyzed the structure and light-sensing properties of as-deposited vanadium oxide thin films, prepared by RF sputtering in different Ar:O₂ flow rate conditions, at low temperature (e.g., 65 °C). X-ray diffraction (XRD), Scanning Electron Microscopy (SEM-EDX), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to analyze the film microstructure, composition and the oxidation states of vanadium ions. The SEM micrographs evidence V_xO_y films with smooth surfaces, whereas the XRD patterns show their amorphous structure. Raman spectra indicate an increased structural disorder in the films deposited in Ar:O₂ flow comparatively with those deposited solely in Ar flow. The XPS data suggest the modification of the oxidation state from V⁴⁺ to V⁵⁺, thus proving the formation of the V₂O₅ phase when increasing the oxygen content, which further affects the films’ optical properties. We observed a good stability of the photogenerated current in Si/SiO₂/V_xO_y/TiN heterostructures upon excitation with pulses of UV (360 nm), VIS (white light) and NIR (860 nm) light. The responsivity, detectivity and linear dynamic range parameters increase with the O/V ratio in the V_xO_y films, reaching comparable values with photodetectors based on crystalline V₂O₅ or VO₂.