Insight into the effect of screw dislocations and oxygen vacancy defects on the optical nonlinear refraction response in chemically grown ZnO/Al2O3 films

Abstract

We report the effect of screw dislocations and oxygen vacancy defects on the optical nonlinear refraction response of ZnO films grown on a sapphire substrate at various oxygen flow rates using the chemical vapor deposition technique. The nonlinear refraction response was investigated in the off-resonant regime using a CW He-Ne laser source to examine the role of the intermediate bandgap states. It has been observed that the structural defects strongly influence the optical nonlinearity in the off-resonant regime. Nonlinearity has been found to improve as the oxygen flow rate is lowered from 2 sccm to 0.3 sccm. From photoluminescence studies, we observe that the enhanced defect density of the electronic defect levels due to the increased concentration of structural defects (with the decrease in the oxygen flow rate) is responsible for this improved optical nonlinearity along with the thermal effect. This suggests that defect engineering is an effective way to tailor the nonlinearity of ZnO films and their utility for optoelectronic device applications.

Rich Surface Oxygen Vacancies of MnO2 for Enhancing Electrocatalytic Oxygen Reduction and Oxygen Evolution Reactions

“…[ 34,35 ] Similarly, the pure β‐MnO 2 (JCPDS PDF 24‐0735) samples were obtained via the heating treatment procedures under different atmospheres (Figure 2b). [ 36 ]…”

Vacancy-enhanced generation of singlet oxygen for photodynamic therapy

“…S4†). For BiOBr–H, an intermediate energy level appears in the forbidden zone, resulting from the presence of abundant oxygen vacancies 34,35. The density of states of BiOBr–H indicates that the intermediate energy level is mainly composed of Bi-6p orbitals (Fig.…”

Oxygen vacancy engineering of MOF-derived ZnO/Co3O4 nanocomposites for high harmonic mode-locking operation

“…Actually, the fast change rate of the modulation depth of ZnO/Co 3 O 4 -N is due to the fact that a higher oxygen vacancy concentration changes the electronic states of the carriers and improves the photogenerated electron-hole separation, thus enhancing the effect of light-matter interactions and the nonlinear optical absorption response. 37,48,57 Therefore, by controlling the oxygen vacancy concentration, the nonlinear absorption response of the material is improved and the saturable absorber with a higher modulation depth and a lower saturation light intensity is more likely to generate modelocked pulses with a high repetition frequency.…”

“…[32][33][34] Actually, abundant oxygen defects can create new energy levels in the forbidden gap, resulting in a reduced bandgap and a red shift in the absorption spectrum, 35 as well as improved optical nonlinearity. 36,37 Although ZnO/Co 3 O 4 nanocomposites can be uniformly synthesized with a better performance, 38,39 their optical nonlinear features are still missing and the impact of the oxygen vacancies on the saturable absorption is not fully understood yet.…”