Study On Photoelectric Properties Of Ion Co-implanted ZnO Films

ZnO is a wide direct bandgap semiconductor with a bandgap of～3.34 eV at room temperature and an exciton binding energy of～60 meV.The efficient UV emission of this material can be utilized in solid-state white light illumination devices.By doping with other elements,the band gap of ZnO can be tuned to narrow to the visible spectral region,enabling its application in light-emitting display devices such as solar cells and LEDs;by doping modulation with other elements,the structural properties and physical properties of ZnO can be suitably modified,enabling its use in optoelectronics,transparent thin-film transistors(TFTs),nanostructured materials,spintronics(spin+electronics)The research interest in a wide range of applications such as optoelectronics,transparent thin film transistors(TFTs),nanostructured materials,spintronics(spin+electronics),etc.is rising.Therefore,the doping of ZnO films with other elements can lead to the study of optimizing optoelectronic properties and imparting other physical properties with important theoretical and practical applications.The ion implantation technique is widely used in semiconductor doping and material surface modification,and its use in thin film doping separates the preparation and doping of thin films,which can solve the problems of unsatisfactory reproducibility and stability of ZnO thin films when the doping and preparation processes are carried out simultaneously.In this paper,we first select the molecular beam epitaxy technique to grow and prepare ZnO films on c-surface sapphire substrates,and grow the MgO buffer layer between ZnO films and sapphire substrates,which increases the lattice fitness between ZnO films and c-surface sapphire substrates and improves the crystal quality of ZnO films.Secondly,Co ions,Sm ions,Mn ions and As ions are separately or co-implanted into ZnO thin films.The effects of different types of ion implantation on the structure and optoelectronic properties of ZnO thin films are systematically investigated by the characterization methods,such as atomic force microscopy(AFM),X-ray diffraction(XRD),Raman spectroscopy,photoluminescence spectroscopy,absorption spectroscopy,transmission spectroscopy and spectroscopic ellipsometry(SE).Mechanism of half-metallic property of ZnO films implanted with Mn ions is analyzed by first-principles calculations.The main research contents and achievements are as follows:1.Co ions and Sm ions were separately and co-implanted into the O-polar ZnO films,which resulted in a larger surface roughness of the ZnO films,but the surface morphology of the co-implanted films was flatter than that of the single-injected samples.X-ray diffraction spectroscopy and Raman spectroscopy measurements indicated that the ZnO films had good quality and wurtzite structure.The UV luminescence peaks of Sm ion implanted ZnO films corroborated the luminescence properties of rare earth elements.In addition,the absorption and SE showed that the optical band gap of ZnO films became smaller after ion implantation,with the smallest band gap value for the ZnO films co-implanted with Co and Sm ions.After a deeper investigation,it was found that this was due to the generation of lattice defects and the increase of scattering loss below the band gap due to ion implantation.2.The electronic structure,density of states and energy band structure of electrons of wurtzite ZnO supercell(3 × 3 × 3)ZnO were calculated by density generalized theory for unimplanted and Mn ion-implanted ZnO films on first-principles calculations.The calculation results show that after Mn ion implantation,the valence band moved to the high-energy direction and the conduction band moved to the low-energy direction,making the band gap value after Mn ion implantation smaller than that of unimplanted ZnO.Near the Fermi energy level,there was a spin-up density of states on the Mn-3d orbitals but no spin-down density of states,so the Mn ion-implanted ZnO films had the half-metallic property.3.After different concentrations of non-metallic element As ions and the same concentration of transition metal element Mn ions were co-implanted into the ZnO films,the optoelectronic properties of the films changed with the increase of As ion concentration.On the surface morphology,the granularity of the surface became more obvious with the increase of the concentration.In terms of the lattice structure,no other impurity phases related to As or Mn ions were found by X-ray diffraction,indicating that co-implantation did not affect the wurtzite structure of the ZnO films or significantly change their crystalline quality.Secondly,the lattice constant of the film became larger and the grain size became smaller due to the presence of lattice defects,indicating that most of the As and Mn atoms were injected into the ZnO lattice,confirming the success of ion implantation.In the study of optical properties,transmission spectroscopy analysis showed that the absorption edge of the film was blue-shifted with increasing ion concentration due to the filling effect of the Burstein-Moss band in the implanted films.