Photoluminescence Of ZnO Films Research Articles

Similar effects of the electric field and annealing on the near-band-edge photoluminescence in ZnO films

The response of the near-band-edge photoluminescence (PL) emission of ZnO thin films to annealing and the electric field’s action was investigated. These processes separately caused similar changes in the PL spectrum. The donor bound exciton emission at 3.36 eV, which is attributed to bulk defects, demonstrated invariance to any exposure, while the intensity of the 3.33-eV emission line decreased after annealing in nitrogen gas and was restored after annealing in an oxygen atmosphere. On the other hand, application of an electrical field during laser illumination resulted in the same change in the PL spectrum. The transition of defects related to the 3.33-eV emission from a radiative to a non-radiative state (and inversely) through the capture (release) of electrons was proposed as the mechanism responsible for the observed changes in the optical properties. The desorption of oxygen from the surface of the ZnO film during annealing in N2 or the motion of photogenerated electrons toward the surface during laser illumination were suggested to be the cause of this capture process.

Photoluminescence Spectra of thin Zno films grown by ALD technology

The photoluminescence of ZnO films grown by atomic layer deposition (ALD) on silicon substrates has been investigated. A new broad photoluminescence band has been revealed in the exciton region of the spectrum. The properties of the band in the spectra of the films with different crystallographic orientations of substrates have been studied in a wide temperature range at different excitation levels. A model describing the origin of the new band has been proposed.

Effect of Ag Thin Films on the Photoluminescence of ZnO Films.

The Ag-coated ZnO films were deposited on glass substrates using magnetron sputtering technique. Atomic Force Microscopy was employed to characterize the surface and the profile roughness of Ag-coated ZnO films. X-ray diffraction and X-ray photoelectron were used respectively to analyze the crystalline and chemical state of survey samples. The influence of capping Ag on the photoluminescence intensities of ZnO films has been investigated. The photoluminescence spectra were found to change as the deposited Ag varied with different deposition times and annealing temperatures. Relationships between the fabrication, characterization and performance of Ag-coated ZnO films are established. The results indicate that the diffusion of Ag into ZnO films and the upward bending of the energy band near the interface of ZnO/Ag led to the decrease of ultraviolet intensities of Ag-coated ZnO films. Due to the density of surface states on the bending of energy band, it is crucial to control the surface morphology of metal/ZnO for the enhancement of light emission.

Effect of Rare-Earth Doping on Structural and Luminescent Properties of Screen-Printed ZnO Films

The effect of Sm3+ and/or Ho3+ doping on structural and luminescent properties of screen-printed ZnO films sintered at 1000°C was investigated by photoluminescence (PL), PL excitation and Raman scattering methods. For all the films, ultraviolet excitonic and visible defect-related PL bands of ZnO were detected. The doping with Ho3+ ions produced an enhancement of PL in ZnO films, the excitonic PL intensity being increased prominently, while the co-doping with Sm3+ and Ho3+ ions resulted in PL decrease in ZnO films. Only for (Sm,Ho)- co-doped ZnO films, the rare-earth PL bands were detected. The reduction of Sm3+ to Sm2+ was observed demonstrating 5D0→7FJ radiative transitions. The mechanism of PL and PL excitation is discussed in terms of the formation of rare-earth complexes as well as energy transfer towards them from ZnO host.

金纳米颗粒等离激元对不同形貌氧化锌薄膜发光性能的调控

金纳米颗粒等离激元对不同形貌氧化锌薄膜发光性能的调控

Sb doping behavior and its effect on crystal structure, conductivity and photoluminescence of ZnO film in depositing and annealing processes

The Sb-doped ZnO (ZnO:Sb) and undoped ZnO films with wurtzite structure and (0 0 2) preferred orientation were deposited on Si(1 0 0) substrate at 550 °C. It is deduced from XRD and XPS measurements that the Sb in the as-grown ZnO:Sb has high oxidation state and dopes in the form of oxygen-rich Sb–O clusters, which results in a large inner stress and a great increase of the c-axis lattice constant. After annealing at 750 °C under vacuum, the c-axis lattice constant of the ZnO:Sb decreases sharply to near the value of ZnO bulk, the electrical properties change from n-type to p-type and the PL intensity ratio of the visible to ultraviolet emission band goes down greatly, as the Sb content increases from 0 to 2.1 at.%. EDS and XRD measurements indicate that some of Sb dopants escape from the ZnO:Sb films and the oxygen-rich Sb-O clusters vanished after the annealing process. The effect of the change in Sb doping behavior on crystal structure, conductivity and PL is discussed in detail.

Investigation of room temperature UV emission of ZnO films with different defect densities induced by laser irradiation

We studied the room temperature UV emission of ZnO films with different defect densities which is fabricated by KrF laser irradiation process. It is shown room temperature UV photoluminescence of ZnO film is composed of contribution from free-exciton (FX) recombination and its longitudinal-optical phonon replica (FX-LO) (1LO, 2LO). With increase of the defect density, the FX emission decreased and FX-LO emission increased dramatically; and the relative strengths of FX to FX-LO emission intensities determine the peak position and intensity of UV emission. What is more, laser irradiation with moderate energy density could induce the crystalline ZnO film with very flat and smooth surface. This investigation indicates that KrF laser irradiation could effectively modulate the exciton emission and surface morphology, which is important for the application of high performance of UV emitting optoelectronic devices.

Effects of localized surface plasmons on the photoluminescence properties of Au-coated ZnO films

The ultraviolet (UV) emission from the Au-coated ZnO films was greatly enhanced and the visible emission was significantly suppressed compared with the un-coated ZnO films. Great changes in photoluminescence of ZnO films are attributed to the electron transfer between conduction band and defect levels through the localized surface plasmons. The increase of electron density in conduction band causes enhanced UV emission, while the decrease in electron density in defect level leads to the suppression of the visible emission. Such ZnO films with enhanced UV emission have potential applications in the highly efficient solid state emitters.

Effects of annealing and supersonic treatment on the structure and photoluminescence of ZnO films

We have deposited ZnO thin films on the Si (1 0 0) substrate at 473 K using facing-target magnetron RF sputtering system and have investigated the effect of annealing and supersonic treatment on the structure and photoluminescence (PL) of ZnO thin films. The results showed that as-deposited ZnO thin film displayed a bad preferential C-axis (0 0 2) orientation. As the annealing temperature increased from 673 to 973 K, the preferential C-axis orientation changed to better gradually. Meanwhile, scanning electronic microscopy (SEM) observation showed that the as-deposited ZnO thin film grew in columnar form and the grain size was approximately from 20 to 50 nm. In addition, the PL spectrum showed that the as-deposited ZnO thin film had no emission peak. When the annealing temperature reached 673 K, a weak violet peak with 398 nm was observed. As the annealing temperature increased to 773 K, the intensity of the violet peak increased and an ultraviolet peak with 378 nm was observed. Besides, ZnO thin films annealed at various temperatures had no green emission peak, while for ZnO thin films annealed at 973 K and then treated by supersonic, a strong and wide green emission band was observed.

Electrophotoluminescence of ZnO film

The electric-field-controlled photoluminescence (PL), i.e., electrophotoluminescence (EPL) of ZnO film has been investigated via a ZnO-based metal-insulator-semiconductor (MIS) structure on a silicon substrate applied with different biases. Compared with the PL of ZnO film in the case where there is no bias on the MIS structure, the positive bias with negative voltage applied on silicon substrate significantly enhances the near-band-edge ultraviolet emission while suppressing the deep-level-related visible emissions, whereas the negative bias hardly changes the PL of ZnO film. The mechanism for EPL of ZnO film is proposed in terms of the electric-field effect on the bending of energy bands of ZnO.

Influence of annealing temperature on the microstructure and photoluminescence of ZnO films

ZnO thin films with strong c-axis prefered orientation have been successfully deposited on Si(100) substrate at 750℃ by using reactive radio frequency magnetron sputtering. The influence of annealing temperature ranging from 600 to 1000℃on the microstructure and photoluminescence (PL) properties of ZnO films was investigated by Ｘ-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence measurement at room temperature. The XRD and TEM results show that the grain size of ZnO film increases and the residual stress in the film is tensile and remains constant at about 1 GPa with the increase of annealing temperature below 900℃. After annealed at 1000℃, the grain size decreases and the residual stress in the film changes into compressive with the value about -2 GPa. The PL spectra of the ZnO films show two emission bands, namely that originating from ultraviolet (UV) exciton transition and the visible defect photoluminescence. The intensity of UV PL spectrum and the relative intensity of fferent exciton emission are dependent on the grain size and defects in the ZnO film. The red shift of UV PL spectrum results from the change of the relative intensity of different exciton emission with annealing temperature. The visible PL spectrum is sensitive to the change of annealing temperature. The relationship between PL spectra and microstructure and defects in the films is discussed.

Rapid preparation, characterization, and photoluminescence of ZnO films by a novel chemical method

A novel and simple chemical route was developed for the deposition of ZnO film from aqueous solution, integrating the merits of successive ionic layer adsorption and reaction and chemical bath deposition. ZnO thin films on glass and Si(1 0 0) substrates were deposited with the precursor of zinc–ammonia complex. As-deposited ZnO film exhibits good crystallinity with the hexagonal wurtzite crystalline structure and the preferential orientation along (0 0 2) plane. With a dense and continuous appearance, the film is composed of ZnO particles in even size of 200–300 nm. Under the excitation of 340 nm, strong and sharp near band gap emission (∼391 nm) dominates the photoluminescence spectra with several weak emission peaks related to the deep level (∼450–500 nm). In addition, the mechanism for the deposition process of ZnO from aqueous solution was preliminarily discussed.

Effects of annealing on the structure and photoluminescence of ZnO films

Highly oriented polycrystalline ZnO films have been prepared by rf actively sputtering technique. We have investigated the structural and optical properties of ZnO films. x-ray diffraction was employed to analyze the influence of the post-treatment on the properties of ZnO thin films. The grain size increases with annealing temperature. The shift of the diffraction peak position from its normal powder value was observed. The photoluminescence (PL) spectra of these samples consist of one emission peak centred at 2.9eV.The intensities of PL peaks decrease with increasing annealing temperature. We propose that the emission comes from the interstitial Zn.