Photoluminescence of ZnO and Mn-Doped ZnO Polycrystalline Films Prepared by Plasma Enhanced Chemical Vapour Deposition

ZnO and Mn-doped ZnO polycrystalline films are prepared by plasma enhanced chemical vapour deposition at low temperature （220℃）, and room-temperature photoluminescence of the films is systematically investigated. Analysis from x-ray diffraction reveals that a11 the prepared films exhibit the wurtzite structure of ZnO, and Mndoping does not induce the second phase in the films. X-ray photoelectron spectroscopy confirms the existence of Mn^2＋ ions in the films rather than metalic Mn or Mn^4＋ ions. The emission efficiency of the ZnO film is found to be dependent strongly on the post-treatment and to degrade with increasing temperature either in air or in nitrogen ambient. However, the enhancement of near band edge （NBE） emission is observed after hydrogenation in ammonia plasma, companied with more defect-related emission. Furthermore, the position of NBE shifts towards to high-energy legion with increasing Mn-doped concentration due to Mn incorporation into ZnO lattice.     

Investigation of Oxygen Vacancy and Interstitial Oxygen Defects in ZnO Films by Photoluminescence and X-Ray Photoelectron Spectroscopy

ZnO films prepared at different temperatures and annealed at 900^o C in oxygen are studied by photoluminescence （PL） and x-ray photoelectron spectroscopy （XPS）. It is observed that in the PL of the as-grown films the green luminescence （GL） and the yellow luminescence （YL） are related, and after annealing the GL is restrained and the YL is enhanced. The 0 ls XPS results also show the coexistence of oxygen vacancy （Vo） and interstitial oxygen （Oi） before annealing and the quenching of the Vo after annealing. By combining the two results it is deduced that the GL and YL are related to the Vo and Oi defects, respectively.     

Photoluminescence of ZnSe—ZnS Single Quantum Wells Grown by Vapour Phase Epitaxy

We study the photoluminescence (PL) of ultra thin layer ZnSe quantum Wells in ZnS barriers.Samples with different well widths are grown by vapour phase epitaxy and the PL spectra of these samples are measured by the excitation of a 500W Hg lamp.The peak positions of the bands coming from the excitonic luminescence show a larger blueschift with respect to the energy of free excitons in the ZnSe bulk material.The observed variation of the full width at half maximum and peak position of the bands in the spectra with the well width are interpreted to the formation of the ZnSxSe1-x alloy layer due to the interdiffusion in the interfaces between ZnSe and ZnS.According to the behaviour of the excitons in the smaller conduction band offset,the exciton binding energy is estimated from the dependence of the PL intensity on the temperature.from this result,excitons seem to show nearly three-dimensional characteristics.     

Near Band-Edge and Mid-Gap Photoluminescence of a ZnO Thin Film Grown on a （001） silicon Substrate

A nominally undoped wurtzite ZnO thin film of highly c-axis orientation was successfully grown on (001) silicon by metal-organic chemical vapour deposition, and its photoluminescence was measured as a function of excitation intensity at room temperature. The ZnO sample exhibited a strong near band-edge (NBE) line at 379.48nm (3.267eV) and a weak broad green band around-510 nm (2.43eV), showing a linear and sublinear excitation dependence of the luminescence intensity, respectively. No discernible intensity dependence of lineshape and emission peak was found for the NBE line. On the other hand, the peak energy of the green luminescence was found to increase nearly logarithmically with the increasing excitation intensity. The above results clearly indicate that in the ZnO epilayer, the NBE line was due to an excitonic spontaneous emission, while the mid-gap green luminescence can be assigned to the tunnel-assisted donor-acceptor pair (DAP) radiative recombination.Moreover, we obtained an energy depth β-11.74 meV for the potential wells due to the fluctuating distribution of the unintentional impurities/defects responsible for the tunnel-assisted DAP emission.     

optical, Structural and Laser-Induced Damage Threshold Properties of HfO2 Thin Films Prepared by Electron Beam Evaporation

We prepare HfO2 thin films by electron beam evaporation technology. The samples are annealed in air after deposition. With increasing annealing temperature, it is found that the absorption of the samples decreases firstly and then increases. Also, the laser-induced damage threshold (LIDT) increases firstly and then decreases.When annealing temperature is 473 K, the sample has the highest LID T of 2.17 J/cm^2, and the lowest absorption of 18ppm. By investigating the optical and structural characteristics and their relations to LIDT, it is shown that the principal factor dominating the LIDT is absorption.     

Structure and Photoluminescence of Nano-ZnO Films Grown on a Si （100） Substrate by Oxygen- and Argon-Plasma-Assisted Thermal Evaporation of Metallic Zn

Nano-ZnO thin films were prepared by oxygen- and argon-plasma-assisted thermal evaporation of metallic Zn at low temperature, followed by low-temperature annealing at 300℃ to 500℃ in oxygen ambient. X-ray diffraction patterns indicate that the nano-ZnO films have a polycrystalline hexagonal wurtzite structure. Raman scattering spectra demonstrate the existence of interface layers between Zn and ZnO. Upon annealing at 400℃ for i h, the interface mode disappears, and photoluminescence spectra show a very strong ultraviolet emission peak around 381 nm. The temperature-dependent PL spectra indicate that the UV band is due to free-exciton emission.