Study On Photoluminescence Of ZnO Thin Films Doped By Rare Earth And Silicon

With the development of optical communication technology,Er3+-doped semiconductors have attracted considerable interest these years,due to the relevant photoluminescence(PL)at around 1.54?m(4I13/2-4I15/2)which coincides with the absorption minimum in silica-based fibers.However,the special intra-4f shell structure of Er atoms imposes restrictions on the PL at 1.54?m,because it doesn't abide the energy transition selection rule proposed by Judd and Ofelt.That means the transition for 1540nm is forbidden,which is exactly the problem thousands of researchers spend so much effort on solving.After a lot of attempts,it's empirically known that a crystal field made by oxygen surrounding Er makes the intra-4f transition possible and even efficient;besides,choosing semiconductors with wide band gap could also enhance the PL.Taking the two factors above into account,the material zinc oxide(ZnO)incontrovertibly becomes a good choice.At room temperature(RT),ZnO has a direct band gap about 3.37eV and a large exciton binding energy of 60me V.It has attracted lots of attention of researchers due to its potential applications in optoelectronics(light emitting diodes,spintronic devices,transparent conductive electrodes,lasers,solar cells and so on)and others.In this paper,we investigated the grow conditions of ZnO:Er thin films by magnetron sputtering and studied the relation between the infrared PL and the conditions such as the thickness of film,the annealing temperature,the substrates and Si doping.Meanwhile we analyzed the suppression effect of diffused silicon from the substrate on Er-1540nm excitation in samples.During the whole experiment,Rutherford backscattering spectrometry was used to test the elements in films and estimate the thickness of samples.X ray diffraction spectrum was used to show the crystalline of films.The surface topography was obtained by the optical microscope and atomic force microscope.And all infrared spectra were gotten with a 532nm laser,InGaAs detector and other instruments.Based on Experiment results,we find that if the films are thicker,annealed at 250? and grown on Si-SiO2 substrate,the PL intensity will be larger.When samples are annealed at 550?,PL will decrease because of two reasons.On the one hand,the immediate states like defect states decrease.On the other hand,Si diffuses into films and the concentration of Si is so large that we can't ignore it.And the diffused Si will absorb the energy of pump used for the intrinsic luminescence and others,which reduces the luminescence efficiency of Er ions.We proposed a model to describe the process of energy transmission subsequently.Afterwards Si ions are implanted into samples.And we observe that when the concentration of Si is larger than that of Er ions,the transition for 1540nm will be forbidden again while it is allowed after the samples are annealed in nitrogen atmosphere.All results and conclusions above are meaningful to the Silica-based optoelectronics,and help perfect the theory of rare earth PL.