Investigation On Nano ZnO And Doped ZnO Thin Films By MOCVD

In this paper,nano ZnO th in films were successfully prepared on quartz substrates by metal organic chemical vapor deposit ion.The influence of experimental condit ions on the preparation of ZnO films was studied.The effect of doping on its structure and optical properties was investigated by Na-N co-doping.The specific results were described as follows:The deposition temperature plays a crucial role in the growth of ZnO films.The substrate temperature of 800?is the best temperature for the growth of the crystal for our CVD equipment.The lower growth temperature is unfavorable for the growth of ZnO crystal due to the high nucleation barrier,while the higher growth temperature leads to the higher activation energy of atoms which is also not conductive to the formation of stable crystal.The gas flow rate of the oxygen source and the zinc source is an important parameter in the preparation of h igh quality th in films.The low flow rate of oxygen is not conducive to the oxidation of the zinc source and the crystal defect is thereby increased.And the high oxygen flow rate leads to a high total gas flow wh ich is not conducive to the growth of crystals.Furthermore,the excessive oxygen can also form oxygen-related defect to reduce the quality of the crystal.The gas flow rate of the zinc source also affects the crystal quality of the film.Therefore,the proper gas flow rate of oxygen source and zinc source is necessary for formation of high quality ZnO film.Based on the experiment,the optimal gas flow rate is 130sccm for oxygen and 150 sccm for zinc source for the growth of ZnO crystal.In the Na doping experiment,we find that when the gas flow of Na source is lower than 50 sccm,Na⁺ions main ly substitute for Zn²⁺ions.With the increase of gas flow of Na source,the grain size of the films increase,and the optical band gap widens due to the Moss-Burstein effect.When the gas flow of Na source is more than 50 sccm,the excess Na⁺ions will enter interstit ial gaps to form interstit ial defects,result ing in the decrease of grain size.The formation of defect level also leads to the optical band gap narrow down.In the N doping experiment,N atoms will firstly enter the interstit ial posit ion of ZnO crystal at the lower gas flow to produce the interstit ial defect and the crystal quality is thereby reduced.With the increase of the gas flow of N source,the interstitial N can produce the compensation effect with the oxygen vacancy,thus the quality of the film c rystal quality is improved.When the flow rate is further increased,the substitutional N atoms will be saturation and the excess N atoms will enter the interstitial that leads to the decrease of the crystalline quality of the film.Simultaneously,the optical band gap of the ZnO will be narrowed due to the electrons hybridization of the 2p orbit of N and the 2p orbit of O after the doping.