Preparation And Properties Of Nitrogen Doped ZnOS Thin Films Grown By PLD

To realize the application of ZnO in optoelectronic devices,a stable,reliable,high quality p-type ZnO material is indispensable.Wurtzite ZnO naturally as n-type semiconductors has been proven to be difficult to doped p-ype.At present,the reseach of p-type ZnO mainly focus on doping with group V element,where N and O atoms have similar ionic radius and electronegativity.So N element is the best choice to realize p-type doped ZnO.However,based on theoretical calculation,nitrogen is actually a deep acceptor level in ZnO,with an exceedingly high ionization energy of 1.3 eV.Therefore,the N doped cannot lead to hole conductivity in ZnO.Recently,Persson et al.theoretically revealed that the ZnOS alloys exhibit a very strong valence band(VB)-offset bowing as a function of S content,resulting in that the valence band maximum(VBM)lift strongly whereas the conduction band minimum(CBM)keeps the position for small S incorporation.The strong VB-offset bowing can be utilized to reduce the acceptor level,which is helpful to form No substitute with lower formation energy and shallower acceptor state and it is easier to get p-type doped ZnO alloy.Therefore,the purpose of this paper is to explore a suitable N doping process conditions of the ZnOS alloy films,and study their structure and performance systematically.By using a ZnS ceramic target and different N source as the reactive gas,we have deposited ZnOS thin films by pulsed laser deposition(PLD)on c-plane sapphire substrates.Different technological conditions of the ZnOS thin films have been systematically studied,and the main contents and results are as follows:1.The substrate temperature was fixed at 750 ?,effects of different N2 and O2 partial pressure on the surface morphology,crystal structure,composition,optical properties and nitrogen doping of the films were systematically studied.The results show that the surface of ZnOS thin films is smooth and the root mean square roughness(RMS)is less than 4.3 nm.The obtained films were crystalline in single-phase hexagonal structure along with c-axis preferred orientation at the 10 Pa N2 and 5 Pa N2,2 Pa O2 partial pressures respectively,and the optical transmittance of the films in the wavelength range of the visible light are above 80%.Particularly,when the N2 partial pressure is 10 Pa,the XPS test shows that there is an obvious N Is peak at 405.2 eV comes from N-N bond.2.The NO partial pressure was fixed at 3 Pa,Effects of different substrate temperatures on the surface morphology,crystal structure,composition and optical properties of the films were compared,the best substrate temperature of film growth is determined.The results show that c-plane orientated ZnOS films of single-phase was obtained at a substrate temperature of 600 ?,and the optical transmittance of the films in the wavelength range of the visible light is about 85%.3.The substrate temperature was fixed at 750 ??the surface morphology,crystal structure,composition and optical properties of the films were studied at different NO partial pressures.We have obtained the epitaxial growth of wurtzite structure ZnOS films with a series of sulfur content by adjusting NO partial pressures.Single-phase ZnO1-xSx alloys with wurtzite structure were achieved in composition ranges of 0.197?x?<0.261 and 0.623 ?x?0.962,and phase separation of O-rich wurtzite ZnOS and S-rich wurtzite ZnO1_xSx exists in ZnO1-xSx ternary alloys of compositions of 0.261<x<0.623.The band gap energy can be tuned from 2.92 eV to 3.61 eV,showing a nonlinear variation with a bowing behavior.At the same time,the N Is peak is observed by Narrow-scan spectra of XPS at NO pressures of 2 Pa,2.5 Pa and 3 Pa,corresponding to 0.43 at.%,0.81 at.%and 0.91 at.%of N concentration..The N 1s core level at-396.52 eV for ZnO1-xSx films,which is assigned to N-Zn bond or No acceptor.It proved we have successfully prepared the N doped ZnOS films.4.The single phase ZnOS films were researched by using N ion implantation and different pulse laser annealing.The surface morphology,crystal structure,composition and optical properties of thin films were studied.The structure and composition of ZnOS films had no obvious changes in different conditions.The band gap chang from 2.93 eV to 3.02 eV,the optical transmittance of the films in the wavelength range of the visible light is about 90%.