Preparation Of Zns Thin Films By Pulsed Laser Deposition And Properties Of The Study

Groupâ…¡-â…¥compound Zinc Sulfide(ZnS) is one kind of wide direct-band gap semiconductors materials with promising optical and electrical properties that make it widely used in a lot of fields,such as light-emitting diodes,α-particle detector,thin film batteries and electroluminescence.In this paper,ZnS films were deposited by pulsed laser deposition system. The deposition of the films and their optical and electrical properties were systemically studied under different substrates,deposition temperature,and annealing temperature.Besides,the crystal quality of the films was studied under different annealing mode.1.The ZnS films were prepared on glass substrates at different deposition temperatures such as 100℃,200℃,300℃,400℃,and 500℃.As the temperature rises,the intensity of the XRD diffraction peaks of(111) crystal direction enhance observably,and the FWHM first becomes wider,then narrower,in which,widest at 200℃,and narrowest at 500℃.From the results,we can see the crystal quality were better deposited under higher temperature.So high temperature can improve the transference of the films and the quality of crystal.2.The transmission spectrum of ZnS/Glass films were surveyed with the fluorescence photometer,from which we can know that,in the visible light scope,the transmission probability of varied from sixty percent to ninety percent,and the average level was better when the temperature was lower.The optical band gap E_g increased from 3.45eV to 3.67eV with the rising of the substrate temperature.The analysis band gap was at large smaller than 3.7eV,this is because the element S loses badly when deposited in such a high vacuum condition of 10^-5pa, which arouses the unbalance of the chemistry structure then the blueshift of the band gap. However,the rising of the temperature is propitious to improve the quality of the films,which make the band gap of the films close on that of the stuff materials.Using the optical band gap to distinguish theα-ZnS(002) from theβ-ZnS(111) in this experiment is a new method to estimate the structure of films in low temperature,which is far different from using the diffraction peak 2θ=28.5°to conclude the structure style of the films anciently.3.The ZnS films were deposited on p-Si(110) in different substrate temperature,from the XRD diffraction we can see that the films have many crystal line such as(111),(220) and(311), and the(111) orientation is the preferential growth orientation,whose intensity increases observably and FWHM becomes narrower with the rising of the substrate temperature.The AFM picture shows that the article becomes larger and the surface becomes rougher.All those results show that high temperature can strengthen the crystal degree although reduce the surface level at the same time.4.The ZnS films were deposited separately on glass and Si(100) substrates at 200℃,then annealed at different temperature such as 300℃,400℃å'Œ500℃,through the studying we can know that the crystalline size of films becomes first smaller then larger,which is consistent with what the AFM photograph shows.When annealed in 300℃å'Œ400℃,the transmission probability may decline below sixty percent,and the optical band gap move to blue.While annealed in a high temperature of 500℃can increase the transmission probability to eighty percent,keep the band gap the same to that without annealing,close to the band gap of the typical value of the bulk ZnS,about 3.6eV.The results show that annealing in a high temperature is better for the improvement of the crystal quality than in a low temperature.5.The ZnS films were deposited at 200℃substrate temperature.The influence of using different anneal method on the films was studied,one ways is annealing once for 1h at 500℃temperature,the other is annealing for many times at 500℃during the deposition.Through the comparison of the XRD diffraction peaks and the AFM pictures,we can discover that when annealing for many times,the(111) diffraction peaks is stronger,the surface is denser and the crystalline size is larger,which shows that different anneal method can affect the crystal quality of the films.We believe that annealing for many times during the course of deposition can relax the inner stress then improve the crystal quality of the films.