| Ⅱ-Ⅵ semiconductor films are widely used because of their excellent optical properties.CdSe films show high transmittance,high refractive index,high photosensitivity and high light absorbance in the near-infrared region,and have high stability and low manufacturing cost.Therefore,it has attracted extensive attention in the application of solar cells.In order to further optimize the optical and electrical properties of CdSe films,we have carried out different doping studies on CdSe films.Therefore,it has attracted extensive attention in the application of solar cells.In this thesis,the films are prepared by magnetron sputtering,and characterized by X-ray diffraction(XRD),ultraviolet visible near infrared(UV-Vis-NIR)spectrophotometer,field Emission scanning electron microscope(FESEM)and Hall effect measurement system.First,we prepared undoped CdSe films by RF(radio frequency)magnetron sputtering on glass and Si substrates.The effects of sputtering power and pressure on the structure,surface morphology and photoelectrical properties,electrical and optical properties of CdSe films are studied in detail.It is demonstrated by the XRD results that the CdSe films have a hexagonal crystal structure,which crystallize in CdSe(111)phase.The crystallinity of the CdSe films increases with the increase of sputtering power and decreases with the increase of sputtering pressure.FESEM study shows that the surface of the CdSe films is uniform and dense,and the grain size increases with the increase of sputtering power and decreases with the increase of sputtering pressure,which is consistent with the results of XRD.The resistivity of the CdSe films varies in the range of 0.124 ～0.561 Ω.cm.The optical band gap of the CdSe films varies in the range of 1.71 ～ 1.79 e V,which is close to the value of bulk material.Then,to improve the electrical and optical properties of CdSe films,Bi-doped CdSe(CdSe:Bi)films are prepared by the method of RF and DC(direct current)magnetron co-sputtering under separate conditions of different sputtering powers and different sputtering times.The effects of the Bi content on the properties of the CdSe:Bi films are studied in detail.According to the XRD pattern,diffraction peaks related to Bi element are not be found.It can be observed obviously that the intensity of the diffraction peak of the CdSe:Bi films is significantly higher than that of undoped CdSe films,indicating that appropriate doping of Bi can improve the crystallinity of CdSe films.The existence of Bi element is exposed by the EDX spectra of all samples,indicating that Bi has been successfully doped into CdSe films.With the increase of Bi content,the transmittance of the CdSe:Bi films decreases gradually and the optical band gap first decreases then increases.Compared with the undoped CdSe films(the minimum resistivity is 0.124 Ω.cm),the resistivity of the CdSe:Bi films decreases by 1-2 orders of magnitude(the minimum resistivity is 0.006Ω.cm).It is shown that Bi doping can significantly improve the electrical properties of CdSe films,but the optical properties are reduced.Finally,we try to further improve the optical and electrical properties of CdSe films by doping O element.Firstly,O-doped CdSe(CdSe:O)films are prepared by RF magnetron sputtering with single CdSe target by changing the flow ratio of argon and oxygen.XRD patterns show that the diffraction peak of CdSe(111)disappeared and the diffraction peak of CdSe(200)appeared,and the crystallinity of the CdSe:O films decreased significantly.In order to improve the crystallinity of CdSe:O films,CdSe:O films are prepared by RF magnetron co-sputtering with CdSe target and Cd O target by changing the sputtering power of Cd O target.The XRD patterns also show the existence of a single diffraction peak of CdSe(200).With the increase of doping power,the diffraction peak of CdSe(200)gradually increases,indicating that the crystallinity of the CdSe:O films is enhanced.The EDX spectra of all samples show the existence of O element,indicating that O has been successfully doped into CdSe films.The optical and electrical properties of the samples have been well improved.The maximum average transmittance in visible and near-infrared regions are 25.78%and 78.91% respectively,and the minimum resistivity is 0.0002 Ω.cm.In conclusion,the doped Cd O films has the potential to further improve the optical properties as a photovoltaic material. |
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