Preparation And Properties Of Indium Zinc Co-doped And Fluorine-doped Cuprous Oxide

Cuprous oxide?Cu₂O?is a direct band gap semiconductor which can be used to produce high efficiency solar cells.Cu₂ O has a forbidden band gap of about 2.1eV,and it has many other advantages,such as low fabrication cost,no toxicity and stability,etc.Cu₂ O can be potentially used in both photovoltaic and photocatalysis.Undoped Cu₂ O is a p-type conducting semiconductor.How to tailor its electrical and optical properties,including fabricating n-type Cu₂ O,tuning the optical band gap,achieving pn homojunctions and improving the photoelectric conversion efficiency,etc.has become the focus of studying Cu₂ O.In this paper,after investigating how to fabricate phase-pure Cu₂ O thin films,we studied doping Cu₂ O with both zinc?Zn?and indium?In?,or with fluorine?F?,and studied the electrical and optical properties of these samples.Firstly,how to obtain phase-pure Cu₂ O with direct current magnetron sputtering was studied.By changing the substrate temperatures,working pressure,sputtering power and the flow rate of O2 and Ar,a seriers of samples were made and the conditions were found.For example,when the substrate temperature was 400?,the working pressure was 2.0 Pa,the ratio of O2/Ar flow rate was 1 and 12,the sputtering voltage of the Cu target was 350 V,and the sputtering current was 40 mA,phase-pure Cu₂ O could be fabricated successfully.Secondly,Cu₂ O thin films co-doped with In and Zn were fabricated and their properties were studied.The samples were fabricated with co-sputtering a Cu target and an alloy target of Zn and In.It is found that when fixing the sputtering voltage and current of the Cu target,higher Ar flow rates such as 20 sccm will lead to the presence of Cu in the films,which suggests that the oxygen partial pressure is insufficient.Phase-pure Cu₂ O thin films can be obtained by properly increasing the voltage of the alloy target.However,the alloy target voltage can not be higher than that of the Cu target.Otherwise,it will result in other impurities,such as In2O3.The Cu₂ O thin films codoped with Zn and In have relatively higher transmittance above 500 nm,with an optical band gap of about 2.5eV which is bigger than that of undoped Cu₂O?2.1eV?.The samples fabricated with an alloy target voltage of 310 V are of n-type.XPS?X-ray photoelectron spectroscopy?measurement shows that samples containing copper,oxygen,indium and zinc.Copper atoms exist as Cu1+,indium atoms exist as In3+,and zinc atoms exist as Zn2+ in the samples.Very likely,both Zn and In are substitutional and act as donors in Cu₂ O,which finally makes Cu₂ O n-type.Thirdly,doping Cu₂ O thin films with F and their properties were studied.F-doping was realized with thermal diffusion.Phase-pure Cu₂ O thin films doped with F can be obtained at the diffusion temperatures of 850-1000?.EDS?Energy dispersive X-ray microanalysis system?measurement shows that all samples contain F element,indicating successful F-doping.Hall effect measurements show that all the samples are of p-type.F-doped samples have smaller band gaps than undoped samples,suggesting F-doping induces disorder in the films.When the diffusion temperature was 850?,the diffusion time was 30 min,the mass of CuF2 was 100 mg,the Ar flow rate was 100 sccm and the diffusion pressure was 400 Pa,F-doped Cu₂ O thin film with the smallest resistivity was fabricated,indicating potential applications in solar cells.