Preparation And Photosensitive Properties Of Sn And Cr-doped Ln₂O₃ Films

In₂O₃is one kind of transparent conducting oxides with a good conductivity, hightransmittance of visible light, ultraviolet light strongly absorbing property. Due to its goodproperties, In₂O₃prepared Ultraviolet detector can apply to the environment which containslarge amount of infrared light and visible light but small amount of ultraviolet light. TheUltraviolet detection technology which can not be replaced by others plays an important rolein daily life, especially in the combustible gas plume detection, fire detection, photosensitiveskin detection and food disinfection and so on. At present, there is less study onphotosensitive properties of In₂O₃in internal and abroad, thus study on UV photosensitive ofIn₂O₃film is very meaningful work.In₂O₃film, Sn doped In₂O₃films and Sn, Cr doped In₂O₃films are deposited on glassand Si（004） substrate by magnetron sputtering technique. The crystal structures, the surfacemorphology of films, surface roughness, the valence state of doping elements, carrierconcentration, mobility, resistivity, the optical transmittance and UV photosensitive propertyare determined by x-ray diffraction （XRD）, Scanning electron microscopy （SEM） and Atomicforce microscopy （AFM）, X-ray Photoelectron Spectroscopy （XPS）, Hall measurementSystem, UV-Vis light spectrophotometer and Self-made UV photosensitive measurementrespectively. The research results indicated that:1) All the films consist of single phase of In₂O₃with cubic bixbyite structure, whichindicates the absence of an impurity phase in the films. With increase in the substratetemperature, the films with Sn doped are highly oriented along （222） direction, while thefilms with Sn and Cr doped change the preferred orientation from （400） to （222）. Sn dopedfilms and Sn and Cr doped films change the preferred orientation from （400） to （222） withoxygen flow rate increase. The 2θof this two diffraction peak have tiny displacement. It isbecause that Sn and Cr doped may lead to a disorder in In₂O₃film.2) The surface morphology and roughness of the films are relevant to grain size and thepreferred orientation of the films. The films grew in （400） preferred orientation, and havesawtooth-shaped surfaces, which is much rougher than the films with flat smooth surfacesgrew in （222） orientation. The grain size and roughness of the films increases with theincreasing temperature. While the grain size and roughness of the films decrease with theincreasing oxygen flow rate. 0.23at%Sn doped In₂O₃films and 0.23at%Sn and 1.29at%Crdoped In₂O₃films, which deposited at 600℃，0.4sccm oxygen flow rate, havesawtooth-shaped surface, and the latter films with the maximum of root mean square valuesof surface roughness（25nm）.3) According to the results of the hall measurement, with increase in substratetemperature, the carrier concentration increase, carrier mobility first increase then decrease, electrical resistivity decrease. 0.23at%Sn doped In₂O₃film deposited at 600℃，0.4sccmoxygen flow rate, has the maximum carrier concentration which is 1.29×10²¹cm^-3, and theminimum electrical resistivity is 2.88×10^-4cm. Meanwhile, as the same condition, thecarrier concentration of 0.23at%Sn and 1.29at%Cr doped In₂O₃film is 9.09×10²⁰cm^-3, andthe electrical resistivity is 3.27×10^-3 cm. The carrier concentration of 0.23at%Sn dopedIn₂O₃film is higher than one of 0.23at%Sn and 1.29at%Cr doped In₂O₃film. It is becausethat Cr²⁺ions and Cr³⁺ions enter into lattice, respectively instead of In³⁺ions and Sn4+ions.4) The transmittance of films has relationship with the carrier concentration and thesurface roughness of the films. All the films have strong absorption for ultraviolet light. Thehigher the carrier concentration is and the rougher the surface of the films is, the lower thetransmittance of the films is. The average percentage transmittance of Sn doped In₂O₃filmsand Sn, Cr doped films are about 75%, which meet the requirement of ultraviolet detector.According to the relationship among the transmittance, absorption coefficient and the opticalband gap, calculates the film band gap. The results found that the change of the optical bandgap is accordance with the change of the carrier concentration of the films. This phenomenoncan be explained by Burstein-Moss effect. The films with 0.23at% Sn doped In₂O₃films,deposited at 600℃, and an oxygen flow rate of 0.4 sccm, its optical band gap （3.69eV） isnarrower than intrinsic In₂O₃（3.75eV）.5) It is found from photosensitive testing that the sensitivity and response time of filmsto ultraviolet light have strong relationship with the quality of crystal and surface morphology.The worse the film density is and the higher the surface roughness is, the higher thesensitivity to ultraviolet light of the film has and the longer the response time is. At 600℃,0.4sccm oxygen flow rate, the value of sensitivity of Sn doped In₂O₃film is more than the Snand Cr doped In₂O₃film, and the response time is longer than the latter one.