Properties And Research Of Rare Earth Doped In₂O₃ TFT Prepared By Solution Method

Indium oxide（In₂O₃）,as one of the most important transparent oxide semiconductor materials,has attracted much attention due to its high carrier mobility and wide optical band gap.However,In₂O₃ TFTs are often difficult to control off-state current and threshold voltage in pure In₂O₃ TFTs due to higher carrier density.Moreover,the stability of the device under various stress conditions such as voltage,heat,light and environment is not suitable for practical use in the substrate of flat panel displays（FPDs）.By doping foreign ions,the conductivity and carrier concentration of the transparent oxide semiconductor film can be lowered.It also increases the switching ratio(I_ON/I_OFF),threshold voltage(V_TH)and subthreshold swing（S）of the TFT device.The choice of suitable dopants generally depends on the low standard electrode potential of the doped foreign ions,low electronegativity,and high bond energy of the foreign ions combined with the oxygen ions.Because of its lower SEP,lower electronegativity and higher binding energy to oxygen can effectively increase the metal-oxygen lattice,reduce oxygen vacancies and hydroxide-related groups,and improve the performance of In₂O₃ based devices.China is a large country with rare earth elements.The use of rare earth elements doping can form a formula of China’s independent intellectual property rights.It can interrupt the monopoly of indium gallium zinc oxide thin film transistors（IGZO-TFT）in Japan and other countries.At the same time,the doping of rare earths is also consistent with the standard for dopant selection.Therefore,doping rare earth elements is a dopant material that is considered to be the most promising to improve the performance of In₂O₃ TFTs.In addition,we have chosen a process-solution method for film preparation that is environmentally friendly,low cost,and simple,and is advantageous for large-scale production of devices.In this paper,three kinds of rare earth elements（X=Pr,Dy,Yb）were selected and the In-X-O film and TFTs were prepared by the aqueous solution method.The effects of different concentrations of rare earth elements on the properties of In₂O₃ thin films and devices were systematically investigated by means of characterization.The main contents are as follows:First,the effects of different amounts of Pr on In₂O₃ thin films and devices were investigated.The amount of Pr doped first did not have much to do with the surface roughness of the film,and all films exhibited very smooth and uniform.Secondly,the crystal structure of the film did not change with the addition of Pr.It is shown that the doping of different contents does not substantially change the surface morphology and crystal structure of the film.Finally,the transfer curve of the device doped with different content of Pr,whether it is from forward scan or reverse scan,causes a very small ?V_TH shift,and the 5%Pr-doped In Pr O TFT exhibits the best performance:μ=7.68 cm²/V^-1s^-1,I_ON/I_OFF=1.10×10⁶,S=1.62 V/dec,V_TH=4.23 V.Second:The effects of different Dy doping concentrations on In₂O₃ films and devices were investigated.According to the literature research and exploration,the doping ratio of Dy was selected to be 0%,2%,5%,10%,20%,and the concentration of the precursor solution was 0.2 mol/L.These five concentration ratios of In Dy O TFTs were then prepared.Firstly,the surface roughness of the film is not affected by Dy doping,and the film is very smooth,which is beneficial to the transportation of the carrier.Secondly,the increase of Dy doping will increase the optical band gap of the In Dy O film and the crystallinity of the film,but the excessive doping（>20%）will change the In Dy O film into an amorphous phase.Finally,as the doping ratio of Dy increases,the positive and negative bias stability of the In Dy O film also increases.And its performance is best represented by 10%Dy doping:μ=7.60 cm²/V^-1s^-1,I_ON/I_OFF=1.15×10⁸,S=0.77 V/dec,V_TH=1.78 V.Third:Through the characterization of the surface structure,optical and electrical properties of InYbO films,the effects of different concentrations of Yb on In₂O₃ films and devices were investigated.Surface structure:By characterization of TEM,XRD and XPS of InYbO films doped with different concentrations of Yb,it was found that the prepared active layer InYbO film was in close contact with the insulating layer Si O₂,and there was almost no void,indicating that the quality of the film preparation was high.Further,as the doping concentration of Yb,the crystal structure of the InYbO film hardly changes,and both are polycrystalline phases.And the crystallinity of the film is increased.Optically:InYbO films doped with different concentrations of Yb exhibit optical transmittance,which means they are completely transparent display channel materials.And by analyzing the PL of different concentrations of InYbO film,it is shown that the increase of Yb doping concentration,the intensity of orange luminescence of InYbO film at 600 nm is weakened,which is related to the decrease of oxygen vacancies in InYbO film.Electrically,the bias stability of InYbO TFT is positively correlated with the doping concentration of Yb.The device exhibits the best performance at a doping concentration of 10%:μ=8.00 cm²/V^-1s^-1,I_ON/I_OFF=6.19×10⁷,S=0.95 V/dec,V_TH=5.61 V.