Pulsed Laser Deposition Of Zno Thin Films

ZnO is a wide band gap compound semiconductor(band gap:3.37eV at 300K), which has large exciton binding energy about 60meV.Theoretically,it can realize blueviolet and ultraviolet emission at room temperature.Such unique properties make it have many applications in Blue LED,Laser and related semiconductor devices. However,the bottleneck for ZnO applications is the fabrication of the producible,low resistivity,p-type ZnO films with high quality.So it is very important to investigate the fabrication and mechanism of p-type ZnO thin films.In this paper,we fabricated different ZnO thin films by pulsed laser disposition(PLD).By doping or implantating, we tried to fabricate p-type ZnO thin films.The results showed that phosphor doped ZnO thin films fabricated by P₂O₅ doped ZnO target and nitrogen doped ZnO thin films made by N implantation with PⅢcould be p-type ZnO thin films.In the experiments,we characterized the structures,components and properties using AFM, XRD,SIMS,XPS and Hall Measurements and systematically investigated the impacts of different experimental conditions on the structures and properties of ZnO films. The following are the results.1.The impacts of Si substrate and target impurity:ZnO thin film fabricated on p-type Si(100) substrate with different target purity(chemical purity99.5%and analytic purity 99.99%) exhibited low resistivity and extremely high Hall mobility. The samples with chemical purity(99.5%) are n-type while the samples with analytic purity are p-type.Results pointed out that the low resistivity and extremely high Hall mobility for two samples were mainly due to the contribution from Si substrate.In addition,the samples fabricated with chemical purity showed p-type conduction,which was probably caused by sulfur diffusing into Si substrate and formed S_si donor defects2.Phosphor doped ZnO thin film:experiment results indicate that p-type ZnO film can be obtained at optimal doping concentration,annealing temperature and annealing time.The electrical properties of the best sample are:resisitivity-2.63 Ohm·cm and carrier concentration-10¹⁷/cm³.XPS results show that P_o and P_Zn can exist at the same time.On the optimal experimental condition,when hole concentration produced by acceptors P_o is larger than electron concentration produced by donors P_Zn and native defects in ZnO,Phosphor doped ZnO films can become p-type.3.Nitrogen doped ZnO thin films:experiment results found that,p-type ZnO films can be obtained if they are implanted with proper N concentration and annealed at N₂.The electitircal properties of the best sample are:resisitivity-873 Ohm-cm and carrier concentration-1.3*10¹⁵/cm³.SIMS results prove that there are still N ions in the sample after annealing,which means N ions are the main reason for the conversion from n-type to p-type.In addition,nitrogen doped ZnO films will not become p-type if the concentration of N ions increase further,due to ion impair and N related donor defects.