Investigation On The Effect Of Annealing On Optical,Electrical Properties And Intrinsic Defects Of ZnO:In-N Thin Films

ZnO is a direct bandgap semiconductor material with a wide bandgap of 3.37 e V at room temperature.Compared to the Ga N,ZnO has a larger free exciton binding energy（60 me V）that ensures efficient exciton emission at room temperature,which makes it a promising candidate in the field of optoelectronics,such as ultraviolet light-emitting diodes（LEDs）,laser diodes（LDs）,photoelectrochemical immunosensor,and solar cells.However,many intrinsic defects(Zn_i,V_O,O_i,V_Zn)have been found in ZnO thin films after ion implantation.These defects have a great influence on the structure and photoelectric properties of ZnO thin films,which further restricts the practical application of ZnO thin films.In this paper,we utilized the magnetron sputtering,ion implantation and other technologies to obtain the ZnO:In-N films whose thickness was 250 nm on the basis of co-doping theory.The subject focused on defect regulation.The effects of annealing process on the structure,electrical and optical properties of ZnO:In-N thin films were investigated.The main achievements are as follows:First,we investigated the effects of annealing atmosphere（oxygen rich/poor）on the structure,electrical and optical properties of ZnO:In-N thin films.After ion implantation,a large number of interstitial nitrogen（N_i）defects existed in the sample,resulting in a compressive stress state in the internal tension of the sample.After high temperature annealing,a large amount of N_i is activated and diffused outward,and the grain size increases,and the internal stress is released,leading to the gradual increase of crystal quality.Compared with the anoxic annealing condition,the conductivity of the samples decreased due to the annealing in oxygen-enriched environment,and the carrier concentration further decreased with the annealing time,ranging from 10¹³ to 10¹⁵ cm^-3.Meanwhile,the resistivity of the samples increased linearly with the annealing time,which was due to the formation of a layer of high resistance adsorption film on the surface of the samples under the annealing in oxygen-enriched environment.Moreover,the concentration of oxygen vacancy related donor defects in the samples also increased significantly,which together led to the decrease of the conductivity of the samples during annealing in oxygen-rich environment.In addition,a large number of Zn_iclusters are easily decomposed into single isolated Zn_i clusters during high temperature annealing,and then spread to the surface of the sample.Among them,the diffusion rate of Zn_iIn oxygen-rich environment is significantly lower than that In anoxic environment,which may be related to the oxide film on the surface of ZnO:In-N.After annealing,the average light transmittance of the films is about 80%,and there is an obvious blue shift phenomenon in the near ultraviolet region.Second,we adopted the"step-by-step"annealing with the mode of"long time low oxygen annealing,short time oxygen rich superimposed annealing"is generally adopted at the same annealing temperature,so as to find the window of p-type conductive transformation of the sample in the short time annealing process.The reproducible p-type conductive samples were successfully prepared through many experiments,and the mechanism of p-type conductive transformation of the samples was explained.In the first stage of high purity nitrogen annealing process,a large number of intrinsic defects（such as Zn_i,V_O）are effectively suppressed,and the injected N ions are effectively activated to form N-related acceptor defects.In the second stage of oxygen-rich environment,the same sample is annealed several times,with 3 minutes as a cycle.At this stage in the process,gradually formed a layer of dense oxide film on the surface of sample,makes the acceptor defects related N not overflow the surface,at the same time,the part of the oxygen in air adsorption on the surface and a small amount of the ZnO grain boundary samples into internal to fill the position of the oxygen vacancy,further inhibiting samples within the intrinsic donor defects,so as to make the sample conduction type presents the p type,carrier concentration was maintained at 10¹⁷ cm^-3.