Research On Growth And Physical Properties Of P-type N-In Codoped ZnO Film

Semiconducting Zinc oxide has generated great interest in the past decade due to its potentials in optoelectronic applications,such as ultraviolet(UV) and blue light-emitting diodes(LED) and laser diodes(LD).With a wide band gap of 3.4eV, ZnO has a large exciton binding energy(60meV),so it can show very strong spontaneous and stimulated emissions by excitons even at room temperature,compared with 26 meV for the thermal activation energy at room temperature and 25 meV for GaN which has being widely applied for blue-ultraviolet and white light-emiting devices.However,problems associated with low solubility of acceptor dopants, self-compensation effects,and formation of undesirable deep levels have made it difficult to realize highly reliable and reproducible p-type ZnO films with excellent electronic properties,although many reports claimed realizations of p-type ZnO films and p-n homojunctions.Among possible acceptor dopants,nitrogen is a good candidate for producing a shallow acceptor level in ZnO films,and simultaneously codoping using donor(such as Ga,In,Al ) and acceptor(N) in ZnO can be expected to enhance the solubility of nitrogen and give rise to a shallower N-acceptor level in the band gap. Based on the codoping theory which has been actively studied in recent years,in the present dissertation,N-In codopedp-type ZnO films on quartz glass substrates using RF magnetron sputtering technology combining with the direct implantation of N⁺ ions are prepared successfully.The effects of thermal annealing on the structure,electrical and optical properties of the ZnO films are investigated by x-ray diffraction(XRD) via a Philips.MRD system with Cu K_αradiation(λ=0.1540597 nm),the Ecopia HMS-3000 Hall measurement system and transmission spectrum.The experimental results suggest that an appropriate annealing temperature and time play an important role in the microstructure,electrical and optical properties,especially the types of conduction of ZnO films.When the annealing temperature is in the range of 550-580℃and annealing time changes from 5 to 10min,N-In codopedp-type ZnO films can be obtained.It is noticeable that the film annealed for 20 min at 580℃exhibits the optimal p-type electrical properties with hole concentration of 1.22×10¹⁸cm^-3,hall mobility of 2.19 cm²V^-1s^-1,and low resistivity of about 2.33Ωcm,as well as good film quality among all the samples.In the case of higher annealing temperature and longer time,there is a conversion from p-type to n-type conduction of ZnO films.It is also found that all ZnO films annealed have no significant variance over absorption edge,whose wavelength is at 378nm, corresponding to energy of 3.25eV.X-ray photoelectron spectroscopy analysis confirmed the presence of nitrogen and indium in the form of N-Zn bond and N-In bond in the codoped films,and the incorporation of indium causes the change in the chemical state of nitrogen,which promotes the formation of p-type conduction.At last, to offer much more reference to optimizing the procedure of fabricating the p-type ZnO films,we draw a picture that shows the distribution of conversion of p-type conduction in our experiment.