Study On P-type Conduction Mechanism And Photoelectric Characteristics Of N-Ion Implanted ZnO

As a wide bandgap semiconductor material with direct band gap,ZnO has excellent photoelectric properties and its exciton binding energy is as high as 60 meV,which has great application potential in short-wavelength optoelectronic devices.To realize the application of ZnO in short-wavelength optoelectronic devices,it is necessary to simultaneously prepare high-quality n-type and p-type ZnO.Due to the large amount of intrinsic defects of ZnO and the self-compensation effect of impurities,n-type ZnO is easily obtained,and p-type ZnO is difficult to realize.In the past ten years,researchers from all over the world have invested a lot of energy in the research of p-type doping of ZnO,and made remarkable progress.However,at present,there is no clear understanding of the acceptor microscopic morphology and formation process of p-type ZnO.The conductivity and stability of p-type ZnO cannot meet the requirements of the device.Because the ionic radius and electronegativity of N is very similar to O,it are considered to be the most suitable acceptor doping elements for p-type ZnO.In this thesis,N-doped ZnO is used as the research object.N-ion implanted ZnO thin film/single crystal is used,and the defects are controlled by annealing.XRD,Hall,Raman,XPS,SIMS,PL,EPR and other test methods are used to study the microstructure,electrical conductivity,luminescence properties and doping concentration of N in ZnO film/single crystal under N ion implantation and different annealing conditions.And the doping morphology,the p-type conduction mechanism of N-doped ZnO is deeply analyzed.Through a series of research work,the following main results were obtained:?1?The ZnO thin films were annealed in an oxygen-rich,nitrogen-rich and zinc-rich atmosphere by rapid annealing.The results showed that the carrier concentration of the ZnO thin films did not change significantly after annealing in N ₂atmosphere,and decreased by an order of magnitude after annealing in O₂ atmosphere.And after annealing in the Zn vapor atmosp here,two orders of magnitude were added.At the same time,combined with photoluminescence?PL?and electron paramagnetic resonance?EPR?measurements,it was found that zinc vacancies(V_Zn)are the main compensatory defects of the carriers of ZnO thin films,and the composite defects of interstitial zinc?Zn_i?and oxygen vacancies?V_O?are the main donor sources for n-type conductivity of undoped ZnO thin films.?2?ZnO films with different N ion implantation doses were annealed at different temperatures in N₂ atmosphere.The samples implanted at a dose of 5×10¹⁶ cm^-2achieved p-type conductivity at an annealing temperature of 850°C-900°C.When annealing at 900°C,the N-doped ZnO film exhibited the best p-type conductivity,and after three months,the hole concentration did not decrease significantly.The p-type conduction mechanism of N-doped ZnO thin films was investigated by Raman,XPS and low temperature PL.The experimental results show that the shallow acceptor level at 161 meV above the top of the valence band is attributed to the V_Zn-N_O acceptor complex.The formation of the V_Zn-N_O acceptor complex and the elimination of Zn_i-related shallow donor defects during annealing are the reason for the p-type conductivity transition of N-doped ZnO thin films.?3?N-doped ZnO single crystal bulks have been prepared by ion implantation.The effects of different annealing temperatures on the structure and optical properties of the samples have been investigated.The behavior of defects in N-doped ZnO single crystals has been also explored.The annealing can restore the lattice disorder caused by ion implantation to some extent,but the concentration of N in ZnO decreases as the annealing temperature increases.Compared with the intrinsic ZnO single crystal bulk,the two main luminescence peaks at 3.105 eV and 3.220 eV appeared in the low temperature PL spectrum of the annealed sample.The former is attributed to electronic transitions from the conduction band to the Zn vacancy(V_Zn)acceptor level,while the latter is attributed to the donor-acceptor pair?DAP?complex.The experimental results show that proper annealing treatment can induce N-doped ZnO materials to form more effective acceptor?N_O?and V_Zn intrinsic acceptors.The interaction of V_Zn and N_O will lead to the transformation of ZnO material conductivity types.