Study Of The Growth And Photoelectrical Properties Of Al-N Codoped ZnO Thin Films

ZnO is a ?-? direct band gap semiconductor material with a wide band gap of 3.37 eV.It has a large exciton binding energy of 60 me V at room temperature,much higher than the thermal ionization energy(26 me V).This makes it possible to achieve exciton luminescence at room temperature.So ZnO has been taken as a promising material for more efficient UV-optoelectronic devices.To realize its application,the most important issue is the fabrication of n and p type ZnO with a high carrier concentration and low resistance.It has obtained n-type ZnO with high electron density.However,it is very difficult to obtain p-ZnO with good characteristics.Therefore,the preparation of stable p-type ZnO films with high hole density has become a bottleneck for realizing ZnO-based optoelectronic devices.So far,many efforts have been done to fabricate p-type ZnO by using group-? and group-? elements.However,it is found that this method created a rather deep accepter level and a low solubility of accepter dopants.To solve those problems,a co-doped method using group-? and group-? dopants was proposed to prepare p-type conduction.This can reduce the formation energy of acceptors and decrease the binding energy of the acceptor.In this thesis,we chose Al and N as the co-doping elements to investigate the optical and electrical properties of Al-N co-doped ZnO.Finally,p-type ZnO has been obtained by annealing experiment.The N doped and Al-N co-doped ZnO were prepared by thermal oxidation method.Zn3N2 and Zn3N2:Al were fabricated as precursors by magnetron sputtering and annealed in oxygen atmosphere at diffident temperature.The results showed that the temperature in which the Zn3N2 begin to transmit to ZnO was lower than Zn3N2:Al.The crystal quality of Al-N co-doped ZnO was better than N doped ZnO.The Al-N co-doped ZnO had a preferred orientation of(002)while the N doped ZnO had a multiphase structure after thermal oxidation.All of the films showed high transmittance in the visible region and strong absorption in the near UV region.The exciton absorption still exist at 900 ? in Al-N co-doped ZnO thin films much higher than N doped ZnO,indicating that Al-N co-dope could improve the stability of ZnO.The Al-N co-doped ZnO showed p type at the anneal temperature over 600 ?.We also studied the influence of substrate temperature and the N2 pressure on the properties of Al-N co-doped ZnO prepared by co-sputtering method.The result showed that all the films showed(002)preferred orientation.With the increase of the temperature,the angle of(002)diffraction peak increased from 34.170 ° to 34.214 ° and the full width at half maximum decreased from 0.452 °to 0.411 °,indicating that the crystalline quality became better.The electron concentration increased from 1.582×1017 cm-3 to 4.188×1018 cm-3 with the increase of substrate temperature.All the films showed high transmittance in the visible region.The electron concentration of Al-N co-doped ZnO thin films deposited at different N2 pressure showed obviously lower than none N2.In order to activate the acceptor defects related to N and reduce the concentration of donor defects,the Al-N co-doped ZnO thin films were annealed at 500 ?,600 ?,700 ?.The films showed p-type at 700 ?.