Study On The Preparation Of ZnO Films By High Power Impulse Magnetron Sputtering

Zinc oxide?ZnO?is one of the most popular semiconductor materials with hexagonal crystal structure.The two most important properties of zinc oxide are direct and wide bandgap?3.37 eV at room temperature?and the high excitation energy?60 meV?.These properties make ZnO widespread applications in photoelectric devices,solar cells and ferroelectric devices and so on.The high power impulsed magnetron sputtering?HiPIMS?technique has the characteristics of high density and high ionization rate.Therefore,HiPIMS has obvious advantages over traditional dcMS.In this work,ZnO thin films are prepared by HiPIMS.The crystal structure,surface morphology and electrical properties of the films are studied.The plasma charcteristics are diagnosed by time-resolved emission spectroscopy.The main research contents and conclusions are as followings:1.The O₂/Ar ratio influences the structures and electrical properties of ZnO thin films in HiPIMS.We find that the O₂/Ar ratio dominates not only the ZnO crystallinity but the film electrical properties.The c-axis preferential?002?ZnO can be grown in HiPIMS even there was no external heating.By the temporal resolution OES it is noted that the intensities of species in OES increases with increase of O₂/Ar ratio,especially in O₂/Ar=14/80 sccm,the densities of Ar⁺and Zn⁺are significantly increased.We deduce that the Penning discharge is improved in the HiPIMS.It is evidence by the measurement of film growth rate:the higher oxygen partial pressure,the larger deposition rate.2.The pulse width affects the properties of n-Zn O films.It is found that the crystallinity of Zn O is relatively good when the pulse width was 60?s and 70?s.This is because the energy of the sputtered particles are suitable for nucleation and growth.When the pulse width is greater than 50?s,the intensities of Zn?and Zn?basically remain unchanged after 20?s later of the discharge begining,but the O?decreases with time.This may lead to the increase of zinc interstitial,so the carrier concentration is relatively high at 60?s and 70?s.3.The deposition temperature plays a critical role on properties of ZnO thin flms by HiPIMS.It can be seen from AFM images that when the deposition temperature is 300?,the Ra value of the ZnO film is the smallest.In SEM images Zn O films deposited at 300?have the characteristics of uniform particle size and compact structure.The results of Hall effect test also show that the carrier concentration and mobility of the ZnO films prepared under300?are high,and the resistivity is small.Therefore,we can conclude that the morphology and electrical properties of ZnO films are closely related to the substrate temperature.4.The O₂/Ar/N₂ ratio,deposition temperature and assisted ICP power affect the properties of p-ZnO films prepared by HiPIMS.It is obtained that the electrical properties of ZnO thin films prepared at room temperature are the best when the N₂ flow rate is 8sccm.In the first 5 testings the sample demonstrates p-type,and the carrier concentration reaches E+16 cm^-3.At a low substrate temperature,the compact ZnO films composed of small particles,the electrical properties are better.The probability of ZnO tuning to a p-type can reach 80%,the carrier concentration can reach E+15 cm^-3.With an assited ICP,it is found that the addition of ICP increases the activity of atomic O and oxidationability of thin films,which leads to the decrease of No defects,and not enhancement of electrical properties of Zn O thin films.