The Study On The Structure And Properties Of Cr Doped ZnO Films

As a new semiconductor materials,ZnO have been attracting more attention by researchers.The lattice parameters of ZnO are a=0.32533nm,c=0.52073nm.In the wurtzite structure of ZnO,every znic atom is surrounded by four oxygen atoms.Because the surface free energy of(002)crystal face is minimum,ZnO usually grow in(002) orientation.ZnO is attractive for high efficiency short-wavelength optoelectronic nanodevices,due to its wide band gap(3.27eV)and large excitonic binding energy(about 60meV).In recent years,the transition metal(TM)-doped ZnO of diluted magnetic semiconductor become a research focus,which demonstrates the TM-doped ZnO broad application prospects.In this paper,Zn_1-xCr_xO(x=0,0.03,0.09)films were prepared by the radio frequency (RF)magnetron sputtering technique on Si(111)and quartz glass substrates,and the effects of Cr-doping on the structural and optical properties of ZnO films have been discussed.The structural properties were studied using x-ray diffraction(XRD)and scanning electron microscope(SEM)while optical properties by UV-Visible spectrophotometer (UV-Vis).XRD mezsurement revealed that the films were single phase and had wurtzite structure with c-axis orientation.With the increase of Cr concentration,the intensity of the (002)peak and the particle size of the Zn_1-xCr_xO(x=0,0.03,0.09)films became decreased, and the Full Width at Half Maximum(FWHM)of(002)peak,the crystal lattice parameter c of Zn_1-xCr_xO(x=0,0.03,0.09)films and the width of optical band gap became increased, respectively.In the transmittance spectra of the Zn_1-xCr_xO(x=0,0.03,0.09)films the movement of the absorption edge of ultraviolet region is the Burstein-Moss shift with the increase of Cr concentration.At the same time,we found the band gap Eg of film also increase as a result.From the PL spectrum of the sample we found the PL peak at 392nm(arise from exciton recombination)decreased with Cr doped.And for the PL peak at 420nm moved to short wavelength with increasing Cr concentration.We thought that:(1)Since the elements Cr doped,the band gap energy changed,which may lead to the free exciton of ZnO film disappear,which made the nearly 392 nm UV luminescence peaks disappeared.(2)With the increase of the Cr content,the film grain size became smaller,the quantum effect became enhanced,so the peak at 419 nm was in the blue shift.From the M-H picture,we can see clearly that the Zn_1-xCr_xO(x=0.03,0.09)samples showed magnetic property under the condition both of 5K and 300K.We found the magnetization became smaller with increasing Cr concentration,and the magnetization at RT(T=300K)is smaller than low-temperature(T=SK).We thought that the magnetization rooted in dual-exchange mechanism which Cr ions systematically substituted for the Zn ions in the films.