Deposition And Ion Implantation Of ZnO Thin Films

In this thesis, ZnO and ZnMnO thin films have been prepared by reactive ionized cluster beam, magnetron sputtering and pulsed laser deposition. Ion implantation with different elements and different dose is used to dope the films. Finally a series of analysis and research have been carried out on the structure, composition,optical and magnetic characterization.1. Deposition of ZnO films. Reactive ionized cluster beam (RICB) is used to prepared ZnO Thin Films. We design the RICB system and in the system, we use a Hall ion sourse, add an ultrasonic crucible and a gas introduction holl, on the basis of these, a set of RICB has been combined. X-ray diffraction (XRD) and EDS energy spectroscopy are used to test and analyse the samples. Results show that films are of wurtzite structure along the C-axis orientation growth characteristics and better crystal quality, while the atomic ratio of ZnO thin films is close to 1:1.ZnMnO films are deposited on silicon Si (111) substrates by magnetron sputtering, sputtering targets are ZnO:Mn (Mn weight ratio is 5%). Mn oxides form is not be found in the XRD spectra, indicating that Mn has substituted Zn lattice position. XPS spectra of the ZnMnO films indicate the dominant oxidation state is Mn2+. And the XPS spectra reveal that Mn as dopant substitutes the lattice position of Zn and there are no excessive Zn exiting in the Mn-doped ZnO film. The peaks of ZnMnO film Raman scattering are all the ZnMnO characteristic peaks. MnO, Mn3O4 or MnO2 are not found in Raman spectra, Indicating that there are no other Mn oxides in our ZnMnO samples.2.Ion implantation doping of ZnO film. ZnO films were grown on Si (111) by pulsed-laser deposition. Doping was conducted by 200 keV Sb implantation to total doses of×1013,5×1014, 1×1015,1×1016cm-2. Rapid thermal annealing was carried out at temperatures of 400,500,600℃for 30 s in a flowing oxygen atmosphere. When the implantation dose is lower, the peak at 576 cm-1 experiences an increase and has an asymmetric shape with a shoulder centered at 550 cm-1. This is attributed to ion-induced damage to the lattice, since this asymmetric band has been eliminated after the rapid thermal annealing. We found that to completely remove the defects, an annealing temperature of 600℃is necessary. When implantation dose is higher, in the Raman spectra of ZnO thin films, the peak at 576 cm-1 is enhanced and half width (FWHM) also increased. After thermal annealing, the recovery of lattice damage is very weak and found that annealing to improve the 576 cm" peak FWHM and lower non-symmetric peak has no apparent help. This shows that high doses of ion implantation resulted in serious injury lattice, Sb ions to this concentration,576 cm-1 peak corresponding to the wave vector surface of the crystal lattice structure damage have been more serious. Through comparisons of the different doses of the sample can be clearly seen,576cm-1 peak with the Sb ion implantation dose increases, the peak height increased, the FWHM broadening, asymmetry of the more obvious. In the Sb ion implantation in ZnO films PL spectrum there is 3.230 eV peak, and it is not observed in un-doped samples. This may be caused by the Sb ion implantation, and Sb as acceptors exist in the films. The PL peaks intensity of all Sb ion implantation samples have changed, and the peak of 3.365 eV relative to the peak of 3.331 eV peak has been enhanced, but all of the peaks relative to the un-doped samples were weakened, indicating that high energy ion implantation effects on the optical properties of ZnO.ZnMnO films were grown on Si (111) by magnetron sputtering. Doping was conducted by 200 keV Sb implantation to total doses of 5×1013,5×1014, 1×1015, 1×1016 cm-2. In the XPS spectra of ZnMnO films, The typical Ols peak in the surface can be fitted two peaks by nearly Gaussian functions. The Zn 2p3/2 peak is situated at 1021.3eV, showing that Zn ion in the films are mainly in the chemical states of Zn2+. The core level spectrum of Zn 2p3/2 shows good symmetry. These results indicate that there is little excessive zinc existing in the films. Mn 2p2/3 XPS spectra for the ZnMnO films located at about 642.1 eV. This is the peak position of the binding energy of Mn2+ oxid. Mn as dopant substitutes the lattice position of Zn in the Mn-doped ZnO film. The symmetry indicates a single bonding state of Mn in ZnMnO films. In the X-ray diffraction pattem of the Sb-implanted ZnMnO films, (101) peak is very weak and one amorphous zone can be observed near the 40°, it is obviously due to the mismatch of lattice caused by ion bombardment.3. Transition metal ion implantation and magnetism research. ZnO films were grown on Si (111) by pulsed-laser deposition. Doping was conducted by 200 keV Sb implantation to total doses of 1x1015,5x1015,1x1016,5x1016 cm-2. The 2θvalues of (002) peaks are in the range of 34-35°:the peak of the ZnO epilayer is located at 34.62°. The value of the implanted ZnO is at 34.47°. After annealing at 400,550and 700℃, the peak moves to 34.65,34.76 and 34.67°respectively. Changes in the diffraction angle and full width at half maximum (FWHM) of the prominent (002) peak are observed in samples implanted with different Mn doses. Both the A1 (LO) and E2 (high) modes of the as-implanted ZnO film are broadened and shifted towards the low-frequency side, compared with the values of bulk ZnO. This is attributed to ion-induced damage to the lattice. In addition, two additional phonon modes at 619 (I1) and 642 cm-1 (I2) were observed in ZnO:Mn thin films,which were ascribed to local vibration modes due to dopant-related complexes or to host defects. The surfaces of the as-deposited ZnO and implanted ZnO:Mn thin films were investigated using AFM. It is clearly seen that the surface of implanted ZnO tends to be compact and homogeneous and quite different from that of the as-deposited sample; micro-particles are dispersed evenly throughout the modified surface, whereas no such small particles appear on the as-deposited sample. For the annealed sample implanted with Mn+ ions dose above 1×106 cm-2, we notice numerous clusters with a regular shape and uniformly distributed in the sample. We also measured the root mean square (RMS) roughness and the results showed that the RMS roughness decreased from 29.9 nm to 51.5 nm when the implantation dose of Mn increased from 1×1015 to 5×1016 ions/cm2. The PL spectrum of as-deposited ZnO consists of strong near-band edge (NBE) emission peak at 3.25 eV; no yellow or green emission peaks due to ionized oxygen vacancy or interstitial atoms are observed. This indicates the good crystalline quality of the as-deposited ZnO films. In the Mn implanted ZnO film, however, we observe a yellow band around 540 nm. The near-bandedge emission position is also shifted to lower energy, which can be attributed to strain induced by the incorporation of Mn ions, which have a larger ionic radius than Zn and would expand the lattice when substituting Zn sites. Magnetization loops of the implanted ZnO:Mn films were measured at room temperature with the magnetic field being applied parallel to the surface of the samples. The hysteresis loop was measured at 300K of the magnetic ZnO:Mn with Mn implantation dose of 5×1016 ions/cm2. The magnetization of the sample is saturated for fields higher than 2 kOe at 300 K. In our experiment, a maximum remnant magnetization is observed in samples with 5 mol% Mn. Since the possible secondary phases like MnO and MnO2 were not observed, it is understood that the observed magnetic behavior in ZnO:Mn films are not due to formation of the manganese oxides.