Preparation Of N Doped P-type Mg_xZn_1-xO Thin Films And Research On Related Problems

Since the structure and optoelectronic properties of MgxZn(1-x)O alloy with wurtzite structure are very similar to ZnO and the band gap of MgxZn(1-x)O can be tuned, Mg-Zn-O alloy was proposed as a ZnO barrier layer. Now, n-type MgZnO with high crystal quality can readily be prepared, but fabrication of p-type MgZnO with good stability and electrical properties is still a difficult task. Some research groups have made many efforts to prepare p-type MgZnO by using N as acceptor dopant. However, it is hard to fabricate reproducibly N-doped p-type MgZnO with low resistivity, high carrier concentration and high mobility, due to low solubility of N in MgZnO and self-compensation of (N₂)o and other native donors for No acceptors. Obviously, it is very important to increase the solubility of No and decrease the self-compensation of (N₂)o for obtaining N-doped p-type MgZnO. Therefore, it is interesting to characterize chemical state and solubility of N in N-doped MgZnO correctly and simply and understand effect of Mg on the chemical state and solubility. In this thesis, a detailed investigation according to the present research difficulties on MgZnO has been carried out, and the following results are obtained:(1) N doped ZnO films were prepared on quartz substrates by r.f. magnetron sputtering method using ZnO target, with mixture of nitrogen and argon as sputtering gas. The effects of change of the flux ratio of N₂/(N₂+Ar) of sputtering gases on structure and properties of ZnO alloy thin films were investigated. when the flux ratio of N₂/(N₂+Ar) is 20%,the film of best p-type conductivity property has resistivity of 20.54Ωcm, Hall mobility of 5.69cm2/Vs and carrier concentration of 5.49x 1016 cm^-3. With the flux ratio of N₂/(N₂+Ar) increasing, the band-gap width occurs red shift.(2) N doped MgZnO films were prepared on quartz substrates using Mgo.04Zno.96O target, with mixture of nitrogen and argon as sputtering gas. The film of best p-type conductivity property has resistivity of 21.47 Qcm, Hall mobility of 3.45cm2/Vs and carrier concentration of 8.38×1016cm^-3, when the nitrogen partial pressure ratio is 20%. The p-type behavior of the film was confirmed by p-MgZnO/n-Si heterojunction which showed a clear p-n diode characteristic.The effects of annealing temperature on the structure and properties of MgZnO:N films were studied. We found that with the increasing annealing temperature, the crystallinity is improved, the conductivity of the film changed dramatically from n-type to p-type, and finally changed to weak p-type.At an intermediate annealing temperature 600℃, the N doped MgZnO film behaves the best p-type conductivity property.(3) N doped MgxZn(1-x)O films were prepared on quartz substrates using ZnO, Mg0.04Zn0.96O and Mgo.08Zno.92O targets, respectively, with mixture of nitrogen and argon as sputtering gas. The solubility and chemical state of N in these films were studied. The solubility of No decreases with increasing Mg concentration. The chemical state of N in the MgZnO:N films is affected by Mg concentration.It can be changed from coexistence of No and (N₂)o in the MgZnO:N with low Mg concentration to only (N₂)o in the MgZnO:N with high Mg concentration.(4) The Raman spectra of ZnO:N and MgZnO:N were studied. The additional Raman peaks are observed at about 272 and 642 cm-1 in the ZnO:N films Raman spectra and the intensity of the additional peaks and 580 cm-1 peak increases with increasing the flux ratio of N₂/(N₂+Ar). Raman spectra of the N-doped ZnO and MgxZn(1-x)O produced by the mixed gas with a fixed flux ratio indicate that the intensity of 272,642 and 580 cm-1 peaks decreases with increasing Mg concentration,and the XPS spectra of Nls of these films indicate No solubility decreases with increasing Mg concentration. So,the characteristic Raman peaks related to N doping observed in the N-doped ZnO and MgxZn(1-x)O at 272,642 and 580 cm-1, respectively, are demonstrated to be only related to No but not to...