MOCVD Growth And In-situ Doping Of High Quality ZnO Films

ZnO has an exciton binding energy of 60MeV, and it is a new emiconductor material with superior optical and electrical properties, which has great potential applications in the ultraviolet detectors and lasers. However, p-type ZnO doping problem has already become a great obstacle for the further development of ZnO material.Currently the N-doping ZnO is recognized as the most promissing way to achieve stable, efficient p-type ZnO, so we want to study the behavior of N-doped ZnO donor and acceptor in detail as well as in the annealing process, We are willing to see that our work provide some new idea to the realizing of p-type ZnO.The polarity of ZnO has significant impact on the growth kinetics properties, electrical properties, optical properties, At the same time it also has significant influence on the ZnO p-type doping.We must regard the polarity of the ZnO as an important factor if we want to abtain high quality ZnO samples. Different polarity of the ZnO single crystal material under different pretreatment condition may lead to different results, so we study the effect of different pretreatment temperature on the material.As the global environmental problems is increasingly ourstanding, the access to clean energy has been pursued all the time. The transformation of the solar energy into electrical energy through photovoltaic cells is a very reliable solution. Intermediate band solar cell is a promissing method to obtain clean energy with low economic cost and high efficiency, so we have a attempt on this aspect.The main results of this paper are as follows.1 We have grown high quality N-doped ZnO films on ZnO template substrate through MOCVD method, using NH3 as the N doping source. A detailed study of the behavior of the zni has been carried out during annealing process. N occupy the O sites(No) is a possible acceptor, and N occupy the Zn sites(Nzn) becomes a possible donor. No-Zni complex and Zni clusters is the main compensating donor in ZnO:N. No is gradually desorpted during the process of annealing, for the separate zni is not stable. Zni in the No-Zni complex gradually begin to accumulate and more stable zni clusters is formed. For the further increased annealing temperature, Zni clusters also begins to decomposition and escape from annealed films.In addition, the acceptor is successfully activated during the rapid thermal annealing,which is observed in the C-V measurement, the n-type ZnO changes into p-type after theprocess of anealling.2 we have grown high quality ZnO on Zn face and O face single crystal substrate through MOCVD method, the substrate is dealt with different temperature pretreatment. The AFM measurement shows that the Zn-face sample has a more smooth surface and smaller roughness. We can see that samples grown on Zn-face have an advantage to suppress the non intentionally doped carbon in the Raman spectra. The PL spectra results also shows that Zn surface samples has a stronger the band edge peak intensity, and Zn face growth is also important to the realization of P type doping. Generally speaking, Zn surface growth has a better performance of the ZnO in all aspects.The 1100℃ temperature for substrate pretreatemeat is too high for ZnO homoepitaxy growth, the surface polarity of the sample is ruined, so that is not good for ZnO homoepitaxy growth, Zn-face growth with a pretreat tempmperature of 1000℃ is the most suitable condition.3 For now, the dominate method of the synthesis of solar cell materials is non equilibrium state growth like PLD method, which destroys the crystal lattice structure and deteriorates the performance of the material. We have successfully grown ZnTe:O alloys using equilibrium MOCVD method. Further more, we developed a face-to-face annealing method to improve the property. In the XPS spectrum we can see that the O atoms may take the Te sites or the Zinc sites, it may also be acted as the interstitial O. The PL spectrum shows that the C sample has an obvious luminescence peak at the energy level of 1.9eV, which is regarded as the middle band of oxygen. So it provides new ideas and possibilities for the research of solar cell materials.