Preparation Of ZnO Crystal And Study Of The Composite Defects Influence On The Electronic Structure And Optical Propertise Of ZnO Crystals

As development of the application of ZnO, the preparation of ZnO crystals and the defects of ZnO have been gained extensive attention. The study of the defects of ZnO crystals by the theory method provides that the theory basis for the preparation of ZnO crystals, doping of ZnO crystal research and the transformation of the p type of ZnO crystals. It has the vital significance for the use of the semiconductor that understand the intrinsic defects in ZnO crystals. The electronic structure and optical properties of the composite defect ZnO crystals has been studied by first-principles in this paper. The concrete contents are as follows:1. The size of ZnO crystal is about Φ 4 mm x 5 mm. The ZnO crystal has hexagonal wurtzite structure. The C axis preferred orientation and crystallinity of ZnO crystals is better. It is show that the ZnO have better quality, lower impurity components. But there are impurities such as Al, Ga in ZnO crystals.2. Three composite defect models were build: one Al atom occupied one Zn atom position respectively with interstitial Zn, Zn vacancies, O vacancies（Al ZnZni）,(AlZnV_Zn),（AlZnVO）. Discussed the electronic structures and optical properties of three composite defect ZnO crystals.The calculation results show that the volume of ZnO crystal has been increased by the intruduction of AlZn Zni composite defect, while the AlZn VO and Al ZnV_Zn composite defects lead the volume of ZnO crystal to reduction. The calculation of defect formation energy show that Al ZnZni composite defect more easily formed in ZnO crystal compared to the other two composite defects. The band diagram and the electronic density of states can be seen that the Al_ZnZn_i composite defect has the greatest influence that introduce the excess surplus electronics in the bottom of the conduction band. The Al ZnZni composite defect also lead the whole band of ZnO crystal to move down, the Fermi level into the conduction band, and ZnO crystal shows the characteristics of degenerate semiconductor. The Al_ZnZn_i and AlZnVO composite defects contribute to a n-type semiconductor formation of ZnO crystal. The AlZnV_Zn composite defect lead the band gap to an increase of ZnO crystal. The influence of three kinds of composite defects on ZnO crystal is mainly in the low energy range. The Al Zn Zni and AlZnVO composite defects lead the imaginary part of the dielectric function at 4.52 eV to red shift, and an increases of the peak value.3. Three composite defect models were build: Zni, VO, V_Zn respectively with Ga impurity(Ga ZnZni, Ga_Zn VO, Ga_ZnV_Zn three composite defects). The calculation results show that the Ga_ZnZn_i composite defect lead the ZnO crystal volume to an increased. The Ga_Zn VO and Ga_Zn V_Zn composite defects lead the volume of ZnO crystal to reduce. The Ga_ZnZn_i composite defect is more likely to form in ZnO crystal compared with other two kinds of composite defects. The Ga_Zn Zni and Ga_ZnVO composite defects also contribution to a n-type semiconductor formation of ZnO crystal. The Ga_Zn Zni, Ga_Zn VO and Ga_Zn V_Zn composite defects all introduced the isolation level between the end of the bottom of the valence band and the valence band. The Ga_ZnZn_i and Ga_ZnVO composite defects lead the imaginary part of dielectric function of ZnO at 4.52 eV peak to move towards the low energy rang, and the peak intensity increased significantly.