The bipolar doping of ZnS via native defects and external dopants

By employing first-principle total-energy calculations, a systematic study of the dopability of ZnS to be both n- and p-types compared with that of ZnO is carried out. We find that all the attempted acceptor dopants, group V substituting on the S lattice site and group I and IB on the Zn sites in ZnS, have lower ionization energies than the corresponding ones in ZnO. This can be accounted for by the fact that ZnS has relative higher valence band maximum than ZnO. Native ZnS is weak p-type under S-rich condition, as the abundant acceptor V-Zn has rather large ionization energy. Self-compensations by the formation of interstitial donors in group I and IB-doped p-type ZnS can be avoided when sample is prepared under S-rich condition. In terms of ionization energies, Li-Zn and N-S are the preferred acceptors in ZnS. Native n- type doping of ZnS is limited by the spontaneous formation of intrinsic V-Zn(2-); high efficient n-type doping with dopants is harder to achieve than in ZnO because of the readiness of forming native compensating centers and higher ionization energy of donors in ZnS. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3103585]

交通战备保障方案决策系统的研究设计

阐述了一种交通战备保障方案实施决策支持系统，介绍了系统的数据库系统、模型库系统的设计.该系统主要针对突发事件，为交通战备保障方案的实施提供快速、有效的决策支持。