Co掺杂对ZnO晶体中光生电子瞬态过程的影响

采用气相反应制备了ZnO和ZnO∶Co微晶,并通过热释光研究了材料中的电子陷阱能级(施主能级),采用微波介电谱研究了材料的光生电子瞬态过程.发现纯ZnO热释光谱有两个峰,分别为-183 ℃和-127 ℃,说明存在两个电子陷阱能级;而ZnO∶Co中热释光信号很弱,只有纯ZnO的十分之一.微波介电谱研究表明,由于电子陷阱对导带电子的驰豫作用,纯ZnO材料导带光电子的衰减为一级指数过程,寿命为802 ns.ZnO∶Co微晶体的最大微波介电谱强度低于纯ZnO晶体的五分之一,电子陷阱密度较小,其光生电子快速衰减,过程仅为10～20 ns.结果说明Co掺杂具有明显的抑制电子陷阱能级生成的作用.

Effect of Co Doped on the Photoelectrons Decay Process of ZnO Crystal

ZnO and ZnO∶Co microcrystal were prepared by gas phase reaction.The electron trap energy level structure (donor level) and the photoelectrons temporal process of materials was investigated by thermo-luminescence microwave and absorption dielectric spectrometry respetively. Two peaks was observed in thermo-luminescence spectra of pure ZnO, one is -183 ℃ and the other is -127 ℃, which shows that two kinds of electron trap energy level produced by the intrinsic defects in ZnO. The thermo-luminescence intensity of ZnO∶Co was only 10% of pure ZnO, which shows that the consistency of electron trap is very less. The microwave absorption dielectric spectrometry shows the temporal process of photoelectrons in conduction band in pure ZnO decayed according to exponential, the lifetime of phase photoelectrons is 802 ns. The reason of long lifetime is relaxation effects of electron trap to conduction band photoelectrons. The microwave absorption dielectric spectrometry relative intensity of ZnO∶Co less than one-fifth of the pure crystal ZnO, that shows the density of electron trap is less in ZnO∶Co minicrystal, so photoelectrons are disappeared quickly, and the decay process of photoelectrons is only 10-20 ns. The results show that Co doped ZnO have obvious effect on restrain the formation of electron trap energy level.