慢正电子对ZnO中本征缺陷的研究

Native defects in ZnO films studied by slow positron beam

利用慢正电子研究了不同氧含量时射频磁控反应溅射制备的ZnO样品,观察到ZnO中本征缺陷(VO,VZn)随混合气体中O2比例(PO2)的变化关系。结果表明:PO2≤70%时,这些ZnO样品中存在同一种缺陷类型,O空位(VO)和Zn填隙(Zni)可能是材料中主要缺陷。PO2>70%时,这些ZnO样品中缺陷以Zn空位(VZn)为主。随着反应室中O2含量的增加,样品的Zn空位(VZn)浓度逐渐增加;当PO2为85%时,与正电子湮没的VZn数目减少,可能是杂质原子对VZn屏蔽引起的结果;PO2低于50%,材料中H原子数目相对较多,H原子会与晶格中的悬挂键结合,和存在同种缺陷的其它样品相比,这时能与晶格原子悬挂键湮没的正电子数目要减少很多。随着O2含量增加,VZn浓度逐渐变大,VO和Zni浓度相应减小,这些变化与光致发光谱(Photoluminescence,PL)反映的实验结果相吻合。

Native defects in ZnO films grown by radio frequency （RF） reactive magnetron sputtering under variable oxygen fraction conditions have been investigated by using monoenergetic positrons beam technique. The results show that the same type defects dominate in these ZnO samples grown at oxygen fraction less than 70% in the process chamber; and zinc vacancies are preponderant in the ZnO films fabricated in richer oxygen environment. The concentration of zinc vacancies increases with oxygen partial fraction rising. While oxygen fraction reaches 85%, zinc vacancies that could trap positrons decrease, which suggests that impurities could shield zinc vacancies. A combination between hydrogen atoms and the dangling bonds in the lattice could weaken the trap of positrons under the 50% oxygen fraction condition. The concentration of zinc vacancies varies in different oxygen fraction films, which is in agreement with the conclusion of photoluminescence spectroscopy.