微量Mg掺杂ZnO薄膜的光致发光光谱和带隙变化机理研究

利用射频磁控溅射(RF-MS)法在450℃玻璃基底上制备了Mg掺杂量分别为0.81at%,2.43at%和4.05at%的ZnO薄膜,对其微观结构、室温光致发光光谱(PL)、光学和电学性质进行了研究.结果发现,微量Mg掺杂ZnO薄膜晶体具有六方纤锌矿结构并保持高结晶质量;掺杂0.81at%和2.43at%Mg的ZnO薄膜室温PL谱中近带边发射(NBE)峰的短波方向出现了高能发射带与NBE峰同时存在;随着Mg掺杂量增加至4.05at%,这个高能发射带逐步将NBE峰掩盖.推测在Mg掺杂ZnO薄膜中,Mg2+替代Zn2+附近核外电子的能量增大并产生了一个高能级.而未被Mg2+替代的Zn2+周围的核外电子能量状态不变,带间能级依然存在,随着Mg掺杂量的增加处于高能级的电子数目逐步增加并占绝对优势.因此,ZnO薄膜随着Mg掺杂量增加薄膜禁带宽度增大,这是由于Mg掺杂后周围电子能量增大与Burstein-Moss效应共同作用的结果.另外,薄膜在可见光区域的平均透射率均大于85%,随着Mg掺杂量的增加,薄膜禁带宽度增大并在3.36—3.52eV内变化;Mg掺杂量为0.81at%,2.43at%和4.05at%时,薄膜电阻率分别为2.2×10-3,3.4×10-3和8.1×10-3Ω.cm.

Photoluminescence of diluted Mg doped ZnO thin films and band-gap change mechanisms

ZnO and ZnO thin films doped with different Mg contents (0.81at%,2.43at% and 4.05at%) were fabricated by radio frequency-magnetron sputtering (RF-MS) on glass substrates at 450℃.The microstructure, photoluminescence (PL), optical and electrical properties were investigated.The results show that ZnO and diluted Mg doped ZnO thin films present a hexagonal wurtzite structure with high crystal quality.In the short wavelength side of near band emission (NBE), a high energy emission band for 0.81at% and 2.43at% Mg doped thin films occurs together with NBE.The increasingly high energy band peak gradually covers the NBE peak with Mg doping increasing to 4.05at%.It is suggested that the energy of the electrons near the substituted Mg~(2+) increases, and these electrons occupy a higher energy level.However, the energy gap between conduction band and valance band still exists because the electrons energy near the un-substituted Zn~(2+) does not change.With the increasing doped Mg content, electrons in the higher energy level increase and predominate.Therefore, the reason for the increase in the band gap of Mg doped ZnO thin films can be attributed to the increase in the energy of electrons after Mg doping, together with the Burstein-Moas effect.IncidentaUy, all films exhibit a high average optical transmission (≥ 85%).The optical band gap of Mg doped ZnO thin films increases with the increasing Mg doping content and changes from 3.36 to 3.52 eV.The resistivity of the Mg doped films are 2.2 ×10~(-3),3.4 × 10~(-3) and 8. 1× 10~(-3)Ω ·cm for 0.81at%, 2. 43at% and 4. 05at% Mg contents, respectively.