Mo Xiaoming, Fang Guojia, Long Hao, Li Songzhan, Wang Haoning, Chen Zhao, Huang Huihui, Zeng Wei, Zhang Yupeng, Pan Chunxu
School of Physics and Technology, Key Lab of Artificial Micro- and Nano-Structures of Ministry of Education, Wuhan University, Wuhan 430072, People's Republic of China.
Phys Chem Chem Phys. 2014 May 28;16(20):9302-8. doi: 10.1039/c3cp55505d.
Light-emitting diodes (LEDs) based on n-ZnO@i-MgO core-shell (CS) nanowires (NWs) are herein demonstrated and characterized. MgO insulating layers were rationally introduced as shells to modify/passivate the surface defects of ZnO NWs. A high-quality ZnO/MgO interface was attained and the optically pumped near-band-edge emission of the bare ZnO NWs was greatly enhanced after cladding i-MgO shells. Electroluminescence (EL) spectra measured in the whole UV-visible range revealed that light emission can only be detected when LEDs were applied with reverse bias. Moreover, the emission color can be tuned from orange to bright white with increasing reverse bias. We explored these interesting results tentatively in terms of the energy-band diagram of the heterojunction and it was found that the interfacial i-MgO shells not only acted as an insulator to prevent a short circuit between the two electrodes, but also offered a potential energy difference so that electron tunneling was energetically possible, both of which were essential to generate the reverse-bias EL. The dipole-forbidden d-d transitions by the Laporte selection rule in the p-NiO might be the reason to why there is no light being detected from the CS NW LED under forward bias. It is hoped that this simple and facile route may provide an effective approach in designing low-cost CS NW LEDs.
本文展示并表征了基于n-ZnO@i-MgO核壳（CS）纳米线（NWs）的发光二极管。合理引入MgO绝缘层作为壳层，以修饰/钝化ZnO NWs的表面缺陷。获得了高质量的ZnO/MgO界面，包覆i-MgO壳层后，裸ZnO NWs的光泵浦近带边发射得到了极大增强。在整个紫外-可见光范围内测量的电致发光（EL）光谱表明，只有在对发光二极管施加反向偏压时才能检测到发光。此外，随着反向偏压的增加，发射颜色可从橙色调至亮白色。我们根据异质结的能带图初步探讨了这些有趣的结果，发现界面i-MgO壳层不仅起到绝缘体的作用，防止两个电极之间短路，还提供了势能差，使得电子隧穿在能量上成为可能，这两者对于产生反向偏压电致发光都是必不可少的。p-NiO中由拉波特选择规则禁止的偶极d-d跃迁可能是在正向偏压下从CS NW发光二极管中未检测到光的原因。希望这种简单易行的方法能为设计低成本的CS NW发光二极管提供一种有效途径。
