Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan.
ACS Appl Mater Interfaces. 2011 Nov;3(11):4415-9. doi: 10.1021/am201062t. Epub 2011 Oct 13.
Room-temperature ultraviolet (UV) luminescence was investigated for the atomic layer deposited ZnO films grown on silicon nanopillars (Si-NPs) fabricated by self-masking dry etching in hydrogen-containing plasma. For films deposited at 200 °C, an intensive UV emission corresponding to free-exciton recombination (~3.31 eV) was observed with a nearly complete suppression of the defect-associated broad visible range emission peak. On the other hand, for ZnO films grown at 25 °C, albeit the appearance of the defect-associated visible emission, the UV emission peak was observed to shift by ~60 meV to near the direct band edge (3.37 eV) recombination emission. The high-resolution transmission electron microscopy (HRTEM) showed that the ZnO films obtained at 25 °C were consisting of ZnO nanocrystals with a mean radius of 2 nm embedded in a largely amorphous matrix. Because the Bohr radius of free-exictons in bulk ZnO is ~2.3 nm, the size confinement effect may have occurred and resulted in the observed direct band edge electron-hole recombination. Additionally, the results also demonstrate order of magnitude enhancement in emission efficiency for the ZnO/Si-NP structure, as compared to that of ZnO directly deposited on Si substrate under the same conditions.
室温下的紫外（UV）发光被研究了原子层沉积在硅纳米柱（Si-NPs）上生长的 ZnO 薄膜，这些硅纳米柱是通过含氢等离子体自掩模干法刻蚀制备的。对于在 200°C 下沉积的薄膜，观察到了与自由激子复合（~3.31 eV）对应的强 UV 发射，同时几乎完全抑制了与缺陷相关的宽可见光发射峰。另一方面，对于在 25°C 下生长的 ZnO 薄膜，尽管出现了与缺陷相关的可见发射，但观察到 UV 发射峰向近直接带边（3.37 eV）复合发射偏移约 60 meV。高分辨率透射电子显微镜（HRTEM）表明，在 25°C 下获得的 ZnO 薄膜由 ZnO 纳米晶组成，平均半径为 2nm，嵌入在很大的非晶基质中。由于体相 ZnO 中自由激子的玻尔半径约为 2.3nm，可能发生了尺寸限制效应，导致了观察到的直接带边电子-空穴复合。此外，结果还表明，与在相同条件下直接沉积在 Si 衬底上的 ZnO 相比，ZnO/Si-NP 结构的发射效率提高了一个数量级。
