CVD两步法生长ZnO薄膜及其光致发光特性

用CVD两步法在常压下于p型Si(100)衬底上沉积出具有较好择优取向的多晶ZnO薄膜。在325nm波长的光激发下,室温下可观察到显著的紫外光发射(峰值波长381nm)。高温退火后氧空位缺陷浓度增加,出现了一个450~600nm的绿光发光带,发光峰值在510nm。作为比较,用一步法生长的ZnO薄膜结晶质量稍差。在其PL谱中不仅有峰值波长389nm的紫外发射而且还出现了一个很强的蓝光发光中心(峰值波长437nm),退火后同样产生绿光发光带。对这两种绿光发光带的发光机制进行了研究,认为前者源于VO,而后者与O_Zn有密切的关系。

Photoluminescence Properties for ZnO Films Grown by Two-step CVD

ZnO thin films with strong (002) preferred orientation have been deposited on Si(100) substrates using two-step AP-CVD. In the two-step growth process, a ZnO buffer layer was firstly grown at 450℃ for 5 min, and then a top layer was grown at 350℃ for 20 min. Arelatively high temperature buffer layer of ZnO provided a stable crystalline template for subsequent low temperature top layer to grow upon. In lattice-mismatched growth, ZnO thin film has a tensile built-in strain. The tensile strain in ZnO can be relaxed by providing sufficient thermal energy and meanwhile this relaxation process can give rise to more defects. Strong UV emission located at 381 nm is observed when excited with 325 nm light. The concentration of oxygen vacancies in the thin films increased after annealing at 800℃, and the 450~600 nm green emission band is observed. PLspectra for ZnO thin films grown by one-step method show typical UV emission located at 389 nm as well as blue emission centered at 437 nm. Likewise, the band of green emission is observed in PLspectra of thin films annealed at 800℃. The intensity of UV emission was dramatically decreased after annealing, which could be due to the increase of the size of ZnO particles and defect concentration. For the ZnO thin film grown by two-step method, the intensity of green luminescence after annealing in oxygen became weaker than that after annealing in air, so the corresponding mechanism for green emission is attributed to VO. For the ZnO thin film grown by one-step method, the intensity of green luminescence after annealed at oxygen became stronger than that after annealing in air. The relaxation process of tensile strain preferred to give rise to more O_Zn defects. Therefore, the corresponding mechanism for green emission is attributed to O_Zn. I-V properties also indicated that the emission mechanism of O_Zn was reasonable.