氧对纳米ZnO薄膜晶体结构和光致发光的影响

THE EFFECT OF OXYGEN ON THE STRUCTURE OF CRYSTALLIZATION AND PHOTOLUMINESCENCE OF ZnO THIN FILM

ZnO是一种直接带半导体材料,在光电领域中和GaN一样受到关注.ZnO不仅有与GaN相似的晶体结构,而且它的激子结合能高达60meV,是GaN的2.4倍.采用射频(RF)磁控溅射法在n-Si(001)衬底上生长ZnO薄膜,XRD谱测量显示出氧压对ZnO薄膜的晶体结构有显著影响.用波长为325nm的激光激发,观察到在445nm处有一强的光致发光峰,它来自于氧空位浅施主能级上的电子跃迁到价带,分析了发光峰与氧压的关系以及退火对它的影响.

ZnO,a wide direct_gap semiconductor, attracts as much attention as GaN in optoelectronics research field. ZnO not only has the same crystal structure as GaN, but also has strong excition binding energy of 60 meV which is 2.4 times to that of GaN. ZnO thin films with a strong C_axis orientation have been successfully deposited on (001) silon substrate by radio frequency (r.f.) magnetron sputtering. The marked effect of oxygen on the structure of crystallization of ZnO thin film is demonstrated through the measure of XRD spectrum. All samples show typical luminescence behavior with a narrow 445 nm emission peak when excited with 325 nm light. The intensity of PL peaks is found to be strongly dependent on the oxygen during films deposition. As the oxygen partial pressure increase, the PL intensity decreases quickly. The blue emission is also affected by annealing in different ambient. For the vacuum annealed sample, the intensity of PL increases markedly on the cintrary, for the samples annealed in oxygen the PL intensity decreases. The experiments prove that the luminescence emission peak located at 445 nm corresponds to the electron transition from the shallow level of oxygen vacancy to valence band.