摘要
利用等离子体辅助分子束外延(P MBE)方法在(400)Si衬底上生长ZnO薄膜。为改善生长后样品的质量,把样品解理成三块后,在不同温度下氧气气氛中退火。通过X射线衍射(XRD)谱和光致发光(PL)谱进行表征,讨论了用P MBE方法在Si基上生长的ZnO的室温光致发光发光峰的可能原因。
Zinc oxide (ZnO) is an ⅡⅥ semiconductor with a wide direct band gap of 337eV at room temperature (RT) and a high exciton binding energy of 60meV. Because of this feature, ZnO is a promising candidate for use in ultraviolet wavelengths lightemitting devices and lasers.ZnO thin films have been grown on a (400) Si substrate by plasma molecular beam epitaxy (PMBE). Before growth, the Si substrate was chemically cleaned by a standard RCA process and then was thermally treated at 650℃ in ultrahigh vacuum for about 5min. During growth, the Si substrate temperature was at 450℃.The plasma power was kept up 300W. The zinc flux of purity zinc(6N) source and oxygen(5N) overpressure in the growth chamber were kept at around 4×10-5Pa and 6×10-3Pa, respectively. Obtained thickness of the sample is about 100nm(Sample S1).To improve the crystal quality, the samples were annealed in oxygen for two hours at temperature of 700℃(Sample S2), 800℃(Sample S3), and 900℃(Sample S4), respectively. The ZnO thin films were characterized by Xray using a rotating anode XRD with CuKα radiation wavelength of 0154nm. PL spectra were excited by 325nm line of a HeCd laser.The Xray diffraction spectra show a strong (002) diffraction peak and weaker other orientation peaks of the ZnO thin films. This indicates that the grown samples are polycrystalline structure. The full width at half maximum(FWHM) of S1, S2, S3 and S4 samples are 0257, 0244, 0236, 0206°, respectively. Above result proves that the crystal quality is improved with increasing annealing temperature.In the PL spectra, an ultraviolet (UV) emission is observed at RT for all samples. In order to verify the origin of this UV emission, temperature dependences of the PL intensities are measured. This UV band at RT comes from the emission of free exciton and radiative recombination of bound exciton associated with one LO phonon, in which bound exciton is considered to be related to deep centers.
出处
《发光学报》
EI
CAS
CSCD
北大核心
2003年第3期275-278,共4页
Chinese Journal of Luminescence
基金
国家"863"高技术新材料领域项目(209AA31112)
中国科学院二期创新项目
中国科学院百人计划项目
国家自然科学基金(69896260
69977019)资助项目
